The generic name for the group of gram-negative, usually motile, rod-shaped BACTERIA that can ferment CARBOHYDRATE. They occur naturally in the intestines of humans and some animals. E. coli, which ferments lactose, is not normally harmful but some varieties, particularly E. coli O157, cause gastrointestinal infections which may be severe in old people. E. coli is also used in laboratory experiments for genetic and bacteriological research.
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