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A Terms

AB toxins

The structure and activity of many exotoxins are based on the AB model. In this model, the B portion of the toxin is responsible for toxin binding to a cell but does not directly harm it. The A portion enters the cell and disrupts its function.
(See page(s) 797)

accessory pigments

Photosynthetic pigments such as carotenoids and phycobiliproteins that aid chlorophyll in trapping light energy.
(See page(s) 196)

acetyl coenzyme A (acetyl-CoA)

A combination of acetic acid and coenzyme A that is energy rich; it is produced by many catabolic pathways and is the substrate for the tricarboxylic acid cycle, fatty acid biosynthesis, and other pathways.
(See page(s) 183)

acid dyes

Dyes that are anionic or have negatively charged groups such as carboxyls.
(See page(s) 27)

acid fast

Refers to bacteria like the mycobacteria that cannot be easily decolorized with acid alcohol after being stained with dyes such as basic fuchsin.
(See page(s) 543)

acid-fast staining

A staining procedure that differentiates between bacteria based on their ability to retain a dye when washed with an acid alcohol solution.
(See page(s) 28)

acidophile

A microorganism that has its growth optimum between about pH 0 and 5.5.
(See page(s) 123)

acquired enamel pellicle

A membranous layer on the tooth enamel surface formed by selectively adsorbing glycoproteins (mucins) from saliva. This pellicle confers a net negative charge to the tooth surface.
(See page(s) 934)

acquired immune deficiency syndrome (AIDS)

(AIDS) An infectious disease syndrome caused by the human immunodeficiency virus and is characterized by the loss of a normal immune response, followed by increased susceptibility to opportunistic infections and an increased risk of some cancers.
(See page(s) 878)

acquired immune tolerance

The ability to produce antibodies against nonself antigens while "tolerating" (not producing antibodies against) self-antigens.(See page(s) 758)

acquired immunity

Refers to the type of specific immunity that develops after exposure to a suitable antigen or is produced after antibodies are transferred from one individual to another.
(See page(s) 729)

actinobacteria

A group of gram-positive bacteria containing the actinomycetes and their high G 1 C relatives.
(See page(s) 541)

actinomycete

An aerobic, gram-positive bacterium that forms branching filaments (hyphae) and asexual spores.
(See page(s) 537)

actinorhizae

Associations between actinomycetes and plant roots.
(See page(s) 682)

activated sludge

Solid matter or sediment composed of actively growing microorganisms that participate in the aerobic portion of a biological sewage treatment process. The microbes readily use dissolved organic substrates and transform them into additional microbial cells and carbon dioxide.
(See page(s) 659)

activation energy

The energy required to bring reacting molecules together to reach the transition state in a chemical reaction.
(See page(s) 162)

active carrier

An individual who has an overt clinical case of a disease and who can transmit the infection to others.
(See page(s) 854)

active immunization

The induction of active immunity by natural exposure to a pathogen or by vaccination.
(See page(s) 764)

active site

The part of an enzyme that binds the substrate to form an enzyme-substrate complex and catalyze the reaction. Also called the catalytic site.
(See page(s) 162)

active transport

The transport of solute molecules across a membrane against an electrochemical gradient; it requires a carrier protein and the input of energy.
(See page(s) 101)

acute carrier

See casual carrier.
(See page(s) 854) An individual who harbors an infectious organism for only a short period.
(See page(s) 854)

acute infections

Virus infections with a fairly rapid onset that last for a relatively short time.
(See page(s) 410)

acute viral gastroenteritis

An inflammation of the stomach and intestines, normally caused by Norwalk and Norwalklike viruses, other caliciviruses, rotaviruses, and astroviruses.
(See page(s) 891)

acyclovir

A synthetic purine nucleoside derivative with antiviral activity against herpes simplex virus.
(See page(s) 821)

adenine

A purine derivative, 6-aminopurine, found in nucleosides, nucleotides, coenzymes, and nucleic acids.
(See page(s) 217)

adenosine diphosphate

The nucleoside diphosphate usually formed upon the breakdown of ATP when it provides energy for work.
(See page(s) 155)

adenosine 5_-triphosphate (ATP)

The triphosphate of the nucleoside adenosine, which is a high energy molecule or has high phosphate group transfer potential and serves as the cell's major form of energy currency.

adhesin

A molecular component on the surface of a microorganism that is involved in adhesion to a substratum or cell. Adhesion to a specific host tissue usually is a preliminary stage in pathogenesis, and adhesins are important virulence factors.
(See page(s) 792)

adjuvant

Material added to an antigen to increase its immunogenicity. Common examples are alum, killed Bordetella pertussis, and an oil emulsion of the antigen, either alone (Freund's incomplete adjuvant) or with killed mycobacteria (Freund's complete adjuvant).
(See page(s) 741)

adult T-cell leukemia

A type of white blood cell cancer caused by the HTLV-1 virus.
(See page(s) 887)

aerobe

An organism that grows in the presence of atmospheric oxygen.
(See page(s) 127)

aerobic anoxygenic photosynthesis

Photosynthetic process in which electron donors such as organic matter or sulfide, which do not result in oxygen evolution, are used under aerobic conditions.
(See page(s) 614)

aerobic respiration

A metabolic process in which molecules, often organic, are oxidized with oxygen as the final electron acceptor. 154,
(See page(s) 173)

aerotolerant anaerobes

Microorganisms that grow equally well whether or not oxygen is present.
(See page(s) 127)

aflatoxin

A polyketide secondary fungal metabolite that can cause cancer.
(See page(s) 967)

agar

A complex sulfated polysaccharide, usually extracted from red algae, that is used as a solidifying agent in the preparation of culture media.
(See page(s) 105)

agglutinates

The visible aggregates or clumps formed by an agglutination reaction.
(See page(s) 775)

agglutination reaction

The formation of an insoluble immune complex by the cross-linking of cells or particles.
(See page(s) 756)

agglutinin

The antibody responsible for an agglutination reaction.
(See page(s) 756)

AIDS-related complex (ARC)

A collection of symptoms such as lymphadenopathy (swollen lymph glands), fever, malaise, fatigue, loss of appetite, and weight loss. It results from an HIV infection and may progress to frank AIDS.
(See page(s) 879)

airborne transmission

The type of infectious organism transmission in which the pathogen is truly suspended in the air and travels over a meter or more from the source to the host.
(See page(s) 854)

akinetes

Specialized, nonmotile, dormant, thick-walled resting cells formed by some cyanobacteria.
(See page(s) 473)

alcoholic fermentation

A fermentation process that produces ethanol and CO2 from sugars.
(See page(s) 179)

alga

A common term for a series of unrelated groups of photosynthetic eucaryotic microorganisms lacking multicellular sex organs (except for the charophytes) and conducting vessels.
(See page(s) 571)

algicide

An agent that kills algae.
(See page(s) 138)

algology

The scientific study of algae.
(See page(s) 571)

alkalophile

A microorganism that grows best at pHs from about 8.5 to 11.5.
(See page(s) 123)

allergen

A substance capable of inducing allergy or specific susceptibility.
(See page(s) 768)

allergic contact dermatitis

An allergic reaction caused by haptens that combine with proteins in the skin to form the allergen that produces the immune response.
(See page(s) 771)

allergy

See hypersensitivity.
(See page(s) 768) A condition of increased immune sensitivity in which the body reacts to an antigen with an exaggerated immune response that usually harms the individual. Also termed an allergy.
(See page(s) 768)

allograft

A transplant between genetically different individuals of the same species.
(See page(s) 773)

allosteric enzyme

An enzyme whose activity is altered by the binding of a small effector or modulator molecule at a regulatory site separate from the catalytic site; effector binding causes a conformational change in the enzyme and its catalytic site, which leads to enzyme activation or inhibition.
(See page(s) 165)

allotype

Allelic variants of antigenic determinant(s) found on antibody chains of some, but not all, members of a species, which are inherited as simple Mendelian traits.
(See page(s) 734)

alpha hemolysis

A greenish zone of partial clearing around a bacterial colony growing on blood agar.
(See page(s) 531, 797)

alpha-proteobacteria

One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. This group contains most of the oligotrophic proteobacteria; some have unusual metabolic modes such as methylotrophy, chemolithotrophy, and nitrogen fixing ability. Many have distinctive morphological features.
(See page(s) 487)

alternative complement pathway

An antibody-independent pathway of complement activation that includes the C3-C9 components of the classical pathway and several other serum protein factors (e.g., factor B and properdin).
(See page(s) 716)

alveolar macrophage

A vigorously phagocytic macrophage located on the epithelial surface of the lung alveoli where it ingests inhaled particulate matter and microorganisms.
(See page(s) 711)

amantadine (ah-man_tah-den)

An antiviral compound used to prevent type A influenza infections.
(See page(s) 821)

amebiasis

An infection with amoebae, often resulting in dysentery; usually it refers to an infection by Entamoeba histolytica.
(See page(s) 950)

amensalism

A relationship in which the product of one organism has a negative effect on another organism.
(See page(s) 609)

American trypanosomiasis (Chagas' disease)

See trypanosomiasis.
(See page(s) 957) A protozoan of the genus Trypanosoma. Trypanosomes are parasitic flagellate protozoa that often live in the blood of humans and other vertebrates and are transmitted by insect bites.
(See page(s) 589, 957)

Ames test

A test that uses a special Salmonella strain to test chemicals for mutagenicity and potential carcinogenicity.
(See page(s) 253)

amino acid activation

The initial stage of protein synthesis in which amino acids are attached to transfer RNA molecules.
(See page(s) 266)

aminoacyl or acceptor site (A site)

The site on the ribosome that contains an aminoacyl-tRNA at the beginning of the elongation cycle during protein synthesis; the growing peptide chain is transferred to the aminoacyl-tRNA and lengthens by an amino acid.
(See page(s) 270)

aminoglycoside antibiotics

A group of antibiotics synthesized by Streptomyces and Micromonospora, which contain a cyclohexane ring and amino sugars; all aminoglycoside antibiotics bind to the small ribosomal subunit and inhibit protein synthesis.
(See page(s) 816)

amnesic shellfish poisoning

The disease arising in humans and animals that eat seafood such as mussels contaminated with domoic acid from diatoms. The disease produces short-term memory loss in its victims.
(See page(s) 580)

amoeboid movement

Moving by means of cytoplasmic flow and the formation of pseudopodia (temporary cytoplasmic protrusions of the cytoplasm).
(See page(s) 590)

amphibolic pathways

Metabolic pathways that function both catabolically and anabolically.
(See page(s) 176)

amphitrichous

A cell with a single flagellum at each end.
(See page(s) 63)

amphotericin B

An antibiotic from a strain of Streptomyces nodosus that is used to treat systemic fungal infections; it also is used topically to treat candidiasis.
(See page(s) 820)

anabolism

The synthesis of complex molecules from simpler molecules with the input of energy.
(See page(s) 173)

anaerobe

(an-a_er-øob) An organism that grows in the absence of free oxygen.
(See page(s) 127)

anaerobic digestion

The microbiological treatment of sewage wastes under anaerobic conditions to produce methane.
(See page(s) 659)

anaerobic respiration

An energy-yielding process in which the electron transport chain acceptor is an inorganic molecule other than oxygen.
(See page(s) 173)

anammox process

The coupled use of nitrite as an oxidant and ammonium ion as a reductant under anaerobic conditions to yield nitrogen gas.
(See page(s) 616)

anamnestic response

The recall, or the remembering, by the immune system of a prior response to a given antigen.
(See page(s) 729, 743)

anaphylaxis

An immediate (type I) hypersensitivity reaction following exposure of a sensitized individual to the appropriate antigen. Mediated by reagin antibodies, chiefly IgE.
(See page(s) 768)

anaplerotic reactions

Reactions that replenish depleted tricarboxylic acid cycle intermediates.
(See page(s) 216)

anergy

A state of unresponsiveness to antigens. Absence of the ability to generate a sensitivity reaction to substances that are expected to be antigenic.
(See page(s) 758)

annotation

The process of determining the location of specific genes in a genome map after it has been produced by nucleic acid sequencing.
(See page(s) 347)

anogenital condylomata (venereal warts)

Warts that are sexually transmitted and caused by types 6, 11, and 42 human papillomavirus. Usually occur around the cervix, vulva, perineum, anus, anal canal, urethra, or glans penis.
(See page(s) 894)

anoxygenic photosynthesis

Photosynthesis that does not oxidize water to produce oxygen; the form of photosynthesis characteristic of purple and green photosynthetic bacteria.
(See page(s) 199, 468)

antheridium

A male gamete-producing organ, which may be unicellular or multicellular.
(See page(s) 561, 574)

anthrax

An infectious disease of animals caused by ingesting Bacillus anthracis spores. Can also occur in humans and is sometimes called woolsorter's disease.
(See page(s) 913)

antibiotic

A microbial product or its derivative that kills susceptible microorganisms or inhibits their growth.
(See page(s) 806)

antibody (immunoglobulin)

A glycoprotein produced in response to the introduction of an antigen; it has the ability to combine with the antigen that stimulated its production. Also known as an immunoglobulin (Ig).
(See page(s) 734)

antibody-dependent cell-mediated cytotoxicity (ADCC)

The killing of antibody-coated target cells by cells with Fc receptors that recognize the Fc region of the bound antibody. Most ADCC is mediated by NK cells that have the Fc receptor or CD16 on their surface.
(See page(s) 723)

antibody-mediated immunity

See humoral immunity.
(See page(s) 729) The type of immunity that results from the presence of soluble antibodies in blood and lymph; also known as antibody-mediated immunity.
(See page(s) 729)

antigen

A foreign (nonself) substance (such as a protein, nucleoprotein, polysaccharide, or sometimes a glycolipid) to which lymphocytes respond; also known as an immunogen because it induces the immune response.
(See page(s) 731)

antigen-binding fragment (Fab)

"Fragment antigen binding." A monovalent antigen-binding fragment of an immunoglobulin molecule that consists of one light chain and part of one heavy chain, linked by interchain disulfide bonds.
(See page(s) 734)

antigenic determinant site (epitope)

See epitope.
(See page(s) 731) An area of the antigen molecule that stimulates the production of, and combines with, specific antibodies; also known as the antigenic determinant site.
(See page(s) 731)

antigenic drift

A small change in the antigenic character of an organism that allows it to avoid attack by the immune system.
(See page(s) 852)

antigenic shift

A major change in the antigenic character of an organism that alters it to an antigenic strain unrecognized by host immune mechanisms.
(See page(s) 852)

antigen-presenting cells

Antigen-presenting cells (APCs) are cells that take in protein antigens, process them, and present antigen fragments to B cells and T cells in conjunction with class II MHC molecules so that the cells are activated. Macrophages, B cells, dendritic cells, and Langerhans cells may act as APCs.
(See page(s) 745)

antimetabolite

A compound that blocks metabolic pathway function by competitively inhibiting a key enzyme's use of a metabolite because it closely resembles the normal enzyme substrate.
(See page(s) 812)

antimicrobial agent

An agent that kills microorganisms or inhibits their growth.
(See page(s) 139)

antisense RNA

A single-stranded RNA with a base sequence complementary to a segment of another RNA molecule that can specifically bind to the target RNA and inhibit its activity.
(See page(s) 283)

antisepsis

antisepsis (an²tùõ-sep_sis) The prevention of infection or sepsis.
(See page(s) 138)

antiseptic

Chemical agents applied to tissue to prevent infection by killing or inhibiting pathogens.
(See page(s) 138)

antiserum

Serum containing induced antibodies.
(See page(s) 742)

antitoxin

An antibody to a microbial toxin, usually a bacterial exotoxin, that combines specifically with the toxin, in vivo and in vitro, neutralizing the toxin.
(See page(s) 756, 796)

apical complex

A set of organelles characteristic of members of the phylum Apicomplexa: polar rings, subpellicular microtubules, conoid, rhoptries, and micronemes.
(See page(s) 591)

apicomplexan

A sporozoan protist that lacks special locomotor organelles but has an apical complex and a spore-forming stage. It is either an intra- or extracellular parasite of animals; a member of the phylum Apicomplexa.
(See page(s) 591)

aplanospore

A nonflagellated, nonmotile spore that is involved in asexual reproduction.
(See page(s) 573)

apoenzyme

The protein part of an enzyme that also has a nonprotein component.
(See page(s) 161)

apoptosis

Programmed cell death. The fragmentation of a cell into membrane-bound particles that are eliminated by phagocytosis. Apoptosis is a physiological suicide mechanism that preserves homeostasis and occurs during normal tissue turnover. It is responsible for cell death in pathological circumstances, such as exposure to low concentrations of xenobiotics and infections by HIV and various other viruses. Apoptotic cells display profound structural changes such as plasma membrane blebbing and nuclear collapse. DNA is cleaved into short oligonucleosomal length DNA fragments. Apoptosis usually occurs after the activation ofr calcium-dependent endogenous endonuclease.
(See page(s) 750, 881)

aporepressor

An inactive form of the repressor protein, which becomes the active repressor when the corepressor binds to it.
(See page(s) 276)

arbuscular mycorrhizal (AM) fungi

The mycorrhizal fungi in a symbiotic fungus-root association that penetrate the outer layer of the root, grow intracellularly, and form characteristic much-branched hyphal structures called arbuscules.
(See page(s) 681)

arbuscules

Branched, treelike structures formed in cells of plant roots colonized by endotrophic mycorrhizal fungi.
(See page(s) 681)

Archaea

The domain that contains procaryotes with isoprenoid glycerol diether or diglycerol tetraether lipids in their membranes and archaeal rRNA (among many differences).
(See page(s) 424, 451)

arthroconidium

A thallic conidium released by the fragmentation or lysis of hypha. It is not notably larger than the parental hypha, and separation occurs at a septum.
(See page(s) 557)

arthrospore

A spore resulting from the fragmentation of a hypha.
(See page(s) 557)

artificially acquired active immunity

The type of immunity that results from immunizing an animal with a vaccine. The immunized animal now produces its own antibodies and activated lymphocytes.
(See page(s) 730)

artificially acquired passive immunity

The type of immunity that results from introducing into an animal antibodies that have been produced either in another animal or by in vitro methods. Immunity is only temporary.
(See page(s) 731)

ascocarp

A multicellular structure in ascomycetes lined with specialized cells called asci in which nuclear fusion and meiosis produce ascospores. An ascocarp can be open or closed and may be referred to as a fruiting body.
(See page(s) 561)

ascogenous hypha

A specialized hypha that gives rise to one or more asci.
(See page(s) 561)

ascogonium

The receiving (female) organ in ascomycetous fungi which, after fertilization, gives rise to ascogenous hyphae and later to asci and ascospores.
(See page(s) 561)

ascomycetes

A division of fungi that form ascospores.
(See page(s) 560)

ascospore

A spore contained or produced in an ascus.
(See page(s) 558)

ascus

A specialized cell, characteristic of the ascomycetes, in which two haploid nuclei fuse to produce a zygote, which immediately divides by meiosis; at maturity an ascus will contain ascospores.
(See page(s) 561)

aseptic meningitis syndrome

See meningitis.
(See page(s) 902) A condition that refers to inflammation of the brain or spinal cord meninges (membranes). The disease can be divided into bacterial (septic) meningitis (caused by bacteria) and aseptic meningitis syndrome (caused by nonbacterial sources).
(See page(s) 902)

aspergillosis

A fungal disease caused by species of Aspergillus.
(See page(s) 948)

assimilatory reduction

The reduction of an inorganic molecule to incorporate it into organic material. No energy is made available during this process.
(See page(s) 210, 211, 614)

associative nitrogen fixation

Nitrogen fixation by bacteria in the plant root zone (rhizosphere).
(See page(s) 675)

athlete's foot

See tinea pedis.
(See page(s) 944) A fungal infection of the foot caused by Trichophyton rubrum, T. mentagrophytes, or E. floccosum; also known as athlete's foot.
(See page(s) 944)

atomic force microscope

A type of scanning probe microscope that images a surface by moving a sharp probe over the surface at a constant distance; a very small amount of force is exerted on the tip and probe movement is followed with a laser.
(See page(s) 38)

ATP-binding cassette transporters (ABC transporters)

Membrane protein complexes that use ATP energy to move substances across membranes without modifying the compound being transported. They require an extracytoplasmic substrate-binding protein for proper function.
(See page(s) 101)

attenuation

1. A mechanism for the regulation of transcription of some bacterial operons by aminoacyl-tRNAs. 2. A procedure that reduces or abolishes the virulence of a pathogen without altering its immunogenicity.
(See page(s) 281, 766)

attenuator

A rho-independent termination site in the leader sequence that is involved in attenuation.
(See page(s) 279)

autoclave

An apparatus for sterilizing objects by the use of steam under pressure. Its development tremendously stimulated the growth of microbiology.
(See page(s) 140)

autogenous infection

An infection that results from a patient's own microbiota, regardless of whether the infecting organism became part of the patient's microbiota subsequent to admission to a clinical care facility.
(See page(s) 866)

autoimmune disease

A disease produced by the immune system attacking self-antigens. Autoimmune disease results from the activation of self-reactive T and B cells that damage tissues after stimulation by genetic or environmental triggers.
(See page(s) 772)

autoimmunity

Autoimmunity is a condition characterized by the presence of serum autoantibodies and self-reactive lymphocytes. It may be benign or pathogenic. Autoimmunity is a normal consequence of aging; is readily inducible by infectious agents, organisms, or drugs; and is potentially reversible in that it disappears when the offending "agent" is removed or eradicated.
(See page(s) 772)

autolysins

Enzymes that partially digest peptidoglycan in growing bacteria so that the peptidoglycan can be enlarged.
(See page(s) 223)

autotroph

An organism that uses CO2 as its sole or principal source of carbon.
(See page(s) 96)

auxotroph

A mutated prototroph that lacks the ability to synthesize an essential nutrient and therefore must obtain it or a precursor from its surroundings.
(See page(s) 245)

axial filament

The organ of motility in spirochetes. It is made of axial fibrils or periplasmic flagella that extend from each end of the protoplasmic cylinder and overlap in the middle of the cell. The outer sheath lies outside the axial filament.
(See page(s) 66, 479)

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