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Additional information on coliform nomenclature
The terms coliforms, thermotolerant coliforms and E.coli are sometimes used in literature more or less interchangeably. Microbiologists and public health authorities make distinctions between them as follows:
- 'Coliforms' refers to the broad group of bile tolerant, Gram negative bacteria that produce gas and acid from lactose at 35° to 37°C; they occur naturally in raw water, soil, organic matter and faeces.
- 'Thermotolerant coliforms' (once called faecal coliforms) are a subset of the bog group of coliforms that exhibit those same properties when grown at 44°C; they are good indicators of faecal pollution.
- 'E.coli' is the major species within the thermotolerant group of coliforms which is seperated from them by being able to carry out a particular set of other biochemical reactions. They are found in the gut of humans and animals and their presence indicates faecal pollution.
Significance of these differences
It follows, therefore, that fermentation tests in bile-lactose media on water samples that are carried out at 35° to 37°C will indicate the presence of bacteria belonging to the broad coliform group; these may or may not be of faecal origin. Positive fermentation tests conducted at 44°C (thermotolerant coliforms) indicate the presence of coliforms that may be of faecal origin. Water testing laboratories usually test for coliforms and thermotolerant coliforms.
Posted August 2006.