Bacteria

Single-celled microorganisms which can exist either as independent (free-living) organisms or as parasites (dependent upon another organism for life). Examples of bacteria include: {{}}Acidophilus, a normal inhabitant of yogurt, Chlamydia, which causes an infection very similar to gonorrhea, Clostridium welchii the most common cause of the dreaded gas gangrene, E. coli, the common peaceful citizen of our colon and, upon occasion, a dangerous agent of disease, and Streptococcus, the bacterium that causes the important infection of the throat strep throat. Bacterium is the singular and bacteria the plural — one bacterium, two bacteria. The term was devised in 1847 by the German botanist Ferdinand Cohn who based it on the Greek "bakterion," a small rod or staff.

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Plural of bacterium.

- blue-green b. Cyanobacteria.

- cell wall–defective b. b. with absent or damaged cell walls; morphologically, they may become spheroplasts, round structures with little or no cell wall, or they may develop filamentous forms, with or without bulbous, extruded portions.

- coryneform b. common name for nondiphtheria corynebacterium, usually a nonpathogenic component of skin and oropharyngeal flora in humans and animals can cause opportunistic infections in the immunocompromised host.

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bacteria pl of BACTERIUM

bac·te·ria bak-'tir-ē-ə n

1) BACTERIUM not usu. used technically <caused by a \bacteria borne by certain tiny ticks (Wall Street Jour.)> <a single \bacteria-there are roughly 200 in each cough-apparently can infect a person (Cheryl Clark)>

2) pl cap a domain in the system of classification dividing all organisms into three major domains of life that includes the prokaryotes that are bacteria but not those that are archaebacteria or archaea compare eubacteria

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pl. n. (sing. bacterium)

a group of microorganisms all of which lack a distinct nuclear membrane (and hence are considered more primitive than animal and plant cells) and most of which have a cell wall of unique composition (many antibiotics act by destroying the bacterial cell wall). Most bacteria are unicellular; the cells may be spherical (coccus), rod-shaped (bacillus), spiral (Spirillum), comma-shaped (Vibrio) or corkscrew-shaped (spirochaete). Generally, they range in size between 0.5 and 5 µm. Motile species bear one or more fine hairs (flagella) arising from their surface. Many possess an outer slimy capsule, and some have the ability to produce an encysted or resting form (endospore). Bacteria reproduce asexually by simple division of cells; incomplete separation of daughter cells leads to the formation of colony consisting of different numbers and arrangements of cells. Some colonies are filamentous in shape, resembling those of fungi. Transfer of DNA from one bacterium to another takes place in the process of conjugation.

Bacteria are very widely distributed. Some live in soil, water, or air; others are parasites of humans, animals, and plants. Many parasitic bacteria do not harm their hosts; some cause diseases by producing poisons (see endotoxin, exotoxin).

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Bac·te·ria (bak-tērґe-ə) in the three-domain system of classification, one of the two large divisions into which prokaryotes are grouped, genetically distinct from the Archaea and comprising a large number of unicellular microorganisms that commonly multiply by cell division (fission) and whose cell is typically contained within a cell wall. Cf. Archaea and see bacterium.