• 70S ribosome a prokaryotic ribosome composed of 50S and 30S subunits
• 80S ribosome cytoplasmic eukaryotic ribosome composed of 60S and 40S subunits

A

• A-B exotoxin class of exotoxin that contains A subunits, which enter the cell and disrupt cellular activities, and B subunits, which bind to host cell receptors
• ABO blood group system set of glycoprotein antigens found on the surface of red blood cells; the presence or absence of specific carbohydrates determining blood type
• absorbance when a molecule captures energy from a photon and vibrates or stretches, using the energy
• acellular not made of cells
• acid-fast stain a stain that differentiates cells that have waxy mycolic acids in their gram-positive cell walls
• acidophile organism that grows optimally at a pH near 3.0
• acne a skin disease in which hair follicles or pores become clogged, leading to the formation of comedones and infected lesions
• acquired immunodeficiency syndrome (AIDS) disease caused by HIV, characterized by opportunistic infections and rare cancers
• active carrier an infected individual who can transmit the pathogen to others regardless of whether symptoms are currently present
• active immunity stimulation of one’s own adaptive immune responses
• acute disease disease of a relatively short duration that develops and progresses in a predictable pattern
• acute glomerulonephritis inflammation of the glomeruli of the kidney, probably resulting from deposition of immune complexes and an autoimmune response caused by self-antigen mimicry by a pathogen
• acute-phase proteins antimicrobial molecules produced by liver cells in response to pathogen-induced stimulation events
• acyclovir antiviral guanosine analog; inhibits DNA replication
• adaptive immunity third-line defense characterized by specificity and memory
• Addison disease autoimmune disease affecting adrenal gland function
• adenine purine nitrogenous base found in nucleotides
• adenosine diphosphate (ADP) nucleotide derivative and relative of ATP containing only one high-energy phosphate bond
• adenosine monophosphate (AMP) adenine molecule bonded to a ribose molecule and to a single phosphate group, having no high-energy phosphate bonds
• adenosine triphosphate (ATP) energy currency of the cell; a nucleotide derivative that safely stores chemical energy in its two high-energy phosphate bonds
• adhesins molecules on the surface of pathogens that promote colonization of host tissue
• adhesion the capability of microbes to attach to host cells
• aerobic respiration use of an oxygen molecule as the final electron acceptor of the electron transport system
• aerotolerant anaerobe organism that does not use oxygen but tolerates its presence
• aflatoxin chemical produced by the fungus Aspergillus flavus; both a toxin and the most potent known natural carcinogen
• agglutination binding of different pathogen cells by Fab regions of the same antibody to aggregate and enhance elimination from body
• agranulocytes leukocytes that lack granules in the cytoplasm
• algae (singular: alga) any of various unicellular and multicellular photosynthetic eukaryotic organisms; distinguished from plants by their lack of vascular tissues and organs
• alkaliphile organism that grows optimally at pH above 9.0
• alkylating agent type of strong disinfecting chemical that acts by replacing a hydrogen atom within a molecule with an alkyl group, thereby inactivating enzymes and nucleic acids
• allergen antigen capable of inducing type I hypersensitivity reaction
• allergy hypersensitivity response to an allergen
• alveoli cul-de-sacs or small air pockets within the lung that facilitate gas exchange
• amantadine antiviral drug that targets the influenza virus by preventing viral escape from endosomes upon host cell uptake, thus preventing viral RNA release and subsequent viral replication
• Ames test method that uses auxotrophic bacteria to detect mutations resulting from exposure to
• amino acid a molecule consisting of a hydrogen atom, a carboxyl group, and an amine group bonded to the same carbon. The group bonded to the carbon varies and is represented by an R in the structural formula
• aminoglycosides protein synthesis inhibitors that bind to the 30S subunit and interfere with the ribosome’s proofreading ability, leading to the generation of faulty proteins that insert into and disrupt the bacterial cytoplasmic membrane
• amoebiasis intestinal infection caused by Entamoeba histolytica
• amoebic dysentery severe form of intestinal infection caused by Entamoeba histolytica, characterized by severe diarrhea with blood and mucus
• amphipathic a molecule containing both polar and nonpolar parts
• amphitrichous having two flagella or tufts of multiple flagella, with one flagellum or tuft located at each end of the bacterial cell
• anabolism chemical reactions that convert simpler molecules into more complex ones
• anaerobe chamber closed compartment used to handle and grow obligate anaerobic cultures
• anaerobe jar container devoid of oxygen used to grow obligate anaerobes
• anaerobic respiration use of a non-oxygen inorganic molecule, like CO₂, nitrate, nitrite, oxidized iron, or sulfate, as the final electron acceptor at the end of the electron transport system
• analytical epidemiology study of disease outbreaks to establish associations between an agent and a disease state through observational studies comparing groups of individuals
• anaphylactic shock another term for anaphylaxis
• anaphylaxis systemic and potentially life-threatening type I hypersensitivity reaction
• anthrax a disease caused by Bacillus anthracis; the cutaneous form causes a skin lesion to develop; gastrointestinal and inhalation anthrax have high mortality rates
• antibiotic-associated diarrhea diarrhea that develops after antibiotic treatment as a result of disruption to the normal microbiota; C. difficile is a particularly serious example
• antibody Y-shaped glycoprotein molecule produced by B cells that binds to specific epitopes on an antigen
• antibody-dependent cell-mediated cytotoxicity (ADCC) mechanism by which large pathogens are marked for destruction by specific antibodies and then killed by secretion of cytotoxins by natural killer cells, macrophages, or eosinophils
• anticodon three-nucleotide sequence of a mature tRNA that interacts with an mRNA codon through complementary base pairing
• antigen (also, immunogen) a molecule that stimulates an adaptive immune response
• antigenic able to stimulate an adaptive immune response
• antigenic drift form of slight antigenic variation that occurs because of point mutations in the genes that encode surface proteins
• antigenic shift form of major antigenic variation that occurs because of gene reassortment
• antigenic variation changing of surface antigens (carbohydrates or proteins) such that they are no longer recognized by the host’s immune system
• antigen-presenting cells (APC) macrophages, dendritic cells, and B cells that process and present foreign pathogen antigens for the purpose of activating T cells and adaptive immune defenses
• antimetabolites compounds that are competitive inhibitors for bacterial metabolic enzymes
• antimicrobial drugs chemical compounds, including naturally produced drugs, semisynthetic derivatives, and synthetic compounds, that target specific microbial structures and enzymes, killing specific microbes or inhibiting their growth
• antimicrobial peptides (AMPs) class of nonspecific, cell-derived chemical mediators with broad-spectrum antimicrobial properties
• antisepsis protocol that removes potential pathogens from living tissue
• antiseptic antimicrobial chemical that can be used safely on living tissue
• antiserum serum obtained from an animal containing antibodies against a particular antigen that was artificially introduced to the animal
• apoptosis programmed and organized cell death without lysis of the cell
• arachnoid mater middle membrane surrounding the brain that produces cerebrospinal fluid
• archaea any of various unicellular prokaryotic microorganisms, typically having cell walls containing pseudopeptidoglycan
• Archaea domain of life separate from the domains Bacteria and Eukarya
• artery large, thick-walled vessel that carries blood from the heart to the body tissues
• artificial active immunity immunity acquired through exposure to pathogens and pathogen antigens through a method other than natural infection
• artificial passive immunity transfer of antibodies produced by a donor to another individual for the purpose of preventing or treating disease
• ascariasis soil-transmitted intestinal infection caused by the large nematode roundworm Ascaris lumbricoides
• asepsis sterile state resulting from proper use of microbial control protocols
• aseptic technique method or protocol designed to prevent microbial contamination of sterile objects, locations, or tissues
• aspergillosis fungal infection caused by the mold Aspergillus; immunocompromised patients are primarily at risk
• asymptomatic carrier an infected individual who exhibits no signs or symptoms of disease yet is capable of transmitting the pathogen to others
• asymptomatic not exhibiting any symptoms of disease
• ATP synthase integral membrane protein that harnesses the energy of the proton motive force by allowing hydrogen ions to diffuse down their electrochemical gradient, causing components of this protein to spin, making ATP from ADP and P_i
• attachment binding of phage or virus to host cell receptors
• autoclave specialized device for the moist-heat sterilization of materials through the application of pressure to steam, allowing the steam to reach temperatures above the boiling point of water
• autotroph organism that converts inorganic carbon dioxide into organic carbon

B

• β-lactamases bacterially produced enzymes that cleave the β-lactam ring of susceptible β-lactam antimicrobials, rendering them inactive and conferring resistance
• β-lactams group of antimicrobials that inhibit cell wall synthesis; includes the penicillins, cephalosporins, carbapenems, and monobactams; inhibits the transpeptidase cross-linking activity of penicillin-binding proteins
• β-oxidation process of fatty acid degradation that sequentially removes two-carbon acetyl groups, producing NADH and FADH₂, on entry into the Krebs cycle
• B-cell receptors (BCRs) membrane-bound IgD and IgM antibody that bind specific antigen epitopes with Fab antigen-binding region
• B lymphocyte antibody-producing cells of humoral immunity; B cell
• bacillary dysentery gastrointestinal illness caused by Shigella bacteria, also called shigellosis
• bacillus (bacilli) rod-shaped prokaryotic cell
• bacitracin group of structurally similar peptides that block the movement of peptidoglycan precursors across the cell membrane, inhibiting peptidoglycan synthesis
• bacteremia condition marked by the presence of bacteria in the blood
• bacteria (singular: bacterium) any of various unicellular prokaryotic microorganisms typically (but not always) having cell wells that contain peptidoglycan
• bacterial lawn layer of confluent bacterial growth on an agar plate
• bacterial meningitis bacterial infection that results in an inflammation of the meninges
• bacterial vaginosis a condition caused by an overgrowth of bacteria in the vagina that may or may not cause symptoms
• bactericidal irreversible inhibition of a microbe’s ability to divide
• bactericide chemical or physical treatment that kills bacteria
• bacteriology the study of bacteria
• bacteriophage virus that infects bacteria
• bacteriostatic having the ability to inhibit bacterial growth, generally by means of chemical or physical treatment; reversible inhibition of a microbe’s ability to divide
• barophile organism that grows under high atmospheric pressure
• base sequence identity of the specific nucleotides present in a nucleic acid strand and their order within the strand
• basophils leukocytes with granules containing histamine and other chemicals that facilitate allergic responses and inflammation when released
• binary fission predominant form of bacterial reproduction in which one cell divides into two daughter cells of equal size, which separate, each offspring receiving a complete copy of the parental genome
• binocular having two eyepieces
• binomial nomenclature a universal convention for the scientific naming of organisms using Latinized names for genus and species
• biofilm complex ecosystem of bacteria embedded in a matrix
• biogeochemical cycle recycling of inorganic matter between living organisms and their nonliving environment
• biological transmission movement of a pathogen between hosts facilitated by a biological vector in which the pathogen grows and reproduces
• biological vector an animal (typically an arthropod) that is infected with a pathogen and is capable of transmitting the pathogen from one host to another
• biomarker a protein expressed by a cell or tissue that is indicative of disease
• biomolecule a molecule that is part of living matter
• biosynthesis replication of viral genome and other protein components
• biotechnology the science of using living systems to benefit humankind
• blood-brain barrier tight cell junctions of the endothelia lining the blood vessels that serve the central nervous system, preventing passage of microbes from the bloodstream into the brain and cerebrospinal fluid
• botulism form of flaccid paraylsis caused by the ingestion of a neurotoxin produced by Clostridium botulinum
• bradykinin activated form of a proinflammatory molecule induced in the presence of invader microbes; opens gaps between cells in blood vessels, allowing fluid and cells to leak into surrounding tissue
• brightfield microscope a compound light microscope with two lenses; it produces a dark image on a bright background
• broad-spectrum antimicrobial drug that targets many different types of microbes
• bronchitis inflammation of the bronchi
• budding unequal reproductive division in which a smaller cell detaches from the parent cell
• budding yeasts yeasts that divide by budding off of daughter cells
• Burkitt lymphoma disease characterized by rapidly growing solid tumor; caused by Epstein-Barr virus (HHV-4)
• burst release of new virions by a lysed host cell infected by a virus

C

• candidiasis fungal infection caused by Candida spp., especially C. albicans; can affect various regions of the body, e.g., skin (cutaneous candidiasis), oral cavity (oral thrush), or vagina (yeast infection)
• capsid protein coat surrounding the genome of the virus
• capsomere individual protein subunits that make up the capsid
• capsule staining a negative staining technique that stains around a bacterial capsule while leaving the capsule clear
• capsule type of glycocalyx with organized layers of polysaccharides that aid in bacterial adherence to surfaces and in evading destruction by immune cells
• carbohydrate the most abundant type of biomolecule, consisting of carbon, hydrogen, and oxygen
• carbon skeleton chain of carbon atoms to which one or more functional groups are bound
• carbuncle abscess containing a large, deep, purulent skin lesion
• carcinogen agent that causes cancer
• case-control study a type of observational study in which a group of affected individuals are compared, usually retrospectively, to a similar group of unaffected individuals
• catabolism chemical reactions that break down complex molecules into simpler ones
• catalase enzyme that breaks down hydrogen peroxide to water and oxygen
• catalyst molecule that increases the rate of a chemical reaction but is not used or changed during the chemical reaction and, thus, is reusable
• causative agent the pathogen or substance responsible for causing a particular disease; etiologic agent
• celiac disease disease largely of the small intestine caused by an immune response to gluten that results in the production of autoantibodies and an inflammatory response
• cell envelope the combination of external cellular structures (e.g., plasma membrane, cell wall, outer membrane, glycocalyces) that collectively contain the cytoplasm and internal structures of a cell
• cell membrane lipid bilayer with embedded proteins and carbohydrates that defines the boundary of the cell (also called the cytoplasmic membrane or plasma membrane)
• cell morphology cell shape, structure, and arrangement, as viewed microscopically
• cell theory the theory that all organisms are composed of cells and that the cell is the fundamental unit of life
• cell wall a structure in the cell envelope of some cells that helps the cell maintain its shape and withstand changes in osmotic pressure
• cellular immunity adaptive immunity involving T cells and the destruction of pathogens and infected cells
• cellulose a structural polysaccharide composed of glucose monomers linked together in a linear chain by glycosidic bonds
• central dogma scientific principle explaining the flow of genetic information from DNA to RNA to protein
• central nervous system (CNS) portion of the nervous system made up of the brain and spinal cord
• central tolerance negative selection of self-reactive T cells in thymus
• centrosome a microtubule-organizing center for the mitotic spindle found in animal cells; it separates chromosomes during cell division and is composed of a pair of centrioles positioned at right angles to each other
• cephalosporins a group of cell wall synthesis inhibitors within the class of β-lactams
• cerebrospinal fluid (CSF) sterile liquid produced in the brain that fills the subarachnoid space of the brain and spinal column
• chemical mediators chemicals or enzymes produced by a variety of cells; provide nonspecific antimicrobial defense mechanisms
• chemically defined media media in which all components are chemically defined
• chemiosmosis flow of hydrogen ions across the membrane through ATP synthase
• chemokines chemotactic cytokines that recruit specific subsets of leukocytes to infections, damaged tissue, and sites of inflammation
• chemotaxis directional movement of a cell in response to a chemical attractant
• chemotroph organism that gets its energy from the transfer of electrons originating from chemical compounds
• chickenpox common childhood disease caused by the varicella-zoster virus and marked by the formation of pustular lesions on the trunk
• chitin polysaccharide that is an important component of fungal cell walls
• chlamydia a common STI caused by Chlamydia trachomatis
• chloramphenicol protein synthesis inhibitor with broad-spectrum activity that binds to the 50S subunit, inhibiting peptide bond formation
• cholera gastrointestinal illness caused by Vibrio cholera characterized by severe diarrhea
• chromatin combination of DNA with DNA binding proteins
• chromosome discrete DNA structure within a cell that controls cellular activities
• chronic disease any disease that progresses and persists over a long time
• chronic granulomatous disease primary immunodeficiency caused by an impaired ability of phagocytic cells to kill ingested bacteria in the phagolysosome
• cilia (singular: cilium) short filamentous structures found on some eukaryotic cells; each is composed of microtubules in a 9+2 array, and may be used for locomotion, feeding, and/or movement of extracellular particles that come in contact with the cell
• ciliated epithelial cells hair-like cells in the respiratory tract that beat, pushing mucus secretions and trapped debris away from the sensitive tissues of the lungs
• clone a genetically identical cell or individual
• Clostridium perfringens gastroenteritis relatively mild gastrointestinal illness caused by C. perfringens
• clusters of differentiation (CD) cell-surface glycoproteins that serve to identify and distinguish white blood cells
• coagulase enzyme that causes the activation of fibrinogen to form fibrin, promoting clotting of the blood
• coarse focusing knob a knob on a microscope that produces relatively large movements to adjust focus
• codon three-nucleotide sequence within mRNA that specifies a particular amino acid to be incorporated into the polypeptide being synthesized
• coenzyme organic molecule required for proper enzyme function that is not consumed and is reusable
• cofactor inorganic ion that helps stabilize enzyme conformation and function
• cohort method a method used in observational studies in which a group of individuals is followed over time and factors potentially important in the development of disease are evaluated
• colitis inflammation of the large intestine
• collagenase enzyme that digests collagen, the dominant protein in connective tissue
• colony-forming unit (CFU) a counting quantity represented by a colony formed on solid medium from a single cell or a few cells
• commensalism type of symbiosis in which one population benefits and the other is not affected
• commercial sterilization type of sterilization protocol used in food production; uses conditions that are less harsh (lower temperatures) to preserve food quality but still effectively destroy vegetative cells and endospores of common foodborne pathogens such as Clostridium botulinum
• common cold most common cause of rhinitis in humans; associated with a variety of adenoviruses, coronaviruses, and rhinoviruses
• communicable able to be transmitted directly or indirectly from one person to another
• competitive interactions interactions between populations in which one of them competes with another for resources
• complement activation cascading activation of the complement proteins in the blood, resulting in opsonization, inflammation, and lysis of pathogens
• complement system series of proteins that can become activated in the presence of invading microbes, resulting in opsonization, inflammation, and lysis of pathogens
• complementary base pairs base pairing due to hydrogen bonding that occurs between a specific purine and a specific pyrimidine; A bonds with T (in DNA), and C bonds with G
• complex media media that contain extracts of animals and plants that are not chemically defined
• complex virus virus shape that often includes intricate characteristics not seen in the other categories of capsid
• compound microscope a microscope that uses multiple lenses to focus light from the specimen
• condenser lens a lens on a microscope that focuses light from the light source onto the specimen
• conjugate vaccine a vaccine consisting of a polysaccharide antigen conjugated to a protein to enhance immune response to the polysaccharide; conjugate vaccines are important for young children who do not respond well to polysaccharide antigens
• conjugation mechanism of horizontal gene transfer in bacteria in which DNA is directly transferred from one bacterial cell to another by a conjugation pilus
• conjugation pilus (sex pilus) hollow tube composed of protein encoded by the conjugation plasmid that brings two bacterial cells into contact with each other for the process of conjugation
• conjunctiva the mucous membranes covering the eyeball and inner eyelid
• conjunctivitis inflammation of the conjunctiva, the mucous membrane covering the eye and inside of the eyelid
• contact see exposure
• contact transmission movement of a pathogen between hosts due to contact between the two; may be direct or indirect
• contagious easily spread from person to person
• contrast visible differences between parts of a microscopic specimen
• counterstain a secondary stain that adds contrasting color to cells from which the primary stain has been washed out by a decolorizing agent
• crenation shriveling of a cell
• Creutzfeldt-Jakob disease form of transmissible spongiform encephalopathy found in humans; typically a fatal disease
• critical item object that must be sterile because it will be used inside the body, often penetrating sterile tissues or the bloodstream
• cryptococcosis fungal pneumonia caused by the encapsulated yeast Cryptococcus neoformans commonly found in bird droppings
• culture density the number of cells per volume of broth
• culture medium combination of compounds in solution that supports growth
• cutaneous mycosis any fungal infection that affects the surface of the skin, hair, or nails
• cysticerci larval form of a tapeworm
• cystitis inflammation of the bladder
• cysts microbial cells surrounded by a protective outer covering; some microbial cysts are formed to help the microbe survive harsh conditions, whereas others are a normal part of the life cycle
• cytokine storm an excessive release of cytokines, typically triggered by a superantigen, that results in unregulated activation of T cells
• cytokines protein molecules that act as a chemical signals; produced by cells in response to a stimulation event
• cytokinesis division of the cytoplasm following mitosis that forms two daughter cells
• cytoplasm the gel-like material composed of water and dissolved or suspended chemicals contained within the plasma membrane of a cell
• cytoplasmic membrane see cell membrane
• cytosine pyrimidine nitrogenous base found in nucleotides
• cytoskeleton a network of filaments or tubules in the eukaryotic cell that provides shape and structural support for cells; aids movement of materials throughout the cell
• cytotoxic T cells effector cells of cellular immunity that target and eliminate cells infected with intracellular pathogens through induction of apoptosis
• cytotoxicity harmful effects to host cell

D

• death phase (decline phase) phase of the growth curve at which the number of dying cells exceeds the number of new cells formed
• decimal reduction time (DRT) or D-value amount of time it takes for a specific protocol to produce a one order of magnitude decrease in the number of organisms; that is, death of 90% of the population
• decolorizing agent a substance that removes a stain, usually from some parts of the specimen
• definitive host the preferred host organism for a parasite, in which the parasite reaches maturity and may reproduce sexually
• degerming protocol that significantly reduces microbial numbers by using mild chemicals (e.g., soap) and gentle scrubbing of a small area of skin or tissue to avoid the transmission of pathogenic microbes
• degranulation release of the contents of mast cell granules in response to the cross-linking of IgE molecules on the cell surface with allergen molecules
• dermis the second layer of human skin, found between the epidermis and the hypodermis
• descriptive epidemiology a method of studying a disease outbreak using case histories, contact interviews, medical information, and other sources of information
• desensitization injections of antigen that lead to production of antigen-specific IgG molecules, effectively outcompeting IgE molecules on the surface of sensitized mast cells for antigen
• desiccation method of microbial control involving the removal of water from cells through drying or dehydration
• desquamation peeling and shedding of outermost skin
• diapedesis process by which leukocytes pass through capillary walls to reach infected tissue; also called extravasation
• diaphragm a component of a microscope; typically consists of a disk under the stage with holes of various sizes; can be adjusted to allow more or less light from the light source to reach the specimen
• differential media media that contain additives that make it possible to distinguish bacterial colonies based on metabolic activities of the organisms
• differential staining staining that uses multiple dyes to differentiate between structures or organisms
• diffraction the changing of direction (bending or spreading) that occurs when a light wave interacts with an opening or barrier
• dioecious refers to sexually reproducing organisms in which individuals have either male or female reproductive organs (not both)
• direct agglutination assay assay that can be used to detect the agglutination of bacteria by the action of antibodies in patient serum
• direct contact transmission movement of a pathogen between hosts by physical contact or transfer in droplets at a distance less than one meter
• direct ELISA enzyme-linked immunoabsorbent assay in which the antibodies are bound in the well of a microtiter plate; antigens present in an applied serum will then bind to antibodies in the well.
• direct hemagglutination assay test that determines the titer of certain bacteria and viruses that causes clumping of red blood cells
• direct microscopic cell count counting of cells using a calibrated slide under a light microscope
• disease any condition in which the normal structure or function of the body is damaged or impaired
• disinfectant antimicrobial chemical applied to a fomite during disinfection that may be toxic to tissues
• disinfection protocol that removes potential pathogens from a fomite
• disk-diffusion method a technique for measuring of the effectiveness of one or more antimicrobial agents against a known bacterium; involves measuring the zone(s) of inhibition around the chemical agent(s) in a culture of the bacterium
• doubling time the time it takes for the population to double; also referred to as generation time
• droplet transmission direct contact transmission of a pathogen transferred in sneezed or coughed droplets of mucus that land on the new host within a radius of one meter
• drug resistance ability of a microbe to persist and grow in the presence of an antimicrobial drug
• dry-heat sterilization protocol that involves the direct application of high heat
• dura mater tough, outermost membrane that surrounds the brain
• dysentery intestinal inflammation that causes diarrhea with blood and mucus
• dysuria urination accompanied by burning, discomfort, or pain

E

• edema swelling due to accumulation of fluid and protein in tissue as a result of increased permeability of capillary walls during an inflammatory response; chronic edema can also result from blockage of lymphatic vessels, as in the case of elephantiasis
• effector cells activated cells of cellular immunity that are involved in the immediate immune response, primarily to defend the body against pathogens
• electron carrier cellular molecule that accepts high-energy electrons from reduced molecules like foods and later serves as an electron donor in subsequent redox reactions
• electron microscope a type of microscope that uses short-wavelength electron beams rather than light to increase magnification and resolution
• electron transport system (ETS) series of membrane-associated protein complexes and associated mobile accessory electron carriers important in the generation of the proton motive force required for ATP production by chemiosmosis; the last component involved in the cellular respiration of glucose
• Embden-Meyerhof-Parnas (EMP) pathway type of glycolysis found in animals and the most common in microbes
• emerging infectious disease a disease that is new to the human population or has increased in prevalence over the previous 20 years
• encephalitis inflammation of the tissues of the brain
• encystment the process of forming a cyst
• endemic disease an illness that is constantly present (often at low levels) in a population
• endocarditis inflammation of the endocardium, especially the heart valves
• endocytosis the uptake of molecules through plasma membrane invagination and vacuole/vesicle formation
• endospore a cellular structure formed by some bacteria in response to adverse conditions; preserves DNA of the cell in a dormant state until conditions are favorable again
• endospore staining a differential staining technique that uses two stains to make bacterial endospores appear distinct from the rest of the cell
• endothelia layer of epithelial cells lining blood vessels, lymphatics, the blood-brain barrier, and some other tissues
• endotoxin lipid A component of lipopolysaccharides in the outer membrane of gram-negative bacteria
• enriched media media that contain additional essential nutrients to support growth
• enrichment culture media providing growth conditions that favor the expansion of an organism present in low numbers
• enteric bacteria of the family Enterobacteriaceae, which live in the human intestinal tract
• enteritis inflammation of the lining of the intestine
• enterohemorrhagic E. coli (EHEC) E. coli bacteria that cause severe gastrointestinal illness with potential serious complications such as hemolytic uremic syndrome
• enteropathogenic E. coli (EPEC) E. coli bacteria that cause serious gastrointestinal illness
• enterotoxin toxin that affects the intestines
• Entner-Doudoroff (ED) pathway alternative glycolytic pathway used by some bacteria
• enveloped virus a virus formed with a nucleic-acid packed capsid surrounded by a lipid layer
• enzyme catalyst for biochemical reactions inside cells
• enzyme immunoassay (EIA) type of assay
• enzyme-linked immunosorbent assay (ELISA) an assay wherein either the primary antibody or an antigen is first attached to a solid surface such as the well of a microtiter plate and allowed to interact with the complementary serum antigen or antibody; an enzyme is coupled to a secondary antibody that will bind to either bound antigen or antibody; addition of a chromogenic substrate for the antibody allows detection of the secondary antibody
• eosinophils leukocytes with granules containing histamine and major basic protein; facilitate allergic responses and protection against parasitic protozoa and helminths
• epidemic disease an illness with a higher-than-expected incidence in a given period within a given population
• epidemiology the study of where and when infectious diseases occur in a population and how they are transmitted and maintained in nature
• epididymitis inflammation of the epididymis caused by a bacterial infection
• epiglottitis inflammation of the epiglottis
• epitope smaller exposed region on an antigen that is recognized by B-cell and T-cell receptors and antibodies
• erythema redness at the site of inflammation, usually due to dilation of blood vessels in the area to help bring in white blood cells
• erythrocyte red blood cell
• erythrogenic toxin exotoxin produced by some strains of Streptococcus pyogenes; activity of the toxin can produce the characteristic rash of scarlet fever
• erythromycin protein synthesis inhibitor of the macrolide class that is often used as an alternative to penicillin
• eukaryote an organism made up of one or more cells that contain a membrane-bound nucleus and organelles
• eukaryotic cell has a nucleus surrounded by a complex nuclear membrane that contains multiple, rod-shaped chromosomes
• exocytosis the release of the contents of transport vesicles to the cell’s exterior by fusion of the transport vesicle’s membrane with the plasma membrane
• exotoxin biologically active product that causes adverse changes in the host cells
• experimental epidemiology the use of laboratory and clinical studies to directly study disease in a population
• experimental study a type of scientific study that involves manipulation of the study subjects by the researcher through application of specific treatments hypothesized to affect the outcome while maintaining rigorously controlled conditions
• exposure contact between potential pathogen and host; also called contamination or contact
• extracellular matrix material composed of proteoglycans and fibrous proteins secreted by some eukaryotic cells that lack cell walls; helps multicellular structures withstand physical stresses and coordinates signaling from the external surface of the cell to the interior of the cell
• extracellular polymeric substances (EPS) hydrated gel secreted by bacteria in a biofilm containing polysaccharides, proteins, nucleic acids, and some lipids
• extravasation process by which leukocytes pass through capillary walls to reach infected tissue; also called diapedesis

F

• F pilus (F pili) specialized type of pilus that aids in DNA transfer between cells; conjugation pilus of E. coli
• facultative anaerobe organism that grows better in the presence of oxygen but can proliferate in its absence
• false negative negative result to a test for an infection or condition (e.g., presence of antigen, antibody, or nucleic acid) when the infection or condition is actually present
• false positive positive result to a test for an infection or condition (e.g., presence of antigen, antibody, or nucleic acid) when the infection or condition is actually absent
• fastidious organism organism that has extensive growth requirements
• Fc region region on the trunk of an antibody molecule involved in complement activation and opsonization
• fermentation process that uses an organic molecule as a final electron acceptor to regenerate NAD⁺ from NADH such that glycolysis can continue
• fever system-wide sign of inflammation that raises the body temperature and stimulates the immune response
• fimbriae filamentous appendages found by the hundreds on some bacterial cells; they aid adherence to host cells
• fine focusing knob a knob on a microscope that produces relatively small movements to adjust focus
• fixation the process by which cells are killed and attached to a slide
• flagella long, rigid, spiral structures used by prokaryotic cells for motility in aqueous environments; composed of a filament made of flagellin, a hook, and motor (basal body) that are attached to the cell envelope
• flagella staining a staining protocol that uses a mordant to coat the flagella with stain until they are thick enough to be seen
• flagellum (eukaryotic) (plural: flagella) long, whip-like, filamentous external structure found on some eukaryotic cells; composed of microtubules in a 9+2 arrangement; used for locomotion
• flukes any of the parasitic nonsegmented flatworms (trematodes) that have an oral sucker and sometimes a second ventral sucker; they attach to the inner walls of intestines, lungs, large blood vessels, or the liver in human hosts
• focal infection infection in which the pathogen causes infection in one location that then spreads to a secondary location
• folliculitis a skin infection characterized by localized inflammation of hair follicles, typically producing an itchy red rash
• fomite inanimate item that may harbor microbes and aid in disease transmission
• foodborne disease disease that is transmitted through contaminated food
• fungi (singular: fungus) any of various unicellular or multicellular eukaryotic organisms, typically having cell walls made out of chitin and lacking photosynthetic pigments, vascular tissues, and organs
• fungicide chemical or physical treatment that kills fungi
• fungistatic having the ability to inhibit fungal growth, generally by means of chemical or physical treatment
• furuncle a small, purulent skin lesion; sometimes called a boil

G

• gas gangrene rapidly spreading infection of necrotic tissues caused by the gram-positive anaerobe Clostridium perfringens and other Clostridium spp.
• gastritis inflammation of the lining of the stomach
• gastroenteritis inflammation of the lining of the stomach and intestine
• generation time see doubling time
• genes segments of DNA molecules that code for proteins or stable RNA molecules
• genetic code correspondence between mRNA nucleotide codons and the translated amino acids
• genital herpes an STI caused by the herpes simplex virus
• genital warts soft, pink, irregular growths that develop in the external genitalia or anus as a result of human papillomavirus infection
• germ theory of disease the theory that many diseases are the result of microbial infection
• germination process of an endospore returning to the vegetative state
• Ghon complex calcified lesion containing Mycobacterium tuberculosis; forms in the lungs of patients with tuberculosis
• giardiasis intestinal infection caused by Giardia lamblia
• glomerulonephritis a type of kidney infection involving the glomeruli of the nephrons
• glycocalyx cell envelope structure (either capsules or slime layer) outside the cell wall in some bacteria; allows bacteria to adhere to surfaces, aids in biofilm formation, and provides protection from predation
• glycogen highly branched storage polysaccharide in animal cells and bacteria
• glycolipid complex lipid that contains a carbohydrate moiety
• glycolysis first step in the breakdown of glucose, the most common example of which is the Embden-Meyerhoff-Parnas pathway, producing two pyruvates, two NADH molecules, and two (net yield) ATP per starting glucose molecule
• gonorrhea a common STI of the reproductive system caused by Neisseria gonorrhoeae
• Gram stain procedure a differential staining technique that distinguishes bacteria based upon their cell wall structure
• granuloma walled-off area of chronically inflamed tissue containing microbial pathogens, macrophages, and cellular materials unable to be eliminated
• granzymes proteases released from a natural killer cell that enter the cytoplasm of a target cell, inducing apoptosis
• growth curve a graph modeling the number of cells in a culture over time
• gummas granulomatous lesions that develop in tertiary syphilis

H

• halophile organism that depends on high concentrations of salt in the environment to grow
• halotolerant organism that grows in the presence of high salt concentration but does not require it
• hapten a molecule that is too small to be antigenic alone but becomes antigenic when conjugated to a larger protein molecule
• hard chancre a generally painless ulcer that develops at the site of infection in primary syphilis
• healthcare-associated infection (HAI) an infection acquired in a hospital or other health-care facility unrelated to the reason for which the patient was initially admitted; nosocomial infection
• helical virus cylindrical or rod shaped
• helminth a multicellular parasitic worm
• helper T cells class of T cells that is the central orchestrator of the cellular and humoral defenses of adaptive immunity and the cellular defenses of innate immunity
• hemagglutination visible clumping of red blood cells that can be caused by some viruses, bacteria, and certain diseases in which antibodies are produced that bind to self-red blood cells
• hematopoiesis formation, development, and differentiation of blood cells from pluripotent hematopoietic stem cells
• hematuria condition in which there is blood in the urine
• hemolysin class of exotoxin that targets and lyses red blood cells, as well as other cells
• hemorrhagic fever with renal syndrome serious hemorrhagic fever caused by hantavirus infection
• HEPA filter high-efficiency particulate air filter with an effective pore size that captures bacterial cells, endospores, and viruses as air passes through, removing them from the air
• hepatitis inflammation of the liver
• herd immunity a reduction in disease prevalence brought about when few individuals in a population are susceptible to an infectious agent
• herpes simplex virus type 2 (HSV-2) the type of herpesvirus most commonly associated with genital herpes
• heterotroph organism that uses fixed organic carbon compounds as its carbon source
• hexose monophosphate shunt see pentose phosphate pathway
• histamine proinflammatory molecule released by basophils and mast cells in response to stimulation by other cytokines and chemical mediators
• histones DNA-binding proteins found in eukaryotes and archaea that aid in orderly packaging of chromosomal DNA
• horizontal direct transmission movement of a pathogen from one host to another (excluding mother to embryo, fetus, or infant) in a population through physical contact or through droplet transmission
• horizontal gene transfer introduction of genetic material from one organism to another organism within the same generation
• host range the types of host cells that a particular virus is able to infect
• HTST high-temperature short-time pasteurization is a method of pasteurization commonly used for milk in which the milk is exposed to a temperature of 72 °C for 15 seconds
• human immunodeficiency virus (HIV) retrovirus responsible for acquired immune deficiency syndrome (AIDS) in humans
• human papillomavirus (HPV) a group of common sexually transmitted viruses that may be associated with genital warts or with cervical cancer
• humoral immunity adaptive immunity mediated by antibodies produced by B cells
• hyaluronidase enzyme produced by pathogens that degrades hyaluronic acid between adjacent cells in connective tissue
• hyperthermophile a microorganism that has an optimum growth temperature close to the temperature of boiling water
• hypertonic medium an environment in which the solute concentration outside a cell exceeds that inside the cell, causing water molecules to move out of the cell, resulting in crenation (shriveling) or plasmolysis.
• hyphae tubular, filamentous structures that makes up most fungi
• hypotonic medium an environment in which the solute concentration inside a cell exceeds that outside the cell, causing water molecules to move into the cell, possibly leading to swelling and possibly lysis

I

• icosahedral three-dimensional, 20-sided structure with 12 vertices
• IgA antibody dimer primarily found in breast milk, mucus, saliva, and tears
• IgD membrane-body antibody monomer functioning as receptor on the surface of B cells
• IgE antibody monomer involved in defense against parasites and allergic reactions
• IgG antibody monomer most abundant in serum; able to cross placenta; most versatile class of antibody in terms of function
• IgM antibody that is a monomer when functioning as a receptor on surface of B cells but a pentamer when secreted in response to specific pathogens; first antibody to respond during primary and secondary responses
• imidazoles class of antifungal drugs that inhibit ergosterol biosynthesis
• immune complex large group of antigens bound by antibodies; large enough to settle out of fluid suspension
• immunoglobulin antibody
• impetigo a skin infection that may result in vesicles, blisters, or bullae especially around the mouth, commonly caused by Staphylococcus aureus, S. pyogenes, or a combination of both S. aureus and S. pyogenes
• in vitro outside the organism in a test tube or artificial environment
• in vivo inside the organism
• inactivated vaccine vaccine composed of whole pathogen cells or viruses that have been killed or inactivated through treatment with heat, radiation, or chemicals
• incidence the number of individuals with new infections of a particular disease in a given period of time
• inclusions prokaryotic cell cytoplasmic structures for storing specific nutrients and other resources needed by cells
• incubation period the first stage of acute disease, during which the pathogen begins multiplying in the host and signs and symptoms are not observable
• indirect agglutination assay assay that can be used to detect the agglutination of small latex beads; beads may be coated with antigen when looking for the presence of specific antibodies, or with antibody when looking for the presence of antigen
• indirect contact transmission transfer of an infectious agent between hosts through contact with a fomite
• indirect ELISA an assay in which an antigen from a pathogen is first attached to the wells of a microtiter plate; the antigen then captures antibodies from patient serum to determine whether the patient currently has or previosly had the disease
• infection the successful colonization of a microorganism within a host
• infectious disease disease caused by a pathogen
• infectious mononucleosis common and mild infection caused by Epstein-Barr virus (HHV-4) or cytomegalovirus (HHV-5); transmitted by direct contact with body fluids such as saliva
• inflammation innate nonspecific immune response characterized by erythema, edema, heat, pain, and altered function, typically at the site of injury or infection but sometimes becoming systemic.
• influenza highly contagious and acute viral disease of the respiratory tract caused by the influenza virus
• inoculum small number of cells added to medium to start a culture
• inorganic phosphate (P_i) single phosphate group in solution
• interferons cytokines released by cells that have been infected with a virus; stimulate antiviral responses in nearby cells
• interleukins cytokines largely produced by immune system cells that help coordinate efforts against invading pathogens
• intermediate host a host in which a parasite goes through some stages of its life cycle before migrating to the definitive host
• intrinsic growth rate genetically determined generation time under specific conditions for a bacterial strain
• invasion dissemination of a pathogen through local tissues or throughout the body
• iodophor compound in which iodine is complexed to an organic molecule, increasing the stability and efficacy of iodine as a disinfectant
• ionizing radiation high-energy form of radiation that is able to penetrate surfaces and sterilize materials by damaging microbial cell components and DNA
• ischemia condition marked by the inadequate flow of blood to the tissues
• isotonic medium a solution in which the solute concentrations inside and outside the cell are approximately equal, thereby creating no net movement of water molecules across the cell membrane
• ivermectin antihelminthic drug of the avermectin class that binds to invertebrate glutamate-gated chloride channels to block neuronal transmission in helminths

J

• jaundice yellowish color of the skin and mucous membranes caused by excessive bilirubin caused by a failure of the liver to effectively process the breakdown of hemoglobin

K

• Kirby-Bauer disk diffusion test simple, rapid method for determining susceptibility and resistance of a bacterial pathogen to antibacterial drugs. The test involves drug-impregnated disks placed on an agar plate inoculated with a bacterial lawn.
• Koplik’s spots white spots that form on the inner lining of the cheek of patients with measles
• Krebs cycle cyclic pathway during which each two-carbon unit entering the cycle is further oxidized, producing three NADH, one FADH₂, and one ATP by substrate-level phosphorylation, releasing two CO₂ molecules and regenerating the molecule used in the first step; also called the citric acid cycle or the tricarboxylic acid cycle
• kuru rare form of transmissible spongiform encephalopathy endemic to Papua New Guinea

L

• lag period the time between antigen exposure and production of antibodies
• lag phase interval before exponential growth of a microbial population during which cells adjust to a new environment
• laryngitis inflammation of the larynx
• latent disease disease that goes into a dormant nonreplicative state after the acute disease and can persist in this state for years, with the risk of reactivation back into acute disease
• latent virus virus that remains dormant in the host genome
• leukocidin class of exotoxin that targets and lyses leukocytes
• leukocytes white blood cells of various types, including granulocytes, lymphocytes, and monocytes
• leukotrienes lipid-based chemical mediators produced by leukocytes and other tissue cells; promote inflammation and allergic responses
• lipase extracellular enzyme that degrades triglycerides
• lipopolysaccharide (LPS) lipid molecules with attached sugars that are found as components of gram-negative outer membranes
• lipoprotein conjugated protein attached to a lipid
• listeriosis bacterial disease caused from the ingestion of the microbe Listeria monocytogenes
• lithotroph chemotroph that uses inorganic chemicals as its electron source; also known as chemoautotroph
• live attenuated vaccine vaccine with live pathogen that has been attenuated to become less virulent in order to produce an active but subclinical infection
• local infection infection in one limited area
• log phase interval of growth when cells divide exponentially; also known as the exponential growth phase
• lophotrichous having a single tuft of flagella located at one end of a bacterial cell
• lymph nodes bean-shaped organs situated throughout the body that contain areas called germinal centers, which are rich in B and T lymphocytes; also contain macrophages and dendritic cells for antigen presentation
• lymphadenitis inflammation of the lymph nodes
• lymphangitis inflammation of the lymphatic vessels
• lyophilization rapid freezing, followed by placement under a vacuum, of a material so that water is lost by sublimation, thereby inhibiting microbial growth
• lysis destruction of the host cell
• lysosome an organelle of the endomembrane system that contains digestive enzymes that break down engulfed material such as foodstuffs, infectious particles, or damaged cellular components

M

• M protein a streptococcal cell wall protein that protects the bacteria from being phagocytized. It is associated with virulence and stimulates a strong immune response
• macromolecule polymer assembled from of individual units, monomers, that bind together like building blocks
• macronutrient element required in abundance in cells; account for approximately 99% of the cell’s dry weight
• macrophages monocytes that have left the bloodstream and differentiated into tissue-specific phagocytes
• mad cow disease form of transmissible spongiform encephalopathy primarily affecting cattle; can be transmitted to humans by consumption of contaminated cattle products
• magnetosomes inclusions in certain bacterial cells containing magnetic iron oxide or iron sulfide, which allows bacteria to align along a magnetic field by magnetotaxis
• magnification the power of a microscope (or lens) to produce an image that appears larger than the actual specimen, expressed as a factor of the actual size
• major histocompatibility complex (MHC) collection of genes that code for MHC glycoproteins expressed on the surface of all nucleated cells
• malaise a general feeling of being unwell
• malaria potentially fatal, mosquito-borne protozoan infection caused by several species of Plasmodium and characterized by a relapsing fever, nausea, vomiting, and fatigue
• mast cells granulocytes similar in origin and function to basophils, but residing in tissues
• maturation assembly of viral components to produce a functional virus
• mature naïve T cell a T cell that has exited the thymus after thymic selection but has not yet been activated
• maximum growth pH highest pH value that an organism can tolerate for growth
• maximum growth temperature highest temperature at which a microorganism will divide or survive
• maximum permissible oxygen concentration highest concentration of oxygen at which an organism will grow
• measles highly contagious respiratory disease caused by the measles virus (MeV); marked by an intense macular rash and high fever; also known as rubeola
• mechanical transmission transfer of a pathogen between hosts by a mechanical vector
• mechanical vector an animal that transfers a pathogen from one host to another or from a reservoir to a host without being infected by the pathogen itself
• median infectious dose (ID₅₀) concentration of pathogen that will produce active infection in 50% of test animals inoculated
• median lethal dose (LD₅₀) concentration of pathogen that kills 50% of infected test animals
• meiosis a two-stage nuclear division process that results in four genetically distinct gametes
• membrane attack complex (MAC) ring structure formed from complement proteins C6 through C9 that penetrates the membranes of a targeted cell, causing cell lysis and death
• membrane filtration method to remove bacteria from liquid, typically heat-sensitive solutions, using filters with an effective pore size of 0.2 µm or smaller, depending on need
• membrane-bound ribosome 80S eukaryotic ribosome attached to rough endoplasmic reticulum
• membrane-disrupting toxin toxin that affects cell membrane function by either forming pores or disrupting the phospholipid bilayer
• memory B cell an activated and differentiated B cell that is programmed to respond to secondary exposures to a specific antigen
• memory helper T cell a long-lived T cell programmed to recognize and quickly mount a secondary response to a specific pathogen upon re-exposure
• memory the ability of the specific adaptive immune system to quickly respond to pathogens to which it has previously been exposed
• meninges membranes that surround the brain
• meningitis inflammation of the meningeal membranes that surround the brain
• meningococcal meningitis bacterial infection caused by Neisseria meningitidis that results in an inflammation of the meninges
• meningoencephalitis inflammatory response that involves both the brain and the membranes that surround it
• mesophile a microorganism that grows best at moderate temperatures, typically between about 20 °C and 45 °C
• metabolism all of the chemical reactions inside of cells
• methanogen microorganism that produces gaseous methane
• methicillin-resistant Staphylococcus aureus (MRSA) pathogen resistant to all β-lactams through acquisition of a new low-affinity penicillin-binding protein, and often resistant to many other drug classes
• MHC I molecule glycoprotein expressed on the surface of all nucleated cells and involved in the presentation of normal “self” antigens and foreign antigens from intracellular pathogens
• MHC II molecule glycoprotein expressed only on the surface of antigen-presenting cells and involved in the presentation of foreign antigens from pathogens ingested by phagocytosis
• micelle simple spherical arrangement of amphipathic lipid molecules with nonpolar tails aggregated within the interior and polar heads forming the outer surface
• microaerophile organism that requires oxygen at levels lower than atmospheric concentration
• microbe generally, an organism that is too small to be seen without a microscope; also known as a microorganism
• microbial death curve graphical representation of the progress of a particular microbial control protocol
• microbial ecology study of the interactions between microbial populations
• microbiology the study of microorganisms
• microbiome all prokaryotic and eukaryotic microorganisms and their genetic material that are associated with a certain organism
• microfilament cytoskeletal fiber composed of actin filaments
• micronutrient indispensable element present in cells in lower amounts than macronutrients; also called trace element
• microorganism generally, an organism that is too small to be seen without a microscope; also known as a microbe
• microtiter plates plastic dishes with multiple small wells
• microtubule hollow tube composed of tubulin dimers (α and β tubulin); the structural component of the cytoskeleton, centrioles, flagella, and cilia
• miliary tuberculosis hematogenous dissemination and spread of Mycobacterium tuberculosis from tubercles
• minimum growth pH lowest pH value that an organism can tolerate for growth
• minimum growth temperature lowest temperature at which a microorganism will divide or survive
• minimum permissible oxygen concentration lowest concentration of oxygen at which an organism will grow
• mitochondrial matrix the innermost space of the mitochondrion enclosed by two membranes; the location of many metabolic enzymes as well as the mitochondrial DNA and 70S ribosomes
• mitochondrion (plural: mitochondria) large, complex organelle that is the site of cellular respiration in eukaryotic cells
• mitosis(also, karyokinesis) period of the cell cycle during which the duplicated chromosomes are separated into identical nuclei; includes prophase, prometaphase, metaphase, anaphase, and telophase
• mitotic phaseperiod of the cell cycle during which duplicated chromosomes are distributed into two nuclei and cytoplasmic contents are divided; includes karyokinesis (mitosis) and cytokinesis
• moist-heat sterilization protocol that involves steam under pressure in an autoclave, allowing the steam to reach temperatures higher than the boiling point of water
• mold a multicellular fungus, typically made up of long filaments
• monocytes large, agranular, mononuclear leukocytes found in the peripheral blood; responsible for phagocytosis of pathogens and damaged cells
• monoecious refers to sexually reproducing organisms in which individuals have both male and female reproductive organs
• monomer small organic molecule that binds with like molecules, forming a polymer or macromolecule
• monosaccharide monomer for the synthesis of carbohydrate polymers; the simplest carbohydrate, called a simple sugar
• monotrichous having one flagellum, typically located on one end of the bacterial cell
• morbidity a state of illness
• morbidity rate the number of cases of a disease expressed as a percentage of the population or number per standard part of the population, such as 100,000
• mordant a chemical added to a specimen that sets a stain
• mortality death
• mortality rate the number of deaths from a disease expressed as a percentage of the population or number per standard part of the population, such as 100,000
• mRNA short-lived type of RNA that serves as the intermediary between DNA and the synthesis of protein products
• mucociliary escalator system by which mucus and debris are propelled up and out of the respiratory tract by the beating of respiratory cilia and the mechanical actions of coughing or swallowing
• mucous membrane moist layer of epithelial cells and interspersed goblet cells that lines the inner surfaces of the body, usually bathed in antimicrobial secretions from the cells of the membrane
• mucus viscous secretion produced by cells and glands in various mucous membranes throughout the body; helps trap and remove microbes and debris from the body
• multidrug-resistant microbes (MDR) group of pathogens that carry one or more resistance mechanisms, making them resistant to multiple antimicrobials; also called superbugs
• mutation heritable change in the DNA sequence of an organism
• mutualism type of symbiosis in which two populations benefit from, and depend on, each other
• mycelium vegetative network of branched, tubular hyphae
• mycolic acids waxy molecules associated with peptidoglycan in some gram-positive, acid-fast bacteria, chiefly mycobacteria
• mycology the study of fungi
• Mycoplasma pneumonia also known as walking pneumonia; a milder form of atypical pneumonia caused by Mycoplasma pneumoniae
• mycoses (mycosis, sing.) refers to diseases caused by fungi
• mycotoxin biologically active product of pathogenic fungi that causes adverse changes in the host cells
• myocarditis inflammation of the heart muscle tissues

N

• naïve mature B cell a B cell that has not yet been activated
• naked virus virus composed of a nucleic acid core, either DNA or RNA, surrounded by a capsid
• narrow-spectrum antimicrobial drug that targets only a specific subset of microbes
• natural active immunity immunity that develops as a result of natural infection with a pathogen
• natural antibiotic antimicrobial compound that is produced naturally by microorganisms in nature
• natural killer cells (NK cells) lymphoid cells that recognize and destroy abnormal target cells by inducing apoptosis
• natural passive immunity transfer of maternal antibodies from mother to fetus (transplacentally) or infant (via breastmilk)
• necrotizing fasciitis a serious infection, also known as flesh-eating disease, that leads to rapid destruction of tissue through the action of exotoxin A; it can be caused by S. pyogenes or several other bacterial species
• negative (–) single-strand RNA (–ssRNA) a viral RNA strand that cannot be translated until it is replicated into positive single-strand RNA by viral RNA-dependent RNA polymerase
• Nematoda phylum comprising roundworms
• neonatal herpes herpes infection of the newborn, generally caused by infection during birth
• neonatal meningitis meningitis caused by Group B streptococcus and occurring primarily in neonates (less than 2 months old)
• neonatal tetanus tetanus acquired through infection of the cut umbilical cord
• neutralization binding of an antibody to a pathogen or toxin, preventing attachment to target cells
• neutrophile organism that grows best at a near a neutral pH of 6.5–7.5
• neutrophils leukocytes with a multilobed nucleus found in large numbers in peripheral blood; able to leave the bloodstream to phagocytose pathogens in infected tissues; also called polymorphonuclear neutrophils (PMNs)
• nicotine adenine dinucleotide (NAD⁺/NADH) oxidized/reduced forms of an electron carrier in cells
• nicotine adenine dinucleotide phosphate (NADP⁺/NADPH) oxidized/reduced forms of an electron carrier in cells
• nitrogenous base nitrogen-containing ring structure within a nucleotide that is responsible for complementary base pairing between nucleic acid strands
• noncoding DNA regions of an organism’s genome that, unlike genes, do not encode proteins
• noncommunicable disease disease that is not transmitted from one person to another
• noncritical item object that may contact intact skin but does not penetrate it; requires cleanliness but not a high level of disinfection
• nonenveloped virus naked virus
• noninfectious disease disease caused by something other than an infectious agent (e.g., genetics, environment, nutritional deficiencies)
• nonionizing radiation low-energy radiation, like ultraviolet light, that can induce dimer formation between two adjacent pyrimidine bases, resulting in DNA polymerase stalling and possible formation of a frameshift mutation
• nosocomial disease disease acquired in a hospital setting
• nucleic acid class of macromolecules composed of nucleotide monomers polymerized into strands
• nucleoid concentrated area of DNA genome and associated proteins found in a prokaryotic cell that is not surrounded by a membrane
• nucleotide nucleic acid monomer composed of a pentose sugar, a phosphate group, and a nitrogenous base
• nucleus a membrane-bound structure of eukaryotic cells that houses the DNA genome

O

• objective lenses on a light microscope, the lenses closest to the specimen, typically located at the ends of turrets
• obligate aerobe organism that requires oxygen for growth
• obligate anaerobe organism that dies in the presence of oxygen
• obligate intracellular pathogen microorganism that cannot synthesize its own ATP and, therefore, must rely on a host cell for energy; behaves like a parasite when inside a host cell, but is metabolically inactive outside of a host cell
• observational study a type of scientific study that involves measurement of study subjects on variables hypothesized to be associated with the outcome of interest, but without any manipulation of the subjects
• ocular lens on a microscope, the lens closest to the eye (also called an eyepiece)
• oil immersion lens a special objective lens on a microscope designed to be used with immersion oil to improve resolution
• opacity the property of absorbing or blocking light
• opportunistic pathogen microorganism that can cause disease in individuals with compromised host defenses
• opsonin any molecule that binds to and coats the outside of a pathogen, identifying it for destruction by phagocytes (examples include antibodies and the complement proteins C3b and C4b)
• opsonization process of coating a pathogen with a chemical substance (an opsonin) that allows phagocytic cells to recognize, engulf, and destroy the pathogen more easily
• optimum growth pH the pH at which an organism grows best
• optimum growth temperature the temperature at which a microorganism’s growth rate is highest
• optimum oxygen concentration the ideal concentration of oxygen for a particular microorganism
• oral herpes an infection caused by herpes simplex virus that results in cold sores, most commonly on and around the lips
• oral thrush Candida infection of the mouth
• orchitis inflammation of one or both of the testes
• organic molecule composed primarily of carbon; typically contains at least one carbon atom bound to one or more hydrogen atoms
• organotroph chemotroph that uses organic molecules as its electron source; also known as chemoheterotroph
• osmosis diffusion of water across a semipermeable membrane
• osmotic pressure the force or pressure generated by water diffusing across a semipermeable membrane, driven by differences in solute concentration across the membrane
• outer membrane a phospholipid bilayer external to the peptidoglycan layer found in gram-negative cell walls
• oxidation reaction chemical reaction that removes electrons (often as part of H atoms) from donor molecules, leaving them oxidized
• oxidative phosphorylation mechanism for making ATP that uses the potential energy stored within an electrochemical gradient to add P_i to ADP

P

• pandemic disease an epidemic that is worldwide as opposed to regional
• papilloma growth on the skin associated with infection by any of the human papilloma viruses (HPV); commonly known as a wart
• parasitism type of symbiosis in which one population benefits while harming the other parasitology the study of parasites
• parenteral route means of entry by a pathogen through skin or mucous membranes when these barriers are breached
• paroxysmal stage most serious stage of pertussis (whooping cough), characterized by severe and prolonged coughing spells
• passive carrier an individual capable of transmitting a pathogen to another individual without becoming infected
• passive immunity adaptive immune defenses received from another individual or animal
• pasteurization form of microbial control using heat that is applied to foods; kills pathogens and reduces the number of spoilage-causing microbes while maintaining food quality
• pathogen a disease-causing microorganism
• pathogen-associated molecular patterns (PAMPs) common molecular motifs found on pathogens
• pathogenicity ability of a microbial agent to cause disease
• pattern recognition receptors (PRRs) receptors on the surface or in the interior of phagocytic cells that bind to pathogen-associated molecular patterns (PAMPs)
• pelvic inflammatory disease (PID) infection of the female reproductive organs that may spread from the vagina to the cervix, uterus, fallopian tubes, and ovaries
• penetration entry of phage or virus into a host cell through injection, endocytosis, or membrane fusion
• penicillin β-lactam antibacterial that was the first cell wall synthesis inhibitor developed
• pentose phosphate pathway (PPP) alternative glycolytic pathway that produces intermediates used for the biosynthesis of nucleotides and amino acids; also called the phosphogluconate pathway or the hexose monophosphate shunt
• peptic ulcer an ulcer in the lining of the stomach or duodenum, often associated with Helicobacter pylori
• peptidoglycan (murein) the polymer of alternating N-acetylmuramic acid NAM and N-acetylglucosamine (NAG) subunits linked together by peptide chains; a major constituent of bacterial cell walls
• perforin compound released from a natural killer cell that creates pores in the target cell through which other toxins (particularly granzymes) can gain access to the cytoplasm
• pericarditis inflammation of the sac that surrounds the heart
• period of convalescence fifth stage of acute disease, during which the patient returns to normal function
• period of decline fourth stage of disease, during which the number of pathogens present in the host decreases, along with signs and symptoms of disease
• period of illness third stage of acute disease, during which the number of pathogens present in the host is greatest and the signs and symptoms of disease are most severe
• peripheral tolerance mechanism by which regulatory T cells inhibit self-reactive immune responses in T cells that have already exited the thymus
• periplasmic space the space between the cell wall and the plasma membrane, primarily in gram-negative bacteria
• peristalsis muscular contractions of the gastrointestinal tract that propel ingested material through the stomach, intestines, and, eventually, through the rectum and out of the body
• peritrichous having numerous flagella covering the entire surface of a bacterial cell
• peroxidase enzyme that catalyzes the detoxification of peroxides
• peroxygen type of strong oxidizing agent that causes free radical formation in cells; can be used as a disinfectant or antiseptic
• pertussis contagious illness caused by Bordetella pertussis that causes severe coughing fits followed by a whooping sound during inhalation; commonly known as whooping cough
• pertussis toxin main virulence factor accounting for the symptoms of whooping cough
• petechiae small red or purple spots on the skin that result from blood leaking out of damaged vessels
• Peyer’s patches lymphoid tissue in the ileum that monitors and fights infections
• phagocytosis a type of endocytosis in which large particles are engulfed by membrane invagination, after which the particles are enclosed in a pocket, which is pinched off from the membrane to form a vacuole
• phagolysosome compartment in a phagocytic cell that results when the phagosome is fused with the lysosome, leading to the destruction of the pathogens inside
• phagosome compartment in the cytoplasm of a phagocytic cell that contains the phagocytosed pathogen enclosed by part of the cell membrane
• pharyngitis inflammation of the pharynx
• phenolics class of chemical disinfectants and antiseptics characterized by a phenol group that denatures proteins and disrupts membranes
• phenotype observable characteristics of a cell or organism
• phosphogluconate pathway see pentose phosphate pathway
• phospholipase enzyme that degrades phospholipids
• phospholipid complex lipid that contains a phosphate group
• phototaxis directional movement using flagella in response to light
• phototroph organism that gets its energy from light
• phylogeny the evolutionary history of a group of organisms
• pili long protein extensions on the surface of some bacterial cells; specialized F or sex pilus aids in DNA transfer between cells
• pinocytosis a type of endocytosis in which small dissolved materials are endocytosed into smaller vesicles
• planktonic free-floating or drifting in suspension
• plaque clear area on bacterial lawn caused by viral lysis of host cells
• plasma cell activated and differentiated B cell that produces and secretes antibodies
• plasma fluid portion of the blood that contains all clotting factors
• plasma membrane (also called the cell membrane or cytoplasmic membrane) lipid bilayer with embedded proteins that defines the boundary of the cell
• plasmid small, circular, double-stranded DNA molecule that is typically independent from the bacterial chromosome
• plasmolysis the separation of the plasma membrane away from the cell wall when a cell is exposed to a hypertonic environment
• platelets cell fragments in the peripheral blood that originate from megakaryocyte cells in the bone marrow; also called thrombocytes
• Platyhelminthes phylum comprising flatworms
• pleomorphic able to change shape
• pneumococcal meningitis bacterial infection caused by Streptococcus pneumoniae that results in an inflammation of the meninges
• Pneumocystis pneumonia common pulmonary infection in patients with AIDS; caused by P. jirovecii
• pneumonia pulmonary inflammation that causes the lungs to fill with fluids
• polyhedral virus virus with a three-dimensional shape with many facets
• polymorphonuclear neutrophil (PMN) see neutrophils
• polymyxins lipophilic polypeptide antibiotics that target the lipopolysaccharide component of gram-negative bacteria and ultimately disrupt the integrity of their outer and inner membranes
• portal of entry anatomical feature of the body through which pathogens can enter host tissue
• portal of exit anatomical feature of the body through which pathogens can leave diseased individual
• positive (+) strand viral RNA strand that acts like messenger RNA and can be directly translated inside the host cell
• pour plate method a technique used for inoculating plates with diluted bacterial samples for the purpose of cell counting; cells are mixed with warm liquid agar before being poured into Petri dishes
• prevalence the total number or proportion of individuals in a population ill with a specific disease
• primary antibody in a direct (sandwich) ELISA, the antibody that is attached to wells of a microtiter plate to capture antigen from a solution, or in an indirect ELISA, the antigen-specific antibody present in a patient’s serum
• primary immunodeficiency genetic condition that results in impaired immune function
• primary infection initial infection produced by a pathogen
• primary lymphoid tissue one of two types of lymphatic tissue; comprises bone marrow and the thymus
• primary pathogen microorganism that can cause disease in the host regardless of the effectiveness of the host’s immune system
• primary response the adaptive immune response produced upon first exposure to a specific antigen
• primary stain refers, in differential staining techniques, to the first dye added to the specimen
• prion acellular infectious particle consisting of just proteins that can cause progressive diseases in animals and humans
• prodromal period second stage of acute disease, during which the pathogen continues to multiply in the host and nonspecific signs and symptoms become observable
• proglottid body segment of a cestode (tapeworm)
• prokaryote an organism whose cell structure does not include a membrane-bound nucleus
• prokaryotic cell a cell lacking a nucleus bound by a complex nuclear membrane
• protists informal name for diverse group of eukaryotic organisms, including unicellular, colonial, and multicellular types that lack specialized tissues
• protozoan (plural: protozoa) a unicellular eukaryotic organism, usually motile
• protozoans informal term for some protists, generally those that are nonphotosynthetic, unicellular, and motile protozoology the study of protozoa
• provirus animal virus genome that has integrated into the host chromosome
• pseudohyphae short chains of yeast cells stuck together
• pseudomembrane grayish layer of dead cells, pus, fibrin, red blood cells, and bacteria that forms on mucous membranes
• pseudomembranous colitis inflammation of the large intestine with the formation of a pseudomembrane; caused by C. difficile
• pseudopodia temporary projections involved in ameboid movement; these “false feet” form by gel-sol cycling of actin polymerization/depolymerization
• psychrophile a microorganism that grows best at cold temperatures; most have an optimum growth temperature of about 15 °C and can survive temperatures below 0 °C; most cannot survive temperatures above 20 °C
• psychrotroph a microorganism that grows best at cool temperatures, typically between about 4 °C and 25 °C, with optimum growth at about 20 °C
• puerperal sepsis sepsis associated with a bacterial infection incurred by a woman during or after childbirth
• purulent an infection that produces pus; suppurative
• pus accumulation of dead pathogens, neutrophils, tissue fluid, and other bystander cells that may have been killed by phagocytes at the site of an infection
• pyelonephritis an infection of one or both kidneys
• pyoderma any suppurative (pus-producing) infection of the skin
• pyuria pus or white blood cells in the urine

Q

• quarantine the isolation of an individual for the purpose of preventing the spread of disease
• quaternary ammonium salts (quats) group of cationic detergents, named for the characteristic quaternary nitrogen atom that confers a positive charge, that make up an important class of disinfectants and antiseptics
• quinolines class of antiprotozoan drugs long used for the treatment of malaria
• quorum sensing cell-to-cell communication in bacteria; enables a coordinated response from cells when the population reaches a threshold density

R

• rabies contagious viral disease primarily transmitted by the bite of infected mammals that can cause acute encephalitis resulting in madness, aggressiveness, coma, and death
• reactivation tuberculosis secondary infection by Mycobacterium tuberculosis that forms later in life; occurs when the bacteria escape from the Ghon complexes and establish focal infections at other sites in immunocompromised individuals
• reactive oxygen species (ROS) unstable and toxic ions and molecules derived from partial reduction of oxygen
• receptor-mediated endocytosis a type of endocytosis in which extracellular ligands are targeted to specific cells through their binding to specific cell surface receptors
• redox potential tendency for a molecule to acquire electrons and become reduced; electrons flow from molecules with lower redox potentials to those with higher redox potentials
• redox reaction pairing of an oxidation reaction with a reduction reaction
• reduction reaction chemical reaction that adds electrons to acceptor molecules, leaving them reduced
• reemerging infectious disease a disease that was once under control or largely eradicated that has begun causing new outbreaks due to changes in susceptible populations, the environment, or the pathogen itself
• refraction bending of light waves, which occurs when a light wave passes from one medium to another
• rejection process by which adaptive immune responses recognize transplanted tissue as non-self, mounting a response that destroys the tissue or leads to the death of the individual
• replication process by which DNA is copied
• reservoir a living host or nonliving site in which a pathogenic organism can survive or multiply
• resident microbiota microorganisms that constantly live in the human body
• resolution the ability to distinguish between two points in an image
• retort large industrial autoclave used for moist heat sterilization on a large scale
• retrospective study a research design that associates historical data with present cases
• retrovirus positive ssRNA virus that produces and uses reverse transcriptase to make an ssDNA copy of the retroviral genome that can then be made into dsDNA and integrate into the host cell chromosome to form a provirus within the host chromosome.
• reverse transcriptase enzyme found in retroviruses that can make a copy of ssDNA from ssRNA
• reverse transcriptase inhibitor classes of antiviral drugs that involve nucleoside analog competitive inhibition and non-nucleoside noncompetitive inhibition of the HIV reverse transcriptase
• Reye syndrome potentially life-threatening sequelae to some viral infections that result in the swelling of the liver and brain; aspirin use has also been linked to this syndrome
• Rh factor red blood cell surface antigen that can trigger type II hypersensitivity reactions
• rheumatic fever serious clinical sequela of an infection with Streptococcus pyogenes that can result in damage to joints or the valves of the heart
• rheumatoid arthritis systemic autoimmune disease in which immune complexes form and deposit in the joints and their linings, leading to inflammation and destruction
• rhinitis inflammation of the nasal cavity
• ribosome a complex intracellular structure that synthesizes proteins
• rifampin semisynthetic member of the rifamycin class that blocks bacterial RNA polymerase activity, inhibiting transcription
• ringworm a tinea (cutaneous mycosis of the skin), typically characterized by a round, red, slightly raised lesion that heals outward from the center, giving it the appearance of a round worm
• rogue form misfolded form of the PrP protein that is normally found in the cell membrane and has the tendency to aggregate in neurons, causing extensive cell death and brain damage
• rubella German measles, caused by the rubella virus
• runs (running) purposeful, directional movement of a prokaryotic cell propelled by counterclockwise flagellar rotation

S

• salmonellosis gastrointestinal illness caused by Salmonella bacteria
• salpingitis inflammation of the fallopian tubes
• sanitization protocol that reduces microbial load on inanimate surfaces to levels deemed safe for public health
• SARS severe acute respiratory syndrome; caused by a zoonotic coronavirus that results in flu-like symptoms
• scarlet fever bacterial infection caused by Streptococcus pyogenes, marked by a high fever and a disseminated scarlet rash
• schistosomiasis helminthic infection caused by Schistosoma spp.; transmitted from a snail intermediate host to human
• scolex the head region of a cestode (tapeworm), which typically has suckers and/or hooks for attachment to the host
• scrapie form of transmissible spongiform encephalopathy that primarily affects sheep
• sebaceous gland a gland located in hair follicles that secretes sebum
• sebum lipid-rich substance secreted by the sebaceous glands of the skin
• secondary antibody antibody to which an enzyme is attached for use in ELISA assays; in direct and sandwich ELISAs, it is specific for the antigen being quantified, whereas in indirect ELISA, it is specific for the primary antibody
• secondary immunodeficiency impaired immune response due to infection, metabolic disturbance, poor diet, stress, or other acquired factors
• secondary infection second infection that develops after a primary infection as a result of the primary disease compromising immune defenses or antibiotics, thus eliminating protective microbiota
• secondary lymphoid tissue one of two types of lymphatic tissue; comprises the spleen, lymph nodes, Peyer’s patches, and mucosa associated lymphoid tissue (MALT)
• secondary response the adaptive immune response produced in response to a specific antigen to which the body has previously been exposed
• selective media media that contain additives that encourage the growth of some bacteria while inhibiting others
• selective toxicity desirable quality of an antimicrobial drug indicating that it preferentially kills or inhibits the growth of the target microbe while causing minimal or no harm to the host
• semicritical item object that contacts mucous membranes or nonintact skin but does not penetrate tissues; requires a high level of disinfection
• sepsis systemic inflammatory response to an infection that results in high fever and edema, causing organ damage and possibly leading to shock and death
• septic shock serious condition marked by the loss of blood pressure resulting from an inflammatory response against a systemic infection
• septic the condition of being septicemic; having an infection in the blood
• septicemia condition in which pathogens are multiplying in blood
• serial dilution sequential transfer of known volumes of culture samples from one tube to another to perform a several-fold dilution of the original culture
• sessile attached to a surface
• severe combined immunodeficiency disease (SCID) genetic disorder resulting in impaired function of B cells and T cells
• sex pilus specialized type of pilus that aids in DNA transfer between some prokaryotic cells
• shigellosis gastrointestinal illness caused by Shigella bacteria, also called bacillary dysentery
• shingles acute and painful rash that forms following the reactivation of a latent chickenpox infection
• shock extreme drop in blood pressure that, among other causes, can result from a strong immune response to the activity of toxins or response to bacterial products and can result in death
• sign objective and measurable indication of a disease
• simple microscope a type of microscope with only one lens to focus light from the specimen
• simple staining a staining technique that uses a single dye
• S-layer cell envelope layer composed of protein covering the cell walls of some bacteria and archaea; in some archaea, may function as the cell wall
• slime layer a type of glycocalyx with unorganized layers of polysaccharides that aid bacterial adherence to surfaces
• smear a thin layer of a specimen on a slide
• specificity the ability of the specific adaptive immune system to target specific pathogens or toxins
• spike viral glycoprotein embedded within the viral capsid or envelope used for attachment to host cells
• spirochetes a group of long, thin, spiral-shaped fastidious bacteria that includes the human pathogens that cause syphilis, Lyme disease, and leptospirosis
• spleen abdominal organ consisting of secondary lymphoid tissue that filters blood and captures pathogens and antigens that pass into it; also contains specialized macrophages and dendritic cells that are crucial for antigen presentation
• spontaneous generation the now-disproven theory that life can arise from nonliving matter
• sporadic disease an illness that occurs at relatively low levels with no discernible pattern or trend, frequently with no geographic focus
• sporulation the process by which a vegetative cell produces a dormant endospore
• spread plate method a technique used for inoculating plates with diluted bacterial samples for the purpose of cell counting; the liquid sample is pipetted onto solid medium and spread uniformly across the plate
• stage the platform of a microscope on which slides are placed
• staining the addition of stains or dyes to a microscopic specimen for the purpose of enhancing contrast
• staphylococcal food poisoning gastrointestinal illness caused by toxins produced by Staphylococcus aureus
• staphylolysins a class of staphylococcal exotoxins that are cytotoxic to skin cells and white blood cells
• stationary phase interval during which the number of cells formed by cell division is equal to the number of cells dying
• sterilant strong chemical that effectively kills all microbes and viruses in or on an inanimate item
• sterile field specified area that is free of all vegetative microbes, endospores, and viruses
• sterilization protocol that completely removes all vegetative cells, endospores, and viruses from an item
• strep throat (streptococcal pharyngitis) bacterial pharyngitis caused by Streptococcus pyogenes
• streptococcal toxic shock-like syndrome (STSS) condition similar to staphylococcal toxic shock syndrome but with greater likelihood of bacteremia, necrotizing fasciitis, and acute respiratory distress syndrome
• subclinical disease disease that does not present any signs or symptoms
• subcutaneous mycosis any fungal infection that penetrates the epidermis and dermis to enter deeper tissues
• substrate chemical reactants of an enzymatic reaction
• substrate-level phosphorylation direct method of ATP production in which a high-energy phosphate group is removed from an organic molecule and added to an ADP molecule
• subunit vaccine vaccine that contains only key antigens as opposed to whole pathogens
• sulfonamides (sulfa drugs) group of structurally related synthetic antimicrobial compounds that function as antimetabolites, competitively inhibiting an enzyme in the bacterial folic acid synthesis pathway
• superantigen class of exotoxin that triggers a strong nonspecific immune response with excessive production of cytokines (cytokine storm) causing inflammation, high fever, shock, and, potentially, death
• superinfection secondary infection that may develop as a result of long-term, broad-spectrum antimicrobial use
• superoxide dismutase enzyme that catalyzes the breakdown of superoxide anions
• surfactant group of chemical compounds used for degerming; lower the surface tension of water, creating emulsions that mechanically carry away microorganisms
• symbiosis any interaction between different species that are associated with each other within a community
• symptom subjective experience of disease felt by the patient
• syndrome group of signs and symptoms characteristic of a particular disease
• syphilis an STI caused by the bacterium Treponema pallidum
• systemic autoimmune disease autoimmune disease that affect the organism as a whole, rather than a single organ
• systemic infection infection that has spread to multiple locations or body systems
• systemic inflammatory response syndrome (SIRS) severe inflammatory response to the presence of microbes in the blood; can lead to sepsis
• systemic lupus erythematosus (SLE) systemic autoimmune disease producing inflammatory type III hypersensitivities as antibodies form immune complexes with nuclear and cytoplasmic antigens
• systemic mycosis a fungal infection that spreads throughout the body

T

• T-cell receptors (TCR) molecules on T cells involved in the recognition of processed foreign epitopes presented with MHC I or MHC II
• T lymphocyte lymphocyte that serves as the central orchestrator, bridging humoral, cellular, and innate immunity, and serves as the effector cells of cellular immunity; T cell
• taeniasis infection caused by Taenia
• tapeworms segmented, hermaphroditic, parasitic flatworms (Platyhelminthes)
• T-dependent antigen a protein antigen that is only capable of activating a B cell with the cooperation of a helper T cell
• telomerase enzyme that attaches to the end of a linear chromosome and adds nucleotides to the 3’ end of one of the DNA strands, maintaining the telomere sequence, thus preventing loss of DNA from the end of the chromosome
• telomere repetitive, noncoding sequence found at the end of a linear eukaryotic chromosome that protects the genes near the end of the chromosome from deletion as the DNA molecule is repeatedly replicated
• tetanus bacterial disease caused by exotoxin produced by Clostridium tetani that causes a rigid paralysis
• tetracyclines class of protein synthesis inhibitors that bind to the 30S subunit, blocking the association of tRNAs with the ribosome during translation
• T_H1 cells subtype of T cells that stimulate cytotoxic T cells, macrophages, neutrophils, and NK cells
• T_H2 cells subtype of T cells that stimulate B cells and direct their differentiation; also involved in directing antibody class switching
• thermophile a microorganism that grows best at warm temperatures, typically between about 50 °C and 80 °C
• thioglycolate medium medium designed to test the aerotolerance of bacteria; it contains a low concentration of agar to allow motile bacteria to move throughout the medium
• thioglycolate tube culture contains reducing medium through which oxygen diffuses from the tube opening, producing a range of oxygen environments down the length of the tube
• thrombocytes see platelets
• thymic selection a three-step process of negative and positive selection of T cells in the thymus
• tincture solution of an antiseptic compound dissolved in alcohol
• T-independent antigen a nonprotein antigen that can activate a B cell without cooperation from a helper T cell
• tinea any cutaneous fungal infection caused by dermatophytes, such as tinea corporis, tinea capitis, tinea cruris, and tinea pedis
• tinea capitis cutaneous mycosis of the scalp; also known as ringworm of the scalp
• tinea corporis cutaneous mycosis of the body; also known as ringworm of the body
• tinea cruris cutaneous mycosis of the groin region; also known as jock itch
• tinea pedis cutaneous mycosis of the feet; also known as athlete’s foot
• tissue tropism tendency of most viruses to infect only certain tissue types within a host
• tolerance lack of an anti-self immune response
• toll-like receptors (TLRs) pathogen recognition receptors (PRRs) that may be found on the external surface of phagocytes or facing inward in interior compartments
• tonsillitis inflammation of the tonsils
• total magnification in a light microscope is a value calculated by multiplying the magnification of the ocular by the magnification of the objective lenses
• toxemia presence of toxins in the blood
• toxic shock syndrome severe condition marked by the loss of blood pressure and blood clot formation caused by a bacterial superantigen, toxic shock syndrome toxin
• toxigenicity ability of a pathogen to produce toxins to cause damage to host cells
• toxin poison produced by a pathogen
• toxoid vaccine vaccine that contains inactivated bacterial toxins
• toxoplasmosis typically asymptomatic protozoan infection caused by Toxoplasma spp. and transmitted through contact with cysts in cat feces; infections in pregnant women may cause birth defects or miscarriage
• trace element indispensable element present in cells in lower amounts than macronutrients; also called micronutrient
• transcription process of synthesizing RNA using the information encoded in DNA
• transduction mechanism of horizontal gene transfer in bacteria in which genes are transferred through viral infection
• transformation mechanism of horizontal gene transfer in bacteria in which naked environmental DNA is taken up by a bacterial cell
• transient microbiota microorganisms, sometimes pathogenic, that are only temporarily found in the human body
• transition reaction reaction linking glycolysis to the Krebs cycle, during which each pyruvate is decarboxylated and oxidized (forming NADH), and the resulting two-carbon acetyl group is attached to a large carrier molecule called coenzyme A, resulting in the formation of acetyl-CoA and CO; also called the bridge reaction
• translation (protein synthesis) process of protein synthesis whereby a ribosome decodes an mRNA message into a polypeptide product
• transmissible spongiform encephalopathy degenerative disease caused by prions; leads to the death of neurons in the brain
• transmittance the amount of light that passes through a medium
• transparency the property of allowing light to pass through
• tricarboxylic acid cycle see Krebs cycle
• trophozoite a life cycle phase in which protists are actively feeding and growing
• tubercle small, rounded lesion
• tuberculosis life-threatening form of microbial infection marked by the presence of acid-fast bacteria growing in nodules (especially in the lungs)
• tumbles (tumbling) random, circuitous movement of a bacterial cell, propelled by clockwise flagellar rotation
• tumor collection or aggregate of cells; can be benign (noncancerous) or malignant (cancerous)
• turbidity cloudiness of a culture due to refraction of light by cells and particles
• type 1 diabetes mellitus hyperglycemia caused by an autoimmune disease affecting insulin production by β cells of the pancreas
• type I hypersensitivity rapid-onset allergic reaction due to cross-linking of antigen-specific IgE on the outside of mast cells, resulting in release of inflammatory mediators
• type II hypersensitivity cytotoxic reaction triggered by IgG and IgM antibodies binding to antigens on cell surfaces
• type III hypersensitivity inflammatory reaction induced by formation of immune complexes and their deposition in tissues and blood vessels
• type IV hypersensitivity delayed T-cell-mediated inflammatory reaction that takes longer to manifest than the first three hypersensitivity types, due to the need for activation of antigen-presenting cell and T-cell subsets
• typhoid fever serious illness caused by infection with certain serotypes of Salmonella

U

• UHT pasteurization method of pasteurization that exposes milk to ultra-high temperatures (near 140 °C) for a few seconds, effectively sterilizing it so that it can be sealed and stored for long periods without refrigeration
• ulcer open sore
• ureter duct that transports urine from the kidneys to the urinary bladder
• ureteritis inflammation of the ureter
• urethra duct through which urine passes from the urinary bladder to leave the body through the urinary meatus
• urethritis inflammation of the urethra

V

• vaccination inoculation of a patient with attenuated pathogens or antigens to activate adaptive immunity and protect against infection
• vaginitis inflammation of the vagina
• vaginosis an infection of the vagina caused by overgrowth of resident bacteria
• variolation the historical practice of inoculating a healthy patient with infectious material from a person infected with smallpox in order to promote immunity to the disease
• vasculitis inflammation affecting blood vessels (either arteries or veins)
• vector animal (typically an arthropod) that transmits a pathogen from one host to another host; DNA molecules that carry DNA fragments from one organism to another
• vegetative cell a cell that is actively growing and dividing, and does not contain an endospore
• vehicle transmission transfer of a pathogen between hosts via contaminated food, water, or air
• vertical direct transmission transfer of a pathogen from mother to child during pregnancy, birth, or breastfeeding
• vertical gene transfer transfer of genes from parent to offspring
• viable cell live cell; live cells are usually detected as colony-forming units
• viable plate count direct method of measuring microbial growth in a culture; the number of viable or live cells is usually expressed in CFU/mL
• viral envelope lipid membrane obtained from phospholipid membranes of the cell that surrounds the capsid
• viremia presence of virus in blood
• viricide chemical or physical treatment that destroys or inactivates viruses
• virion inert particle that is the reproductive form of a virus
• virology the study of viruses
• virulence degree to which an organism is pathogenic; severity of disease signs and symptoms
• virulence factor product of a pathogen that assists in its ability to cause infection and disease
• virus an acellular microorganism, consisting of proteins and genetic material (DNA or RNA), that can replicate itself by infecting a host cell

W

• West African trypanosomiasis chronic form of African trypanosomiasis caused by Trypanosoma brucei gambiense
• wet mount a slide preparation technique in which a specimen is placed on the slide in a drop of liquid
• wheal-flare reaction localized type I hypersensitivity reaction, involving a raised, itchy bump (wheal) and redness (flare), to injected allergen
• whooping cough common name for pertussis
• wild type phenotype of an organism that is most commonly observed in nature
• World Health Organization (WHO) international public health organization within the United Nations; monitors and communicates international public health information and coordinates international public health programs and emergency interventions

X

Y

• yeast any unicellular fungus
• yeast infection fungal infection of the vagina typically caused by an overgrowth of resident Candida spp.

Z

• zone of inhibition clear zone around a filter disk impregnated with an antimicrobial drug, indicating growth inhibition due to the antimicrobial drug
• zoonosis see zoonotic disease
• zoonotic disease any disease that is transmitted to humans by animals