5 Jan 2012



The oxidase test is used to assist in the identification of Pseudomonas, Neisseria, Vibrio, and Pastuerella species, all of which produce oxidase.

A piece of filter paper is soaked with a few drops of oxidase reagent. A colony of the test organism is then smeared on the filter paper. If the organism is oxidase producing, the phenyldiamine in the reagent will be oxidized to a deep purple color.Occasionally the test is performed by flooding the culture plate with oxidase reagent but this technique is not recommended for routine use because the reagent rapidly kills bacteria. It can be useful, however, when attempting to isolate N.Gonorrhoeae colonies from mixed cultures in the absence of selected medium.The oxidase positive colonies must be removed and subcultured within 30 seconds of flooding the plate.


1.         Oxidase reagent (freshly prepared)

This is a 10 g/l solution of tetra methyl-p-phenylenediamineihydrochloride.


1.         Place a piece of filter paper in a clean Petri dish and add 2 or 3 drops of freshly prepared oxidase reagent.
2.         Using a piece of stick or glass rod (not an oxidized wire loop), remove a colony of the test organism, and smear it on the filter paper.
3.         Look for the development of a blue-purple color within a few seconds.


Blue-purple color…………………    Positive test              (Within 10 seconds)                                                                                                   Oxidase produced.

No blue-purple color………………   Negative test             (Within 10 seconds)                                                                                                No oxidase produced

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