A positive oxidase reaction reflects the ability of a microorganism to oxidize certain aromatic amines, such as tetramethyl-p-phenylene diamine (TPD), producing colored end products. This is due to the activity of cytochrome oxidase (a.k.a., indophenol oxidase) in the presence of atmospheric oxygen.
One use of the test is for the preliminary identification of Neisseria and Moraxella species, which are both oxidase positive gram-negative diplococci.
Procedure: Using a sterile wooden stick, remove 2-3 colonies from each culture to be tested and smear on a piece of filter paper. Add a drop of the spot test (TPD) reagent to each spot. If the organism has oxidase activity, it will turn purple within 30 seconds.
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