• Microdase test is also termed as modified oxidase test.
• It is one of the rapid tests employed for the differentiation between Staphylococcus and Micrococcus which are Gram positive cocci having catalase enzyme.
• The test is based on the detection of oxidase enzyme.
• Filter paper disks impregnated with tetramethyl-p-phenylenediamine in dimethyl sulfoxide (DMSO) is used in order to detect the oxidase enzyme.
• 1% (w/v) tetramethyl-p-phenylenediamine in certified grade dimethyl sulfoxide is the preparation for modified oxidase reagent.
• DMSO serves for the permeability of cells to the reagent along with providing solubility and stability against auto-oxidation.
• When exposed to atmospheric oxygen, the oxidase enzyme reacts with the oxidase reagent and cytochrome C to yield the coloured compound, indophenol indicated as blue or purplish blue coloration on the disc after the bacterial colony is introduced on the disc.

Requirements:

1. Media: Blood agar
2. Oxidase Disc
3. Filter paper disks impregnated with tetramethyl-p-phenylenediamine dihydrochloride in DMSO.
4. Incubator
5. Forceps
6. Petri dish
7. Glass slide
8. Fresh pure colonies of test organisms

Procedure:

1. Use forceps to place the disk in an empty petri dish or on a clean glass slide.
2. Use a wooden applicator stick and rub a small amount of various colonies of an 18- to 24-hour pure culture grown on blood agar onto a small area of the microdase disk.
   Note: Do not rehydrate the disk before use.
3. Incubate at room temperature for 2 minutes.
4. Observe for a blue colour development.

Results interpretations:

• Positive result:
  • The positive test is suggested by the development of blue to purple colour within the 2 mins.
• Negative result:
  • The negative test is indicated by no any change in color.

Limitations:

• Neither too young nor too old cultures are used as they might yield inaccurate results.
• Microdase test is recommended only for the Gram-positive, catalase positive cocci.
• Microdase is limited only for the routine testing of oxidase activity of Staphylococcus and Micrococcus.

Microdase (Modified Oxidase) test: Principle, Procedure and Results interpretation

The post Microdase (Modified Oxidase) test: Principle, Procedure and Results interpretation appeared first on Online Biology Notes.