A bacterial culture tests positive for the oxidase test. Which statement best describes what this indicates about its respiration?

• A. It exclusively uses anaerobic respiration.
• B. It is oxidase-positive and uses aerobic respiration with cytochrome c oxidase.
• C. It performs fermentation only.
• D. It cannot respire.

Answer: (B)

A positive oxidase test means the bacterium has cytochrome c oxidase, an enzyme in the electron transport chain that transfers electrons to molecular oxygen. This indicates the organism uses aerobic respiration when oxygen is available, with oxygen as the final electron acceptor and reliance on the ETC involving cytochrome c oxidase. The other ideas don’t fit because exclusive anaerobic respiration or fermentation don’t depend on this enzyme and would not yield a positive oxidase result, and saying it cannot respire contradicts the presence of cytochrome c oxidase.