Group of gram-negative bacteria that grow at elevated temperatures, found in the intestinal tract and, therefore, in the feces of humans and other animals. The most common is escherichia coli or E. coli. An aid to digestion and normally harmless, these rod-shaped microorganisms, if ingested through contaminated food or water, will usually lead to bacterial or viral gastroenteritis, Hepatitis A, typhoid fever, and other associated problems.