normal flora


nor·mal flor·a

(nōr'măl flōr'ă) Microorganisms that normally reside at a given site and under normal circumstances do not cause disease.

normal flora

Microorganisms including bacteria, protozoa, and fungi that are found on or in specific areas of the body. The skin and mucous membranes of the oral cavity, intestines, upper respiratory tract, and vagina have specific, permanent flora. They are harmless, even beneficial, in their usual sites, and they inhibit the growth of pathogens, but they can cause infection if they are introduced into unusual sites. If the proportions of the various microorganisms are disrupted, one species may overgrow, as does Candida when bacterial flora are diminished by antibiotics. Synonym: resident flora See: colitis, pseudomembranous; infection; microorganism

The largest concentration of bacteria in humans is in the colon, where more than 400 genera may coexist. In the colon, anaerobic bacteria outnumber aerobic bacteria 1000:1, and there may be 1011 per g of fecal material. The anaerobic gram-positive lactobacilli may be concentrated in the vagina at the 105 to 108/ml level, but 20% of women have no detectable anaerobes in the vagina. In dental plaque and gingival sulci, the bacteria may reach a concentration of 1012/ml.

See also: flora

Normal flora

The mixture of bacteria normally found at specific body sites.Mentioned in: Sputum Culture, Wound Culture