An example of an oxidase-positive, glucose nonfermenting organism is which of the following?

• A. Aeromonas hydrophila
• B. Escherichia coli
• C. Klebsiella pneumoniae
• D. Pseudomonas aeruginosa

Answer: (D)

The key idea is pairing an oxidase reaction with a glucose fermentation pattern to identify the organism. Pseudomonas aeruginosa is oxidase-positive due to its cytochrome c oxidase enzyme, and it does not ferment glucose, meaning it won’t produce acid from glucose in fermentation tests. This combination—oxidase-positive and glucose nonfermenting—is characteristic of Pseudomonas aeruginosa, a classic nonfermenting, oxidase-positive Gram-negative rod often associated with opportunistic infections. In contrast, the other organisms listed are either oxidase-negative (like E. coli and Klebsiella) or, although oxidase-positive, do ferment glucose (like Aeromonas), so they don’t fit the described profile.