Question

Methyl Red Methyl Red ve MR/V/P Questions For MR Test what does red mean? Which bacteria is positive for MR? For VP, which acid are we detecting? B A Can a bacteria be positive for both MR and VP?

Answer 1

1. MR test is the Methyl red test usually done for identification of certain members of Enterobacteriaceae. Here methyl red is used as indicator. Bacteria when grown in glucose containing medium they produce acids by the fermentation of glucose. The acidity of medium is tested by methyl red test. Methyl red indicator is prepared by mixing methyl red dye with alcohol.

When fresh bacterial suspension is taken and few drops of Methyl red indicator is dropped in suspension and suspension turns red immediately because the pH of suspension is 4.4 or less. Red indicates positive MR test.

2. Escherichia coli is positive for MR because it's suspension produces red colour with methyl red indicator.

3. The principle compound which produces from glucose fermentation is pyruvic acid which further through different metabolic process produces acetyl methyl carbinol and in adding with alpha napthol positive test it gives red colour (positive test)

4. A bacteria can be positive in both MR and VP test. some species like Serratia liquifaciens, Klebsiella planticola and Proteus myxofaciens exhibit both MR and VP test positive.