For determination of coliform bacteria particularly Enterobacteriaceae on the basis of their ability to ferment lactose. TM Media, a manufacturer and suppliers of chromogenic coliform agar or CCA as per iso in India.
CHROMOGENIC COLIFORM AGAR (CCA) is used for enumeration of Escherichia coli and other coliforms in water samples by membrane filter technique. This medium contains enzymatic digest of casein, yeast extract, sorbitol and sodium pyruvate as sources of carbon, nitrogen, fermentable carbohydrate and other essential growth nutrients for the growth of microorganisms. Disodium hydrogen phosphate and sodium dihydrogen phosphate are the buffering agents. Sodium chloride maintains the osmotic equilibrium in the medium. L- Tryptophan improves the indole reaction and gives improved differentiation between Escherichia coli and other coliforms. Tergitol-7 inhibits gram positive bacteria. The two chromogens used; salmon-β-D-galactoside and X- glucuronide help in differentiation of Escherichia coli and other coliforms on the basis of colony colour. The enzyme β-D-galactosidase cleaves salmon-β-D-galactoside, and gives a salmon to red colour to the coliform bacteria. E. coli have β-D galactosidase and β-D-glucuronidase enzymes to cleave both the chromogens, which give blue-violet colour to colonies. Expression of β-D-galactosidase is strengthened in the presence of IPTG. Agar is a gelling agent.