Chromogenic Coliform Agar (CCA) – medium for enumeration of Escherichia coli and coliforms in water acc. to ISO9308:2014

E. coli-Coliforms Chromogenic Agar (CCA) is a selective medium for the detection of E.coli and other coliforms in waters according to ISO9308:2014 and replacing TTC-Tergitol 7Agar. The interaction of ingredients in the medium, such as peptone, sorbitol and pyruvate, grants a quick colony growth, including infectious coliforms and also permits the recovery of sublethal thermally injured coliforms. Tergitol-7 inhibits Gram positive bacteria and some Gram negative without affecting the coliform bacteria. Sodium chloride maintains the osmotic balance and phosphate salts act as a buffer system. The medium contains a chromogenic substrate for the detection of ß-glucuronidase activity used to differentiate Escherichia coli, as the enzyme is present in E. coli but not in other coliform. A second chromogenic substrate evidence the ß-D-galactosidase activity typical of all coliforms. The addition of tryptophan to the medium allows the performance of the Indole test for further E. coli confirmation. In the enumeration the positive colonies ß-D-galactosidase and ß-D-glucuronidase (dark blue to violet) are counted as E. coli, hence, the total coliform bacteria count is the sum of oxidase-negative colonies, ß-D-galactosidase-positive colonies (pink to red) and all colonies which dark blue to violet. Pseudomonas and Proteus grow in colorless colonies.

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