Koliformisten

Koliformisten, or coliforms, are a broad group of Gram-negative, non-spore-forming, rod-shaped bacteria that ferment lactose with gas production within a defined time and temperature. They are commonly used as indicator organisms in water quality testing because their presence suggests possible fecal contamination and the potential for enteric pathogens.

The group includes genera such as Escherichia, Klebsiella, Enterobacter and Citrobacter. Many coliforms inhabit the intestinal tracts of warm-blooded animals and humans, but some environmental species occur in soil, vegetation and surface waters. Not all coliforms are derived from fecal sources, so their detection must be interpreted carefully and often alongside other indicators.

Coliform testing distinguishes between total coliforms and fecal (thermotolerant) coliforms. Total coliforms are detected by lactose fermentation with acid and gas production in certain media at around 35°C. Fecal coliforms, particularly Escherichia coli, are sought with methods that include an elevated incubation temperature, typically around 44.5°C, to favor thermotolerant organisms. Detection is commonly performed by membrane filtration or culture-based most probable number (MPN) methods on selective and differential media.

In practice, coliforms have been used as a rapid, general indicator of sanitary quality in drinking water, recreational waters and some foods. Regulatory standards often require either the absence of total coliforms or the absence of fecal coliforms/E. coli in a given sample, with follow-up testing if coliforms are detected. Limitations include the imperfect correlation between coliform presence and actual pathogenic organisms, so coliform tests are usually part of a broader assessment of water safety.