Which organism has a negative oxidase test?

Which organism has a negative oxidase test?

• A. Aeromonas
• B. Chryseobacterium
• C. Rahnella
• D. Vibrio

Answer: (C)

The oxidase test detects the presence of cytochrome c oxidase in the bacterial electron transport chain. If the enzyme is present, the reagent donates electrons and turns a dark purple within seconds. If the enzyme is absent, there is no color change and the result remains colorless. Rahnella is an oxidase-negative member of the Enterobacteriaceae, so it does not produce cytochrome c oxidase and will not change color in the test. The other listed organisms are typically oxidase-positive, meaning they do have the enzyme and yield a purple color, so they would not give a negative result.

The oxidase test detects the presence of cytochrome c oxidase in the bacterial electron transport chain. If the enzyme is present, the reagent donates electrons and turns a dark purple within seconds. If the enzyme is absent, there is no color change and the result remains colorless.

Rahnella is an oxidase-negative member of the Enterobacteriaceae, so it does not produce cytochrome c oxidase and will not change color in the test. The other listed organisms are typically oxidase-positive, meaning they do have the enzyme and yield a purple color, so they would not give a negative result.