D. PHILLIPS / SCIENCE PHOTO LIBRARY D. PHILLIPS / SCIENCE PHOTO LIBRARY
Intestinal bacteria. Coloured Scanning Electron Micrograph (SEM) of a variety of bacteria from the human intestine. Many types of bacteria populate the human digestive system, especially the large intestine where they account for nearly half the mass of faeces. In the small intestine bacteria help to digest food and prevent harmful disease- causing bacteria from proliferating. Rod-shaped bacteria like these blue cells are called bacilli. Ball-shaped bacteria are called cocci. One of the commonest types of bacillus in the human gut is Escherichia coli. Although usually harmless, some strains of E. coli cause "traveller's diarrhoea" on first contact. Magnification unknown.
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