E. coli bacteria. Coloured scanning electron micrograph (SEM) of the rod-shaped, gram- negative bacteria, Escherichia coli, commonly known as E. coli. These bacteria are normal inhabitants of the intestine of humans and other animals, and are usually harmless. Under certain conditions E. coli may increase in number and cause infection. Serotypes of E. coli are responsible for gastroenteritis in children, particularly in tropical countries. In adults it is the cause of travellers' diarrhoea" and of 80% of all urinary tract infections. It is also the organism most used in genetic studies. Magnification: x8,497 at 5x7cm size. Magnification: x21,500 at 12x17cm size."