Microbiology terms - A

ABO blood group
Classification of red blood cells based on the presence or absence of A and B carbohydrate antigens.
abscess
A localized accumulation of pus due to infection.
acellular vaccine
Vaccine consisting of antigenic parts of cells.
acetoclastis
The process of splitting acetate into methane and carbon dioxide by s ome methanogens.
acetyl-CoA pathway
A pathway of autotrophic carbon dioxide fixa tion commonly happened in obligate anaerobes such as methanogens
, homoacetogens, and sulfate-reducing bacteria.
 
acetylene reduction assay
A method to determine the activity of nit rogenase. Instead of the natural substrate of nitrogenase, i.e. dinitrogen (N2), acetylene is provide d as the alternative substrate for this enzyme . Acetylene (C2H2) is reduced to ethylene (C2 H4) during the assay if there is nitrogenase activity. B oth substrate and product can be resolved by gas chromatography.
acid mine drainage
The process to draw off acidic water from natural mine rich of sulfid e minerals which has been oxidized to sulfuric acid by microbial actions.
acid-fast stain
A staining technique used to determine the cell wall property of an m icroorganism. After stained with dye such as hot carbolfuschin, an acid-f ast organism, (.e.g. Mycobacterium species) will retain the color in its cell wall after being washed with acid-alcohol.
acidophile
An organism that grows optimally at acidic (low) pH values (usually b elow 6, sometimes as low as 1) and grows poorly or not at all under highe r pH conditions (i.e. higher than 7).
actinomycetes
Gram-positive bacteria that can for m branching filaments. They may form true myceli a or produce conidiospores.
activation energy
Energy required to make substrate molec ules active enough for an reaction to occur. Catalysts and enzymes function by lowering the activation energy of the su bstrates during a chemical reaction.
activator
A regulatory protein that binds to specif ic sites on DNA and stimulates transcription; an activator is usually involved in the po sitive control of transcription regulation.
active immunity
Production of antibodies by the body's own im mune system due to the exposure to antigen. Compare with passive immunity.
active site
The region of an enzyme where substrate(s) bind(s) prior to the reaction occurs.
active transport
The energy-dependent process of transporting substances (e.g. nutrien ts, ions, waste products) into (uptake) or out of (efflux) the cell in which the transported substances are chemically un changed.
acute
Used to describe a short-term infection or disease which is characterized by dramatic onset and rapid recovery.
adherence
Refers to the ability of bacteria adhea r (stick) to host surfaces.
aerobe (adjective: aerobic)
An organism that grows in the presence of oxygen. There may be facultative or obligat e aerobes. Compare with anaerobe.
aerobic
An adjective used to describe an environment or a condition in which oxygen (O2) is present; an adjective to describe an organism w hich can grow in the presence of oxygen.
aerogenic
gas producing, e.g., aerogenic fermentation.
aerosol
A gaseous suspension of fine solid or liquid particles. In medical as pect, An aerosol released by sneezing or coughing, may contain viable mic robial particles such as microorganisms or viruses.
aerotolerant
Used to describe an anaerobe which will not be inhibited by oxygen and can still grow at sub-optimal rates.
agar
A complex polysaccharide which is widely used as a gelling agent used to prepare solid or semi-solid microbiological medium. Agar consists of about 70% of agarose and 30% of agaropectin. Agar can be melt at temperature above 100°C; gelling temperature is 40-50°C. Also called: agar agar.
agarose
A non-sulphated linear polymer consisting of alternating residues of D-galactose and 3,6-anhydro-L-galactose:

[-3,6-anhydro-alpha-L-galactopyranosyl-(1->3)-beta-D-galactopyranosyl-(1->4)-]n

Agarose is extracted from seaweed and is widely used as the resolving agent in electrophoresis (i.e. agarose gel electrophoresis).

agglutination
Aggregation formed by the combination of antibody and particle-bound antigen.
alga (plural algae)
Phototrophic eukaryotic microorganisms. Algae c ould be unicellular or multicellular. Blue-green algae is not true algae; it belongs to a group of bacteria called c yanobacteria because it lacks a nucleus i n the cell.
alkaliphile (also alkalophile)
An organism that grows optimally at high pH (alkaline conditions). Th e typical pH range for alkaliphiles is 8 - 11. They grow poorly or not at all at the pH below 7. Compare with acidophile .
allergy
A harmful immune reaction, either immediat e-type or delayed-type hypersensitivity caused by a foreign antigen (i.e. allergen) i n food, pollen, or chemicals.
allosteric
Used to describe some protein, especially enzymes, in which a compound combine with a site on the protein other than the active site. This may result in a conformational change at the active site so that the normal substrate can not bind to it. The a llosteric property is useful in the regulatiio n of enzyme activity.
amber mutation
The mutation due to the introduction of a stop codon (UAG) within the coding sequence of a gene which results in premature termination of translation.
amino acid
An organic acid containing an amino group (-NH2) and a carboxyl group (-COOH). Can be represented by the general formula: R-CH(NH2)COOH, in which R may be hydrogen or an organic group and determines the properties of the amino acid. Amino acids are building blocks of proteins.
amino group
-NH2
amoeba (or ameba, plural: amoebae)
Refers to any (eukaryotic) cell or orga nism which is able to alter its cell shape drastically, usually by the ex trusion of one or more pseudopodia.
Amoeba
A genus of free-living amoebae. Type species: Amoeba proteus.
amoeboid
Amoeba-like.
amoeboid movement
A type of motility in which cytoplasmic streaming extrudes outward of the cell to form pseudopodia) so that the cell can be relocated.
amplification
1. Increase of copy number of a plasmid by inhibiting the replication of chromosome while allowing plasmid replication to continue.

2. Increase of the number of copies of a gene either by duplication in the chromosome or by cloning into a plasmid vector. This is normally referred to as gene amplification.

anabolism
Refers to those metabolic processs involved in the synthesis of cell constituents from simpler molecules, such as org anic and/or inorganic precursors. An anabolic process usually requires energy.
anaerobe
An organism which has the ability to grow in the absence of oxygen. C ompare with aerobe. Also see facultative anaerobe.
anaerobic
An adjective used to describe an environment or a condition which is free of oxygen or to describe a microorganism which can grow in the absence of oxygen.
anaerobic respiration
Respiration under anaerobic conditions. The terminal electron acceptor, instead of oxygen in the case of regular respira tion, can be: CO2 , Fe2+, fumarate, nitrate, nitrite, nitrous oxide, sulphur, su lphate, etc. Note that anaerobic respiration still uses electron trasnport chain to dump the electron whil e ferementation does not.
anaerogenic
without forming gas, e.g., anaerogenic 4fermentation.
anaphylatoxins
The C3a and C5a fractions during complement fixation. They act to mim ic some of the reactions of anaphylaxis and ca n induce the release of histamine from mast cells. C5a is also chemotacti c for neutrophils and monocytes.
anaphylaxis (anaphylactic shock; type I reaction)
A strong allergic reaction caused by an antigen-antibody reaction (immediate hypersensitivity).
annealing
The process of formation of double-stranded DNA from single-stranded DNA; compare with hybridization.
anoxic (noun: anoxia)
Lack of oxygen. An adjective usually used to desribe a microbial habitat.
anoxygenic photosynthesis
A type of photosynthesis in green and purple bacteria in which oxygen is not produced. Use of light energy to synthesize ATP by cyclic photo phosphorylation without oxygen production in green and purple bacteri a.
antibiotic
A chemical compound produced by one microorganism (especially fungi) which can inhibit the growth of (or kill) other microorganisms. Antibiotics are used to treat infectious diseases. Examples of some commonly used antibiotics are: penicillin, streptomycin, and tetracycline. Inadequate use of antibiotics can lead to the developement of the resistance of the pathogens.
antibody
A protein present in serum or other body fl uid that combines specifically with antigen. An immunoglobulin.
anticodon
A sequence of three bases in tRNA that base pairs with a codon in mRNA.
antigen
A substance, usually macromolecular , that induces a specific immune response.
antigen-presenting cell (APC)
Cells that process and present antigen to T lymphocytes.
antigenic determinants
The portion of an antigen that interacts with an immunoglobulin or T cell receptor.
antigenic drift
In influenza virus, minor changes in viral proteins (antigens) due to gene mutation.
anti-metabolite
An analogue of the end-product of a metabolic pathway that causes feedback inhibition or repression, but cannot replace the genuine product; used for selecting feedback-deficient mutants.
antimicrobial
harmful to microorganisms by either killing or inhibiting growth.
antiparallel
In reference to double-stranded DNA, the orie ntation of the two strnads: one strand runs 5'-->3', the other 3'-->5'
antisense RNA
An sequence of RNA which is complementary to the mRNA. Anitsense RNA can usually interfere with translation process.
antiseptic
An agent that kills or inhibits microbial growth but is not harmful t o human tissue.
antiserum
A serum containing anti bodies.
anti-terminator
A protein that allows RN polymerase to read through a terminator.
antitoxin
An antibody that specifically interacts with and neutralizes a toxin
Archaea
An evolutionarily distinct group (domain) of prokayrotes consisting of the methanogens, most extreme halophiles and hyperthermophiles, and Thermoplasma.
archaebacteria
An older term for the Archaea.
aseptic technique
Manipulation of sterile instruments or cu lture media in such a way as to maintain sterility.
atomic weight
The average weight of an atom of an element, i.e. the total mass of p rotons and neutrons in an atom.
adenosine triphosphate (ATP)
The principal energy carrier of the cell.
attenuation
1. Reduction in the virulence of a pathogen; usually an attenuated pathogen is still cap able of immunizing.

2. A process that plays a role in the regulation of enzymes involved in amino acid biosynthesis.

autoantibody
Antibodies that react to self antigens.
autogenous control
The expression of a gene is regulated by its own gene product(s).
autoimmunity
Immune reactions of a host against its own self constituents.
autolysis
Spontaneous lysis.
autoradiography
Detection of radioactivity in a sample, for example a cell or gel, by placing it in contact with a photographic film (e.g. X-ray film).
autotroph
In reference to carbon source - an organism which uses carbon dioxide (CO2) as the sole carbon source. Compare with lithotroph, heterotroph, organotroph, and phototro ph.
auxotroph
A mutant that has a growth factor requirement. Contrast with a prototroph.

Compiled by Tsute Chen, Converted by Ben Hoyt