A large group of single-cell microorganisms. Some cause infections and disease in animals and humans. The singular of bacteria is bacterium.

A unicellular, prokaryotic organism that reproduces by cell division and usually has cell walls; can be shaped like spheres, rods, or spirals; and can be found in virtually any environment.

Any organism assigned to the kingdom Bacteria.

One of the three domains of life (the others being Eukarya and ARCHAEA), also called Eubacteria. They are unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal. Bacteria can be classified by their response to OXYGEN: aerobic, anaerobic, or facultatively anaerobic; by the mode by which they obtain their energy: chemotrophy (via chemical reaction) or PHOTOTROPHY (via light reaction); for chemotrophs by their source of chemical energy: CHEMOLITHOTROPHY (from inorganic compounds) or chemoorganotrophy (from organic compounds); and by their source for CARBON; NITROGEN; etc.; HETEROTROPHY (from organic sources) or AUTOTROPHY (from CARBON DIOXIDE). They can also be classified by whether or not they stain (based on the structure of their CELL WALLS) with CRYSTAL VIOLET dye: gram-negative or gram-positive.

Tiny single-celled organisms. Some bacteria cause disease, although most are harmless.

Unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms, round or coccal, rodlike or bacillary, and spiral or spirochetal; bacteria can be classifed by their response to oxygen: aerobic, anerobic, or facultatively anerobic; by the mode by which they obtain energy: chemotrophic or phototrophic; for chemotrophs by their source of chemical energy: lithotrophic (from inorganic compounds) or organotrophic (from organic compounds); and by where they get their carbon: heterotrophic (from organic sources) or autotrophic (from carbon dioxide); they can also be classifed by whether or not they stain, based on the structure of their cell walls with crystal violet dye: gram-negative or gram-positive.

Unicellular, prokaryotic organisms that reproduce by cell division and usually have cell walls; can be shaped like spheres, rods or spirals and can be found in virtually any environment.

Bacteria are microorganisms that have circular double-stranded DNA and (except for mycoplasmas) cell walls. Most bacteria live extracellularly. Some bacteria (eg, Salmonella typhi; Neisseria gonorrhoeae; Legionella, Mycobacteria, Rickettsia, Chlamydia, and Chlamydophila species) preferentially reside and replicate intracellularly. Some...

Bacteria are microorganisms that have circular double-stranded DNA and (except for mycoplasmas) cell walls. Most bacteria live extracellularly. Some bacteria (eg, Salmonella typhi; Neisseria gonorrhoeae; Legionella, Mycobacteria, Rickettsia, Chlamydia, and Chlamydophila species) preferentially reside and replicate intracellularly. Some...