Escherichia coli

the principal species of the genus, a common facultative organism of the intestines of many different animals. The organisms are characteristically positive to indole and methyl red and negative to the Voges-Proskauer and citrate tests; serovars are based on the distribution of heat-stable O antigens, envelope K antigens of varying heat stability, and flagellar H antigens that are heat labile. Most are nonpathogenic, but pathogenic strains producing fevers and diarrhea are common (see colibacillosis). The fever-causing strains are found in urinary tract infections, abscesses, conjunctivitis, and occasionally septicemic conditions such as Winckel disease. The enteropathogenic strains (EPEC) produce intestinal disease and diarrhea, especially in hospitalized infants and other baby animals. The enterotoxigenic strains (ETEC) cause diarrhea in piglets and calves and a choleralike disease in human infants and adults. Enteroinvasive serogroups (EIEC) related to Shigella invade the epithelial cells of the human colon, causing dysentery, sometimes associated with food poisoning. These often become the predominant bacteria in the flora of the mouth and throat during antibiotic therapy. Shiga toxin–producing groups (STEC, formerly called enterohemorrhagic, or EHEC) cause acute bloody diarrhea and hemolytic-uremic syndrome. A preparation of asparaginase derived from type EC-2 is used as an antineoplastic. Enteroadherent organisms (EAEC) are subdivided into enteroaggregative groups (EAggEC) (which adhere to the enteric mucosa to form colonies and can cause diarrhea in children), and diffusely adherent (DAEC) groups.