Modified Oxidase Test (Microdase): Procedure, Uses

Last updated on June 25th, 2021

Modified oxidase test (microdase) is recommended for Gram-positive, catalase-positive cocci, only. The microdase test is a rapid method to differentiate Staphylococcus (-ve) from Micrococcus +ve) 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 that are too young or too old may give inaccurate results. The DMSO renders the cells permeable to the reagent.

Modified oxidase test is performed in the same manner as the oxidase test, except that the reagent is 6% tetramethyl phenylenediamine hydrochloride in dimethyl sulfoxide.


  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

About Acharya Tankeshwar 474 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.


  1. I have only oxidase discs available right now. Is there a way I can use DMSO to convert them into microdase discs?

    • 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.

    • 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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