MacConkey agar is a selective and differential medium. It selects for Gram- negative bacterial organisms while differentiate between those that can and cannot ferment lactose / lactose metabolism.
The selective and differentiation properties of MacConkey agar enable the utilization for the both research an clinical applications. And the fermentation of lactose produces organic acids, particularly lactic acids, which decreased the pH of agar. Lactose fermenting species are grow in pink colonies and produce acidic byproducts.
ferment lactose -gram-negative will form off white opaque colonies. MacConkey agar only gram-negative bacteria and those bacteria will appear differently based on their lactose fermenting ability as well as the rate of fermentation.
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