AXIO Proficiency Testing | Coliform Test Results in LGC Proficiency Testing Schemes
Definition of a coliform
Coliforms are Gram-negative rods that are non-spore-forming, oxidase-negative, facultative anaerobes. Coliforms are not defined by their taxonomy but generally include species from the four genera Escherichia , Citrobacter , Klebsiella and Enterobacter. These genera, along with Proteus , Salmonella , Serratia , Shigella and Yersinia , form the Enterobacteriaceae family. According to ISO 4832:2006 (1) coliforms are bacteria which form characteristic colonies in crystal violet neutral red bile lactose agar (VRBL), and which in confirmation tests cause fermentation of lactose with the production of gas (under the specified test conditions). ISO 9308-1 (2) defines coliforms as lactose positive bacteria which are oxidase-negative. Lactose positive bacteria are bacteria capable of forming colonies aerobically on a selective and differential lactose culture medium with the production of acid. Different national regulations may also have their own definition for coliforms, for example, the United States Food and Drug Administration (FDA) defines them as Gram - negative rods which produce acid and gas as a result of lactose fermentation. ISO 4832:2006 and ISO 4831:2006 state that the definition of coliforms for each specific method “is not necessarily identical to the corresponding definitions given in other published texts.” This is true outside of ISO standards for other specific national coliform procedures.
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