MacConkey HiCynth™ Agar w/o CV and NaCl

Principle And Interpretation

MacConkey Agar is the earliest selective and differential medium for cultivation of enteric microorganisms from a variety of clinical specimens (1, 2). Subsequently MacConkey Agar and Broth have been recommended for use in microbiological examination of foodstuffs (3) and for direct plating / inoculation of water samples for coliform counts (4). These media are also accepted by the Standard Methods for the Examination of Milk and Dairy Products (5) and pharmaceutical preparations (6). MacConkey HiCynth™ Agar w/o CV, NaCl, and Sodium Taurocholate is prepared by completely replacing animal or vegetable peptones with chemically defined peptones to avoid BSE/TSE risks associated with animal peptones.

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. 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. Lactose non-fermenting strains, such as Shigella and Salmonella are colourless and transparent and typically do not alter appearance of the medium. Yersinia enterocolitica may appear as small, non-lactose fermenting colonies after incubation at room temperature.

The medium contains HiCynth™ Peptone No.3 which provides nitrogeneous and carbonaceous compounds, long chain amino acids, vitamins and other essential nutrients. The selective action of this medium is attributed to synthetic detergent, which are inhibitory to most species of gram-positive bacteria. It is a modification of the original formulation with the exclusion of crystal violet like the regular MacConkey Agar.