MacConkey Agar Prepared - 20 pcs.

MacConkey medium is a selective medium for the preferential growth of Gram-negative bacteria. This is achieved by the addition of bile salts and crystal violet, which can largely inhibit the growth of Gram-positive bacteria. However, MacConkey is not suitable for obtaining pure cultures of Gram-negative bacteria from mixed samples containing Gram-negative and Gram-positive bacteria. Therefore, MacConkey does not serve as a purity control - for that purpose, a CLED plate, for example, should be used.

MacConkey medium can also be used as a differential medium. The addition of neutral red serves as a pH indicator, which can, for example, show a decrease in pH during lactose utilization by a red coloration of the bacteria. With lactose-positive, red-colored bacteria, cloudy halos regularly appear, which are caused by the precipitation of bile salts as a result of the pH decrease.

For the cultural differentiation of Gram-positive and Gram-negative bacteria, the combination of CLED, MacConkey, and Columbia Blood-CNA is therefore always recommended ("Beyaert system", then additionally Sabouraud-G/C for yeast detection).

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