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

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.


  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
Microdase Test (Modified Oxidase Test). Right: Negative Left: Positive
Microdase Test (Modified Oxidase Test).
Right: Negative
Left: Positive


  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


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

4 thoughts on “Modified Oxidase Test (Microdase): Principle, Procedure and Uses

    1. Tankeshwar Acharya

      - Edit


      Ira Ji,
      Thank you so much for your question. We have directly purchased Microdase from the commercial suppliers. As we have not tried that particular method, its too early for me to tell you exact answer. But if you wish, you can first check it with standard isolate and compare with standard disc and see the variation on results, if any.

    1. Tankeshwar Acharya

      - Edit


      Dear Tpegey
      Thank you for your query. Is there any “tentative test for determination of bacterial motility?”. The motility of bacterial isolate can be determined either by Microscopy or via culture on semisolid media. Please find out details here

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