Escherichia coli. Scanning Electron Micrograph (SEM) of a cluster of the bacteria Escherichia coli (family: Enterobacteriaceae). They are rod-shaped bacilli, Gram-negative and motile. Each bacterium has a flagella, although not seen here. The cell wall surface is visible. E.coli bacteria inhabit the intestinal tract of humans where they play a nutritional role by synthesizing vitamins, especially vitamin K. They consume oxygen, rendering the large intestine anaerobic. In this way they are harmless and useful. Some strains of E. coli, however, are pathogenic, causing diarrhoea and urinary tract infections. Magnification: x6,000 at 35mm size.
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