MR-VP Broth (Glucose Phosphate Broth)

Principle And Interpretation

Ready prepared MR-VP broth can be used for studying biochemical tests viz. MR and VP tests to differentiate amongst coli-aerogenes group. This medium contains buffered peptone water, which supports growth of organisms. Dextrose serves as immediate carbon source. On growing the pure culture in the test medium after 18-24 hours the cultures are tested for MR and VP tests. MR test is performed by adding Methyl Red indicator (1007). Methyl red is a pH indicator, which determines the pH when an organism utilizes glucose. On addition of one drop of methyl red indicator (1007) at the end of the period of incubation, if the colour changes to distinct red it indicates positive test. Whereas if the reagent turns yellow or yellowish orange, it indicates negative test. VP test detects ability of the organism to produce a neutral end product acetyl methyl carbinol (acetoin) from glucose utilization. This test is done by adding 1-2 drops of Barritt Reagent A (R029) and 1-2 drops of Barritt Reagent B (R030). A positive test is indicated by pinkish red colour within 2-5 minutes. No change in colour indicates negative test.