Oxidase-Test

Oxidase test is a simple and rapid biochemical method for detecting the enzyme cytochrome c oxidase in the respiratory chain of cells. Oxidase test is used for the classification of bacteria (Bunte row) and in histology. The oxidase reagent reduced cytochrome c to cytochrome c oxidase. Here, the colorless reagent is oxidized (cation Würster ) to an intensely colored radical cation.

The oxidase test is specific for cytochrome c oxidases. Quinol oxidases do not respond here.

Oxidase reagents

There are three different oxidase Reagents:

Kovacs reagent

The Kovacs reagent is a solution of 10 mg / ml of N, N, N ', N'- tetramethyl-1 ,4- phenylenediamine ( TMPD ) in 100 mM phosphate buffer ( pH 7). A bacterium is oxidase positive if within one minute after addition of the reagent an intense blue color ( Wurster blue ) of the cells ceases. With no or a later reaction, the bacterium is oxidase negative.

Gordon McLeod 's reagent

Gordon - McLeod reagent is a solution of 10 mg / ml of N, N-dimethyl -1 ,4- phenylenediamine ( DMPD ) in 100 mM phosphate buffer ( pH 7). A bacterium is oxidase positive if within one minute after addition of the reagent an intense red color ( Wurster red ) of the cells ceases. With no or a later reaction, the bacterium is oxidase negative.

NADI reagent

The NADI reagent ( according to Ehrlich ) is a mixture of equal parts by volume of 50 mM α - naphthol solution in 50 vol% ethanol and 10 mg / ml of N, N -dimethyl -1 ,4- phenylenediamine solution ( DMPD ) in 100 mM phosphate buffer ( pH 7). A bacterium is oxidase positive if it sets an intense blue color ( indophenol blue ) of the cells within a minute. With no or a later reaction, the bacterium is oxidase negative.

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