Modified oxidase test is one of the most recommended method for Gram-positive catalase positive cocci. This test is considered as one of the rapid tests, which helps us to differentiate the species of negative Staphylococci’s from the positive strains of Micrococcus by detecting the oxidation of the enzymes present in the medium. To perform this test filter paper disks are being impregnated along with the tetramethyl-p-phenylenediamine dihydrochloride, which is one of the oxidase reagents, added with the dimethyl sulfoxide are used.
However, in the presence of an atmospheric oxygen around the medium, oxidase enzyme that is being present in the medium along with the oxidase reagent and the cytochrome C results in formation of a colored compound, which is referred as indophenol.
Microdase Test Objective
The main aim of the test is to differentiate the gram-positive catalase positive cocci, micrococci from the staphylococci.
Microdase Test Principle
Microdase test is also known as modified oxidase test. This test is considered as one of the rapid tests that helps us to differentiate the species of streptococcus from the micrococcus which are the gram-positive cocci that possess the catalyze enzyme. This differentiation is usually based on process of detecting the enzyme oxidase. For this process of selecting this enzyme a filter paper along with the circular disks are impregnated with a tetramethyl-p-phenylenediamine dihydrochloride which is known as oxidase reagent in the dimethyl sulfoxide DMSO are used.
This modified oxidase reagent is prepared using a1% of tetramethyl-p-phenylenediamine in a certified grade dimethyl sulfoxide. Where as DMSO helps in improving the permeability of the cells to the reagent/ In presence of the atmospheric oxygen, the enzyme oxidase reacts with the oxidase reagent and the cytochrome C which results in the formation of a colored compound. Indophenol is used as an indicator which gives a blue or purple colored formation of a compound on the disc after it is introduced into the disc that contains a bacterial colony.
Microdase Test Reagents
Here, the filter paper disks are impregnated along with the oxidase reagent known as tetramethyl-p=phenylenediamine dihydrochloride in a DMSO (dimethyl sulfoxide).
Microdase Test Procedure
This test is usually performed on the aerobic, catalase-positive and a gram-positive coccus. Initially with the help of a forceps, disk is placed on the empty Petri disk or on a sterile glass slide.
Then a small amount of several colonies is taken from an 18 to 24-hour pure culture which is grown on a blood agar on a small area of the microdase disk, using a wooden applicator.
Then the medium is incubated at a room temperature of about 2 minutes and it is noted that whether there is any change in color. Usually, blue color is noted for positive results.
Microdase Test Results
Positive Microdase Test Results: In case of positive result, the development of blue to purple color can be observed within 2 minutes after incubation.
Negative Microdase Test Results: on the other hand, if the result is negative, Staphylococci should yield a negative result, on exception with the species like Staphylococcus sciuri, S. vitulinus or S. lentus.
Microdase Test Uses
Microdase Test is most commonly used for differentiating the species of Micrococci from the Streptococci. Here most probably Micrococci is considerably yielding a positive result, and the Streptococci yields a negative result, having few exceptions with some of the species of Streptococcus like S. sciuri, S. Vitulinus, S. lentus.
Microdase Test Limitation
Staphylococci yields a negative result for some species of the Streptococci.
Bacteria which are taken from the culture that is grown on a blood agar for 24 to 36 hours only should be used for this test because the cultures that are too young or too old often gives inaccurate results.
Modified oxidase test is usually recommended for the Gram-positive catalase positive cocci only.
Where the species of the Macrococcus and the Kocuria kristinae also often known to possess a cytochrome.
Microdase is not designed for the routine testing of the oxidase activity of the activity instead it is used for testing only the species of Staphylococcus and the Micro coccus.
Microdase Test Citations