Which organism is non-lactose fermenting, oxidase negative, and shows oxidative metabolism (O/F test shows oxidation)?

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Multiple Choice

Which organism is non-lactose fermenting, oxidase negative, and shows oxidative metabolism (O/F test shows oxidation)?

Understanding how the O/F test and oxidase status distinguish nonfermenting Gram‑negatives is key. A non-lactose fermenter won’t acidify lactose on MacConkey, which narrows the suspects. Among oxidase-negative nonfermenters, the O/F test shows whether the organism metabolizes glucose oxidatively (in the presence of oxygen) or fermentatively. If acid appears only in the open tube, the organism is oxidatively metabolizing glucose rather than fermenting it. Acinetobacter fits this pattern: it does not ferment lactose, it is oxidase negative, and it shows oxidative metabolism on the O/F test (acid in the open tube but not in the sealed one). Campylobacter and Vibrio are oxidase positive, so they don’t match the oxidase-negative criterion. Stenotrophomonas maltophilia is also oxidase negative, but the classic triad described here aligns most closely with Acinetobacter.

Understanding how the O/F test and oxidase status distinguish nonfermenting Gram‑negatives is key. A non-lactose fermenter won’t acidify lactose on MacConkey, which narrows the suspects. Among oxidase-negative nonfermenters, the O/F test shows whether the organism metabolizes glucose oxidatively (in the presence of oxygen) or fermentatively. If acid appears only in the open tube, the organism is oxidatively metabolizing glucose rather than fermenting it.

Acinetobacter fits this pattern: it does not ferment lactose, it is oxidase negative, and it shows oxidative metabolism on the O/F test (acid in the open tube but not in the sealed one). Campylobacter and Vibrio are oxidase positive, so they don’t match the oxidase-negative criterion. Stenotrophomonas maltophilia is also oxidase negative, but the classic triad described here aligns most closely with Acinetobacter.

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