Oxidase test

Oxidase Test is a procedure used in microbiology to identify bacteria that produce the enzyme cytochrome c oxidase. This enzyme is part of the bacterial electron transport chain, where it participates in the final step of aerobic cellular respiration. The oxidase test is used as an aid for the differentiation of Pseudomonas, Neisseria, and certain other types of bacteria.

Procedure

The oxidase test is performed by adding a drop of the reagent N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) to a culture. If the bacteria oxidize the reagent, the reagent turns a dark purple color. The color change is due to the oxidation of TMPD to Wurster's blue. The test is positive if the color change occurs within 20 seconds.

Interpretation

A positive oxidase test indicates that the bacterium produces cytochrome c oxidase and can use oxygen for energy production with an electron transport chain. This is typical for aerobic bacteria and facultative anaerobes. A negative test indicates the absence of cytochrome c oxidase and suggests that the bacterium either does not use oxygen for energy production or uses it in a different way.

Limitations

The oxidase test is not definitive for identification of bacteria. It is used in conjunction with other tests and procedures. Some bacteria may give false positive or false negative results. For example, Enterobacteriaceae are typically oxidase negative, but some species may give a weak positive result.

See also

• Microbiology
• Bacterial identification
• Biochemical tests

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