E. coliPronunciation: /ˈkəʊlʌɪ/Definition of E. coli noun [mass noun] a bacterium commonly found in the intestines of humans and other animals, some strains of which can cause severe food poisoning. Escherichia coli; a motile Gram-negative bacillus E. coli in other Oxford dictionaries Definition of E. coli in the US English dictionary