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colon bacillus[′kō·lən bə′sil·əs]
(Escherichia coli, Bact. coli, Bact. coli commune), a microorganism isolated by the Austrian physician T. Escherich (1885) from human feces. Based on antigenic and biochemical properties, two main species of colon bacillus are distinguished: E. coli and Citrobacter. The colon bacillus is rod-shaped with slightly rounded ends (1–3 × 0.4–0.8 microns in size); it is mobile (it has flagella). It does not form spores and is gram-negative. It is an aerobe or facultative anaerobe.
The colon bacillus usually inhabits the human intestine as one of the main constituents of the normal intestinal flora. It is always present in the intestine of most mammals, birds, fish, and insects. Its presence in water or food is indicative of fecal contamination. The method of detecting the colon bacillus is based on its ability to ferment carbohydrates (including glucose and lactose), yielding acid and carbon dioxide. Because it is a favorite object of microbiological and molecular genetic research, the colon bacillus is the organism that has been most fully studied at the molecular level. A genetic map of its chromosome has been compiled, and its patterns of mutation and principal metabolic processes have been studied.
KH. KH. PLANEL’ES