Which organism has a negative oxidase test?

Which organism has a negative oxidase test?

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

Answer: (B)

The oxidase test checks for the enzyme cytochrome c oxidase in bacteria. If the enzyme is present, the test reagent is oxidized and turns dark purple within seconds (positive result). If the enzyme is absent, there is no color change (negative result). Hafnia alvei typically lacks cytochrome c oxidase, so it gives a negative oxidase test. The other organisms listed generally have this enzyme and yield a positive result, which is why Hafnia stands out as the negative oxidase tester in this group.

The oxidase test checks for the enzyme cytochrome c oxidase in bacteria. If the enzyme is present, the test reagent is oxidized and turns dark purple within seconds (positive result). If the enzyme is absent, there is no color change (negative result).

Hafnia alvei typically lacks cytochrome c oxidase, so it gives a negative oxidase test. The other organisms listed generally have this enzyme and yield a positive result, which is why Hafnia stands out as the negative oxidase tester in this group.