Oxidase Test

Oxidase Test NOTE: This test is for Gram-negative organisms.The oxidase test determines whether a microbe can oxidize certain aromatic amines, for example, p -aminodimethylaniline, to form colored end products. This oxidation correlates with the cytochrome oxidase activity of some bacteria, including the genera Pseudomonas and Neisseria. While a positive oxidase test is important in the identification of these genera, the test is also useful in characterizing the enteric bacteria ( Enterobacteriaceae), which are oxidase-negative.

Modified Oxidase Test (Microdase Disks) NOTE: This test is for Gram-positive, catalase-positive cocci, only. You must use bacteria from a culture grown on Blood agar for 24 - 36 hours. Cultures which are too young or too old may give inaccurate results.
This test is used for differentiating Micrococcus from Staphylococcus . Micrococci should yield a positive result. Staphylococci should yield a negative result, with the exception of Staphylococcus sciuri.


Enzymatic activities are used to differentiate bacteria.
Some bacteria contain enzymes that help to speed up the rate of chemical reactions. One of these reactions is the breaking down of compounds.
Enzyme that adds oxygen during the reaction of breaking down compound is also known as oxidase.


To test for oxidase, an oxidase test is being used.
An oxidase test is a test to determine whether a bacterium contain an enzyme cytochrome oxidase. Cytochrome oxidase takes part in the electron transport chain by transferring electrons to oxygen from a donor molecule.
The oxidase reagent contains a chromogenic reducing agent, Tetramethyl-p-phenylenediamine (TMPD) or Dimethyl-p-phenylenediamine (DMPD), which is a compound that changes color when it becomes oxidized and remain colorless when reduced.


If bacterium contains cytochrome oxidase, it can use the oxygen for energy production with an electron transfer chain. The oxidase reagent will turn blue or purple within a short time. The reaction is positive.

If the bacterium does not contain cytochrome oxidase, the reagent will remain colorless. The reaction is negative.


Bacteria that show positive reactions (contain cytochrome oxidase) are oxidase positive. Examples of such bacteria are preliminary identification of Neisseria and Moraxella genera.
Bacteria that do not show positive reactions (do not contain cytochrome oxidase) are oxidase negative. Examples of such bacteria are all enteric bacteria.

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Catalase reaction




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Sources:
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Sources:
http://en.wikipedia.org/wiki/Oxidase_test
http://www.austincc.edu/microbugz/oxidase_test.php
http://web.mst.edu/~microbio/Lab_Supplement/Oxidase.html
http://www.tgw1916.net/video_pages/oxidase.html