E. coli bacteria. Coloured transmission electron micrograph (TEM) of a group of the rod-shaped, Gram-negative bacteria Escherichia coli (or E. coli). A few bacteria here are at various stages of cell division. They are normal inhabitants of the human intestine and are usually harmless as pathogens. Under certain conditions, however, E. coli might increase in number 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 80% of all urinary tract infections. It is also used in genetic engineering. Magnification: x6,000 at 6x7cm size."