This well-known microbe is a Gram negative rod-shaped bacterium commonly found in the colons of warm-blooded animals, as well as environmental sources. It serves as an important “indicator organism” for testing the safety of water and foods, as presence of this microbe indicates likely fecal contamination. The rods occur singly or in pairs and can be motile by peritrichous flagella. Growth occurs optimally at 35-37 C. E. coli is primarily an opportunistic pathogen (only causes disease in weakened hosts), but a few strains are potent pathogens. This microbe has been a valuable tool in unraveling the mysteries of genetics and molecular biology.