E.coli bacteria. Coloured scanning electron micrograph of the rod-shaped, Gram-negative bacteria Escherichia coli, commonly known as E. coli. These bacteria are normal inhabitants of the human intestine (also animal intestines) 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 'traveller's diarrhoea'; and of 80% of all urinary tract infections. E.coli 0157:H7 can cause additional complications in children and the elderly; renal failure, anaemia, and dehydration especially for children and spontaneous bleeding, organ failure, and mental changes in the elderly. Some of these patients develop permanent disabilities or die. Magnification: x4000 when printed at 10 centimetres wide