Escherichia coli is generally regarded as part of the normal flora of the human intestinal tract and that of many animals. Serotypes of E. coli which have been implicated in human diarrhoeal diseases or food poisoning outbreaks and have been designated enteropathogenic E. coli (EEC). They grow over a wide range of temperatures, 20-40ºC with a minimum growth temperature at 10ºC and an optimum at 37ºC. Heating at 65ºC for 15-20 minutes is lethal. The pH range for growth is 4.2-8.50, with an optimum in the range of pH 7.2-7.5. E. coli will grow in the presence of 5.0% salt at 37ºC but 10% is inhibitory.