Coliform bacteria

Coliform bacteria are a commonly-used bacterial indicator of sanitary quality of foods and water. They are defined as rod-shaped Gram-negative organisms which ferment lactose with the production of acid and gas when incubated at 35 °C. Coliforms are abundant in the feces of warm-blooded animals, but can also be found in the aquatic environment, in soil and on vegetation. In most instances, coliforms themselves are not the cause of sickness, but they are easy to culture and their presence is used to indicate that other pathogenic organisms of fecal origin may be present. Fecal pathogens include bacteria, viruses, protozoa or parasites.

Typical genera include:
 * Citrobacter,
 * Enterobacter,
 * Escherichia,
 * Hafnia,
 * Klebsiella,
 * Serratia and
 * Yersinia.

Escherichia coli (E. coli), a rod-shaped member of the coliform group, can be distinguished from most other coliforms by its ability to ferment lactose at 44°C, and by its growth and colour reaction on certain types of culture media. Unlike the general coliform group, E. coli are almost exclusively of fecal origin and their presence is thus an effective confirmation of fecal contamination. Typically, E. coli are about 10% of the coliforms in human feces.