Which organism is oxidase negative?

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Prepare for the NBME Microbiology Test. Study with flashcards and multiple-choice questions. Each query comes with hints and detailed explanations. Ace your exam!

Multiple Choice

Which organism is oxidase negative?

Explanation:
The test looks for cytochrome c oxidase, an enzyme used in many aerobic bacteria to transfer electrons to oxygen. If this enzyme is present, the oxidase reagent becomes oxidized and immediately turns the sample purple, indicating a positive result. If the enzyme is absent, there’s no color change, signaling a negative result. Organisms like Pseudomonas aeruginosa, Neisseria meningitidis, and Vibrio vulnificus have cytochrome c oxidase and therefore give a positive oxidase test. Salmonella typhi, on the other hand, belongs to the Enterobacteriaceae family that typically lacks cytochrome c oxidase, so it shows an oxidase-negative result.

The test looks for cytochrome c oxidase, an enzyme used in many aerobic bacteria to transfer electrons to oxygen. If this enzyme is present, the oxidase reagent becomes oxidized and immediately turns the sample purple, indicating a positive result. If the enzyme is absent, there’s no color change, signaling a negative result.

Organisms like Pseudomonas aeruginosa, Neisseria meningitidis, and Vibrio vulnificus have cytochrome c oxidase and therefore give a positive oxidase test. Salmonella typhi, on the other hand, belongs to the Enterobacteriaceae family that typically lacks cytochrome c oxidase, so it shows an oxidase-negative result.

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