For isolation and differentiation of lactose fermenting and non-fermenting lactose enteric bacteria. It is recommended by BIS committee under specification IS: 5887 (Part I and II) 1976, reaffirmed 2005 MacCONKEY Agaris used forisolation and differentiation of lactose fermenting and non-fermenting lactose enteric bacteria. The medium contains Peptic digest of animal tissue which provides the nitrogeneous and other essential growth compounds. Sodium chloride maintains the osmotic balance of the cells.Gram-negative bacteria usually grow well on thismedia and are differentiated by their ability to ferment lactose. Lactose fermenting strains grow as red or pink and may be surroundedby a zone of acid precipitated bile.The medium turns pink in case of lactosefermenters andyellow in case of non-lactose-fermenters, due to neutral red when the pH of the media falls below 6.8. Lactose non-fermenting strains, such as Shigella and Salmonellaare colourless and transparent and typically donot alter appearance of the medium.Sodium taurocholate is used as a selective agent. Agar is a solidifying agent.