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BACKGROUND
Voges-Proskauer’s test is named after two microbiologists after they observed a red colour reaction that was produced after a particular media was treated with potassium hydroxide. Later it was discovered that red colour is due to acetyl-methyl carbinol production. Then in the year 1936, the test was made more sensitive when Baritt added alpha-naphthol to the respective medium before addition of potassium hydroxide.
Principle: The purpose of these test is to know whether the organism is producing acetyl-methyl carbinol or not from glucose fermentation. If yes, it is converted to diacetyl in the presence of alpha-naphthol and potassium hydroxide.
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REQUIREMENTS
Sample: Bacterial sample.
Media: MR-VP Broth
Reagents: Baritt reagent A – 5G Alpha naphthol in 100 ml absolute ethyl alcohol.
Baritt reagent B – Potassium Hydroxide 400 gm in 1000 ml Distilled water.
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PROCEDURE
Take the pure culture of the test organism and inoculate it in MR-VP broth. Then keep it for incubation for about 24 hours at a temperature 350C. After bringing out the inoculated broth from incubator, take some clean test tubes and to it add 1 ml of broth.1 Then to it add 0.6 ml of 5% alpha naphthol, then 0.2 ml of 40% KOH. Then shake the test tube well and then allow the tube to remain stagnant for about 10-15 min. If after 15 min red colour appears, it indicates the presence of diacetyl and if no colour change then negative test.2
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CONCLUSION
Results of VP test along with other biochemical test can be easily used for differentiation and identification of certain bacteria.
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REFERENCES
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Harley JP. Laboratory exercises in microbiology, 6th ed. McGraw Hill, New York, NY; 2005.
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McFadden JF. Biochemical tests for identification of medical bacteria, 3rd ed. Lippincott Williams & Wilkins, Philadelphia, PA; 2000.
