Nitrate reductase test

The nitrate reductase test is a test to differentiate between bacteria based on their ability or inability to reduce nitrate (NO₃) to nitrite (NO₂) using anaerobic respiration.

Procedure:

1. Inoculate nitrate broth with an isolate and incubate for 48 hours.
2. Add 10-15 drops each of sulfanilic acid and N,N-dimethyl-1-naphthylamine. If the bacterium produces nitrate reductase, the broth will turn a deep red within 5 minutes at this step.
3. If no color change is observed, then the result is inconclusive. Add a small amount of zinc to the broth. If the solution remains colorless, then both nitrate and nitrite reductase are present. If the solution turns red, nitrate reductase is not present.