Modified Oxidase Test (Microdase): Principle, Procedure and Uses - microbeonline

Modified oxidase test (microdase) is recommended for Gram-positive, catalase-positive cocci, only. The microdase test is a rapid method to differentiate Staphylococcus from Micrococcus by detection of the enzyme oxidase. Filter paper disks impregnated with tetramethyl-p-phenylenediamine dihydrochloride (oxidase reagent) in dimethyl sulfoxide (DMSO) are used.

In the presence of atmospheric oxygen, the oxidase enzyme reacts with the oxidase reagent and cytochrome C to form the colored compound, indophenol.

Related topic: Oxidase test: Principle, Procedure, Results and Oxidase positive organisms

Bacteria from a culture grown on Blood agar for 24 – 36 hours must be used. Cultures which are too young or too old may give inaccurate results. The DMSO renders the cells premeable to the reagent.

Procedure:

1. Using sterile forceps, transfer a Microdase disk from the stock bottle to a petri dish. Return the bottle of disks to the refrigerator, promptly.
2. Using a wooden applicator stick, rub a small amount of several colonies of an 18-24 hour pure culture grown on blood agar onto the top of microdase disk.
3. Incubate at room temperate for 2 minutes

Result:

1. Positive test: A blue or purple-blue color change within 2 minutes
2. Negative test: No change in color

Quality Control:

1. Positive: Micrococcus luteus
2. Negative: Staphylococcus aureus

Uses:

Modified oxidase 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, S. lentus and S. vitulinus

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‏Source microbeonline.com