Acinetobacter baumannii is characteristically

• A. Motile
• B. Oxidase positive
• C. Sensitive to penicillin
• D. Able to grow on MacConkey agar

Answer: (D)

Acinetobacter baumannii is a Gram-negative, non-motile, oxidase-negative, non-fermenting bacillus. MacConkey agar is designed to grow Gram-negative bacteria and to distinguish lactose fermenters from non-fermenters. This organism can grow on MacConkey because it is not fastidious, but it does not ferment lactose, so its colonies appear colorless (non-lactose fermenters) on this medium. That combination—growth on MacConkey with non-lactose fermentation—is characteristic and helps differentiate it from other bacteria.

The other statements don’t fit as well: it is not motile, so the trait of being motile is incorrect; it is oxidase negative, not oxidase positive; and penicillin sensitivity isn’t typical for Acinetobacter, which are generally resistant to penicillins due to beta-lactamase production.