BIOCHEM MAC CONKEY AGAR

BIOCHEM MAC CONKEY AGAR is the earliest selective and differential medium for cultivation of enteric microorganisms from a variety of clinical specimens . Subsequently MacConkey Agar and Broth have been recommended for isolation, identification and enumeration of Staphylococcus aureus and Faecal Streptococci from foodstuffs and for direct plating / inoculation of water samples for coliform counts. These media are also used by the Standard Methods for the Examination of Milk and Dairy Products and pharmaceutical preparations. 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. Gram-negative bacteria usually grow well on the medium and are differentiated by their ability to ferment lactose. Lactose fermenting strains grow as red or pink colony surrounded by a zone of acid precipitated bile. The red colour is due to production of acid from lactose, absorption of neutral red and a subsequent colour change of the dye when the pH of medium falls below 6.8. Nonlactose-fermenting strains, such as Shigella and Salmonella are colourless and transparent and do not alter appearance of the medium. Yersinia enterocolitica may appear as small, non-lactose fermenting colonies after incubation at room temperature. Bacteria such as Staphylococcus aureus and Faecal Streptococci. Causing food poisoning are also isolated on MacConkey Agar.