Oxidase Test

Categorized: Microbiological Techniques

This tests for the presence of electron transport system in Pseudomonas species.


  • Filter paper
  • 1% N,N,N’N’ tetramethyl-p-phenylenediamine


From Colonies:

  1. Pre-wet filter paper with oxidase reagent (N,N,N’,N’-p-phenylenediamine) and allow to dry.
  2. Pick a bacterial colony with a sterile toothpick.
  3. Gently scratch the colony onto the filter paper. A blue color is produced by Pseudomonas species.

From Liquid Culture:

  1. Spot the filter paper with 10 to 20 µl of culture.
  2. Add 10 µl of freshly made oxidase reagent and look for production of a blue color.

NOTE: If the filter paper is pre-wetted with oxidase reagent, false positive can occur.