Terms and Definitions

Here are some of the most common terms and definitions in microbiology science:
 Active immunization The induction of active immunity by natural exposure to a pathogen or by vaccination.
 Active transport The transport of solute molecules across a membrane against an electrochemical gradient; it requires a carrier protein and the input of energy.
 Acute infections Virus infections with a fairly rapid onset that last for a relatively short time.
 Agar A complex sulfated polysaccharide, usually extracted from red algae, that is used as a solidifying agent in the preparation of culture media.
 Alcoholic fermentation A fermentation process that produces ethanol and CO2 from sugars.
 Allergen A substance capable of inducing allergy or specific susceptibility.
 Antibiotic A microbial product or its derivative that kills susceptible microorganisms or inhibits their growth.
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.
 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.
 Bacillus A rod-shaped bacterium.
 Bacteremia The presence of viable bacteria in the blood.
 Bacteria The domain that contains procaryotic cells with primarily diacyl glycerol diesters in their membranes and with bacterial rRNA.
 Bacteria also is a general term for organisms that are composed of prokaryotic cells and are not multicellular.
 Cell cycle The sequence of events in a cell's growth-division cycle between the end of one division and the end of the next. In eukaryotic cells, it is composed of the G1 period, the S period in which DNA and histones are synthesized, the G2 period, and the M period (mitosis).
 Cell wall The strong layer or structure that lies outside the plasma membrane; it supports and protects the membrane and gives the cell shape.
 Cofactor The non-protein component of an enzyme; it is required for catalytic activity.
 Decomposer An organism that breaks down complex materials into simpler ones, including the release of simple inorganic products. Often a decomposer such as an insect or earthworm physically reduces the size of substrate particles.
 Delta agent A defective RNA virus that is transmitted as an infectious agent, but cannot cause disease unless the individual is also infected with the hepatitis B virus.
 F factor The fertility factor, a plasmid that carries the genes for bacterial conjugation and makes its E. coli host cell the gene donor during conjugation.
 Fluid mosaic model The currently accepted model of cell membranes in which the membrane is a lipid bilayer with integral proteins buried in the lipid, and peripheral proteins more loosely attached to the membrane surface.