ABC transport systems A type of active transport system that requires ATP as an energy source (4TP Binding-Cassette).

abscess A localized collection of pus within a tissue. A-B toxin Exotoxin composed of an active subunit (A-sub-

unit) and a binding subunit (B-subunit). acellular Not composed of cells, therefore not living. acetyl-CoA Product of the transition reaction; a precursor metabolite used in fatty acid synthesis. acid-fast staining A procedure used to stain certain microorganisms, particularly members of the genus Mycobacterium, that do not readily take up dyes used in microbiology. acidic amino acids Amino acids with more carboxyl

(—COOH) than amino (—NH2) groups. acidophiles Organisms that grow optimally at a pH below 5.5.

acquired resistance Development of antimicrobial resistance in a previously sensitive organism; occurs through spontaneous mutation or acquisition of new genetic information.

acridine orange A fluorescent dye that binds DNA and can be used to determine the total number of microorganisms in a sample. actin Protein that makes up actin filaments of eukaryotic cells; it can rapidly assemble and subsequently disassemble to cause motion. actin filaments Cytosketelal structures of eukaryotic cells that enable the cell cytoplasm to move. actinomycetes Filamentous bacteria; many are valuable in the production of antibiotics. activated macrophages Macrophages stimulated by cytokines to enlarge and become metabolically active, with greatly increased capability to kill and degrade intracellular organisms and materials. activated sludge method A method of sewage treatment in which wastes are degraded by complex populations of aerobic microorganisms. activated T cell T cell activated by exposure to antigen in conjunction with required accessory signals. activation energy Initial energy required to break a chemical bond.

activator-binding site Sequence of DNA that precedes an ineffective promoter; binding of an activator to this site enhances the ability of RNA polymerase to initiate transcription at that promoter. active immunity Protective immunity produced by an individual in response to an antigenic stimulus. active site Site on an enzyme molecule to which substrate binds; also known as the catalytic site. active transport Energy-consuming process by which molecules are carried across cell boundaries; can accumulate compounds against a concentration gradient. acute infections Infections in which the symptoms and signs have a rapid onset and are usually severe, often with fever, but short-lived. acute inflammation Short-term inflammatory response, marked by a prevalence of neutrophils. acute phase response Changes in the blood that occur early during an infection, with the production of acute phase proteins and cells that contribute to the inflammatory response.

acylated homoserine lactone (AHL) Small molecules that can move freely in and out of a cell; provides cells with a mechanism of assessing cell density (quorum sensing).

adaptive immune response Immune response that depends on the recognition and elimination of antigens by antigen-specific lymphocytes. ADCC (antibody-dependent cellular cytotoxicity)

Killing of target cells by macrophages, granulocytes, or natural killer cells that contact the target via their Fc receptors binding to Fc of antibodies attached to the target.

adenosine diphosphate (ADP) The acceptor of free energy in a cell; that energy is used to add an inorganic phosphate (Pi) to ADP, generating ATP. adenosine triphosphate (ATP) The energy currency of a cell, serving as the ready and immediate donor of free energy.

adherence A necessary first step in colonization and infection, in which the pathogen attaches to host cells to avoid being removed from the body. adhesin Component of a microorganism that is used to bind to surfaces. adhesion molecule Molecule on the surface of a cell that allows that cell to adhere to other cells. adjuvant Substance that increases the immune response to antigen.

ADP Abbreviation for adenosine diphosphate. adsorption Attachment of one substance to the surface of another.

aerobic respiration Metabolic process in which electrons are transferred from the electron transport chain to molecular oxygen (O2). aerosol Material dispersed into the air as a fine mist. aerotaxis Movement toward or away from molecular oxygen.

aerotolerant anaerobes Organisms that can grow in the presence of O2 but never use it as a terminal electron acceptor; also called obligate fermenters. affinity maturation The "fine-tuning'' of the fit of an antibody molecule for an antigen; it is due to mutations that occur as activated B cells multiply. aflatoxin Potent toxin made by species of Aspergillus; may contaminate peanuts and other grains. agar Polysaccharide extracted from marine algae; used to solidify microbiological media. agarose Highly purified form of agar used in gel electrophoresis.

agar slant Microbiological medium that has been solidified with agar and stored in a tube that was held at a shallow angle as the medium solidified, creating a larger surface area.

agglutination Clumping together of cells or particles. AIDS Acquired immunodeficiency syndrome. AIDS-related complex (ARC) A group of symptoms, fever, fatigue, diarrhea, and weight loss, that herald the onset of AIDS.

alga (pl. algae) A primitive photosynthetic eukaryotic organism.

alkalophiles Organisms that grow optimally at a pH above 8.5.

alkylating agent Chemical that adds alkyl groups, short chains of carbon atoms, to purines and pyrimidines; promotes mutations. alkyl group Short chain or single carbon atom such as a methyl group (—CH3). allele One form of a gene. allergen Antigen that causes an allergy. allergic rhinitis Hay fever; sneezing, runny nose, teary eyes resulting from exposure of a sensitized person to inhaled antigen; an IgE-mediated allergic reaction. allergy Hypersensitivity, especially of the IgE-mediated type. allograft Organ or tissue graft transplanted between genetically nonidentical members of the same species. allosteric site Site on an allosteric enzyme that binds an effector molecule; binding alters the activity of the enzyme.

alpha (a) hemolysis Type of hemolysis observed on blood agar, characterized by zone of greenish clearing around the colonies.

alternative pathway Pathway of complement activation initiated by the binding of a complement protein (C3b) to cell surfaces. amalgam Mixture of mercury with other metals to form a paste that hardens; used to fill cavities in teeth. amino acids Subunits of a protein molecule. aminoglycosides Group of antimicrobial medications that interferes with protein synthesis. amino terminal (or N terminal) The end of the protein molecule that has an unbonded —NH2 group. ammonification The reactions that result in the release of ammonia (NH3) from organic nitrogen-containing molecules.

amphibolic pathways Metabolic pathways that play roles in both catabolism and anabolism. amylases Enzymes that digest starches. anabolism Cellular processes that use the energy stored in ATP to synthesize and assemble subunits such as amino acids; synonymous with biosynthesis. anaerobic Containing no molecular oxygen (O2). anaerobic respiration Metabolic process in which electrons are transferred from the electron transport chain to an inorganic terminal electron acceptor other than O2. analytical study An epidemiological study done to identify specific risk factors associated with developing a certain disease.

anamnestic response (See secondary response.) anaphylaxis Allergic reaction caused by IgE; generalized hypersensitive reaction to an allergen that can cause a profound drop in blood pressure. anapleurotic reactions Chemical reactions that bypass certain steps of the central metabolic pathways; they are used to replenish some of the intermediates drawn off for biosynthesis. anion Negatively charged ion.

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