Escherichia coli serotype O157:H7 is a Shiga toxin-producing pathogen. This serotype has been reported as an etiological agent in sporadic and outbreak cases of haemorrhagic colitis. It is also associated with haemolytic uraemic syndrome. Certain E. coli serotypes other than O157:H7 also produce Shiga toxin. However, the diarrhoea caused by these other serotypes is not usually bloody. Additionally, E. coli serotype O157:H7 does not ferment sorbitol, whereas most other serotypes do. Therefore, if Sorbitol MacConkey Agar is used as a primary screen, the colonies of E. coli serotype O157:H7 appear colourless (non-sorbitol-fermenting colonies [NSFC]) while colonies of the other serotypes appear characteristically pink (sorbitol-fermenting colonies [SFC]).