E. coli bacteria. Coloured Scanning Electron Micrograph (SEM) of a cluster of Escherichia coli bacteria, commonly known as E. coli. These are rod-shaped Gram-negative bacilli bacteria (Group Enterobacteriaceae). They normally inhabit the intestine of humans and animals, and are usually harmless. Under certain conditions E. coli may increase in numbers and cause infection. Serotypes of E. coli are responsible for gastroenteritis in children, particularly in tropical countries. In adults it causes traveller's diarrhoea" and is responsible for 80% of urinary tract infections. It is also the bacteria most used in genetic studies. Magnification: x3900 at 6x7cm size."