Coliform bacteria are Gram-negative, rod-shaped bacteria that are aerobic or facultatively anaerobic and ferment lactose with the production of acid and gas within 48 hours at about 35 °C.
Explanation
The term “coliform” is a functional grouping rather than a taxonomic one. Members of the coliform group possess the enzyme β-galactosidase, which enables them to metabolize lactose. They are oxidase-negative and non-spore-forming. Coliforms occur naturally in soil, surface water, vegetation, and the intestines of warm-blooded animals. In public health, they are divided into total coliforms, which include genera such as Enterobacter, Klebsiella, and Citrobacter, and fecal coliforms, which grow at elevated temperatures and are more closely associated with fecal material. Escherichia coli is the principal fecal coliform species and is widely used as an indicator of fecal contamination. Most coliforms are harmless, yet their presence in drinking water suggests that other pathogenic organisms may be present.
Importance and testing
Coliform counts are used to assess the sanitary quality of water and food. Standard methods include multiple tube fermentation and membrane filtration tests, in which samples are incubated on selective media and the formation of acid and gas or metallic sheen colonies indicates coliforms. Many regulatory agencies set limits on coliform levels in potable water supplies. High counts prompt investigation and corrective actions such as disinfecting wells, repairing sewage systems or improving hygiene practices. Understanding the ecology of coliforms helps differentiate between environmental sources and fecal pollution.
Monitoring coliform bacteria is an essential part of water quality management and serves as a practical proxy for detecting possible contamination by enteric pathogens.
Related Terms: fecal indicator bacteria, Escherichia coli, water quality, lactose fermentation, Gram-negative