MacConkey agar is selective in that it inhibits Gram-positive bacterial growth and differential in that it distinguishes ________ from other coliforms that are unable to ferment lactose.

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MacConkey agar is selective for Gram-negative bacteria and differential for lactose fermenters. Escherichia coli, a coliform bacterium, can ferment lactose, producing acid and turning the medium pink, distinguishing it from non-lactose fermenters like Salmonella and Shigella, which remain colorless. Staphylococcus aureus is Gram-positive and typically inhibited by the medium.

MacConkey Agar Is Selective in That It Inhibits Gram-Positive Bacterial