Chromogenic Listeria Agar Base is used for selective identification and differentiation of Listeria monocytogenes. Peptone, Tryptone and Yeast extract provide nitrogen, vitamins, minerals and amino acids essential for growth. Sodium chloride maintains the osmotic balance of the medium. Agar is a solidifying agent. Sodium pyruvate is a source of energy and helps in revival of stressed organisms. Glucose serves as carbon and energy source. Magnesium glycerophosphate and disodium hydrogen phosphate serve as buffering compound. Magnesium sulphate supplies magnesium ion, required for various enzymatic reactions, including DNA replication. Lithium chloride and Chromogenic Selective Supplement (TS 205) inhibit growth of most gram positive bacteria, gram negative bacteria, yeasts and moulds. Listeria Lipase C Supplement (TS 031) facilitates the detection of phosphatidylinositol phospholipase C (PIPLC), produced by Listeria monocytogenes. This medium is helpful in specific detection of β-glucosidase activity. Listeria species hydrolyse the chromogenic substrate X-glucoside in the medium giving blue coloured colonies. Since β-glucosidase activity is specific for Listeria species. Other organisms that possess this enzyme are inhibited by the selective agents. Organisms, unable to utilize the chromogenic substrate, give white colonies. Further, the differential activity is also obtained by lipase C substrate, upon which the specific enzyme for L. monocytogenes acts and gives an opaque white halo around L. monocytogenes colonies.