Escherichia coli (Migula 1895) Castellani and Chalmers 1919 Escherichia coli (commonly E. coli; pronounced /ˌɛʃɪˈrɪkiə ˈkoʊlaɪ/, /iː ~/, and named for its discoverer), is a Gram negative bacterium that is commonly found in the lower intestine of warm-blooded organisms (endotherms). Most E. coli strains are harmless, but some, such as serotype O157:H7, can cause serious food poisoning in humans, and are occasionally responsible for costly product recalls. The harmless strains are part of the normal flora of the gut, and can benefit their hosts by producing vitamin K2, or by preventing the establishment of pathogenic bacteria within the intestine.