MacCONKEY AGAR, MODIFIED

Description

MacConkey Agar is the earliest selective and differential medium for cultivation of enteric microorganisms from a variety of clinical specimens. The original medium contains protein, bile salts, sodium chloride and two dyes. The selective action of this medium is attributed to crystal violet and bile salts, which are inhibitory to most species of gram-positive bacteria. Klebsiella species are often associated with coliforms in water supply distribution systems and are present as a major component in industrial wastes of paper mill, textile and other industries. Thom developed a medium based on MacConkey Agar in which lactose is replaced by inositol with the addition of 100?g of carbenicillin per ml. Bagley and Seidler (1978) devised a similar medium with only 50?g of carbenicillin per ml. In the modified MacConkey agar medium, inositol is incorporated in place of lactose while added carbenicillin makes the medium selective for Klebsiella species. Further, this method reduces the necessity for biochemical testing of pure strains; however, preliminary verification of differentiated colonies is recommended.