Common Biochemical Tests in Microbiology: Methyl Red Test

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BACKGROUND

Methyl-Red Test is one of the important biochemical test performed on bacterial species for studying about the ability of an organism to perform mixed acid fermentation from given glucose. It is a part of IMViC test.

Principle: Some bacteria carry out mixed acid fermentation of glucose in MR-VP medium. Mixed acid fermentation gives out products like acid mixtures mostly lactate, acetate, succinate and formate along with formate, ethanol and H₂ and CO₂.These products makes the medium acidic. Methyl red is usually a pH indicator, which is red colour in a pH of 4.4 or even less.

So, the basic objective of this test is to perform Methyl-Red test of a bacterial sample.

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REQUIREMENTS

Sample: Unknown bacterial sample.

Chemicals: MR-VP medium

Methyl red reagent

Apparatus: Test tubes

Inoculating loop

Incubator

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PROCEDURE

In two test tubes take freshly prepare MR-VP medium. To one of the test tube inoculate the sample microorganism, with the help of an inoculating loop. The other test tube containing the broth is used as a standard. Then keep both the tubes in incubator at 37^oC for about 24-48 hours for proper growth of organism.¹ After incubation, bring both tubes and to it add about 4-5 drops of Methyl Red reagent. Now leave for some time undisturbed and observe for the colour change. In the standard test tube if there is no colour change, then there is no contamination and vice-versa. If red colour is formed then it is MR positive. If no colour change then MR negative.²

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CONCLUSION

MR test is an important biochemical test used for identifying enteric organisms.

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REFERENCES

Banat IM, Nigam P, Singh D, Marchant R. Microbial decolorization of textile-dye-containing effluents: a review. Bioresource Technology. 1996;58:217–27.
Brown D, Laboureur P. The aerobic degradability of primary aromatic amines. Chemosphere. 1983;12:405–14.