Coliform

Coliforms are a broad group of Gram-negative, non-spore-forming, rod-shaped bacteria that are typically facultatively anaerobic and lactose-fermenting. By conventional microbiology criteria, coliforms ferment lactose with the production of acid and gas within 24 to 48 hours at 32 to 37 degrees Celsius. They belong to the family Enterobacteriaceae and are commonly found in the environment as well as in the intestinal tracts of warm-blooded animals. The group includes several genera, most notably Escherichia, Klebsiella, Enterobacter, Citrobacter, and Serratia.

Coliforms are used primarily as indicator organisms to assess the sanitary quality of water, foods, and clinical samples. Their presence suggests potential fecal contamination and the possible presence of more pathogenic organisms, although coliform bacteria themselves are not necessarily pathogenic. In testing paradigms, distinctions are made among total coliforms, fecal coliforms, and Escherichia coli. Fecal coliforms are a subset that are thermotolerant and more closely associated with fecal material; E. coli is the most specific fecal indicator organism in many contexts.

Detection methods for coliforms include culture-based approaches such as the multiple-tube fermentation test and membrane filtration, often with confirmatory tests. Modern rapid methods employ enzymatic assays and integrated platforms (for example, Colilert) that detect indicators such as β-glucuronidase activity to identify E. coli and other coliforms.

Ecology and health considerations: many coliforms are environmental and nonpathogenic, but some genera can cause opportunistic infections. The presence of coliforms in drinking water or foods triggers actions to reduce contamination and protect public health.