Index >> Water Pollution Microbiology >>Coliforms

Coliforms - The term coliforms refers to Gram - negative, non  sporing rod shaped bacteria, capable of aerobic and facultatively anaerobic growth in the presence of bile salts or other surface active agents with similar growth - inhibiting properties, which are able to ferment lactose with the production of acid and gas within 48 hours at 37°C. They are oxidase negative.
The definition includes the genera Escherichia, Citrobacter; Enterobacter and Klebsiella.Coliform group is sometimes referred to as total coliforms to differentiate them from faecal coliforms.

All faecal coliforms in a water body may be accepted as being of faecal origin, whereas an unknown portion of the total coliform bacteria may be of other origins (White, 1978.). Determination of faecal coli forms provides a superior indicator of fecal pollution. Faecal coliforms are not abundant in soil due to their rapid die off in that environment. The differential faecal coliform test allows the enumeration of coliform bacteria originating from faecal sources while suppressing those of soil origin.
Thus, faecal coliform counts are very useful in the case of surface waters where numerous differing sources contribute to the total coliform count. The ratio of faecal coliforms to total coliforms varies in different environments. The ratio is about 1 :70 in saline waters whereas 1: 10 fresh waters.