E. coli O157 bacteria. Coloured scanning electron micrograph (SEM) of Escherichia coli O157 strain H7 bacteria, a cause of food-borne illness. These Gram-negative intestinal bacteria (enterobacteria) were the cause of a food- poisoning outbreak in Scotland in 1996, in which several people died. The bacteria can cause bloody diarrhoea and kidney failure, particularly in the elderly and the very young. They are found in the intestines of some cattle, and can spread to humans in contaminated beef and milk. Transmission can be prevented by thoroughly cooking meat and pasteurising milk. Magnification: x10,000 at 35mm size.