A bacterium that lives harmlessly in the intestines of animals such as cattle, reptiles, and birds. However, in humans the bacterium, which can be transmitted through foods, can cause bloody diarrhea, and also lead to hemolytic uremic syndrome (HUS), a life threatening disease. Although other known strains of E. coli are thought to be harmless to humans, the 0157:H7 strain is particularly virulent and dangerous. It has been implicated in several major outbreaks of food borne illness in recent years.

After a 1993 outbreak in the West, caused by the consumption of undercooked hamburgers, resulted in hundreds of illnesses and several deaths, USDA began regularly testing samples of ground beef for the pathogen. USDA, as part of its new hazard analysis and critical control point (HACCP) rule, also now requires all meat and poultry slaughter plants to regularly test carcasses for generic E. coli (as opposed to the 0157:H7 strain) in order to verify that their sanitary systems are effectively controlling fecal contamination.