In 1898 Voges and Proskauer characterized
the fermentation of sugars by various bacterial isolates. This method was suggested for differentiation
between bacterial isolates that produced coloration and those that did not. Both the methyl red
and Voges-Proskauer tests are commonly used in conjunction with the indole and citrate
tests, to form a group of tests known as IMViC which aid in the differentiation of Enterobacteria The Voges-Proskauer test determines the capability
of some organisms to produce non acidic or neutral end products, such as acetyl methyl
carbinol, from the organic acids that result from glucose metabolism. This test differentiates
among the enteric organisms such as Escherichia coli, Enterobacter aerogenes and Klebsiella
pneumonia . The reagent used in this test is Barritt’s
reagent, consists of a mixture of alcoholic a-naphthol and 40% potassium hydroxide solution.
Detection of acetyl methyl carbinol requires this end product to be oxidized to a diacetyl
compound. This reaction will occur in the presence of the a-naphthol catalyst and a
guanidine group that is present in the peptone of the MR-VP medium. As a result, a pink complex
is formed, imparting a rose color to the medium. Petri plate containing culture
Barritt’s reagents A and B. Sterile MR-VP broth tubes
Bunsen burner Inoculating loop Arrange all the materials in LAF
Sterilize the loop vertically in the blue flame of the Bunsen burner till red hot.
Take the petri plate containing the colony. Now open the petri plate in presence of flame
and take an isolated colony using the inoculation loop.
Take a sterile MR-VP broth tube, remove the cap and flame the neck of the tube.
Inoculate the MR-VP broth with the inoculation loop containing isolated colony from the Petri
plate Again flame the neck of the tube and place
it in the test tube rack. Incubate the tube for 24 to 48 hours at 37
°C in a shaking incubator After 24 hours, take the tube out, remove
the cap and add 10 drops each of Barritt’s A and Barritt’s B reagent s respectively
Shake gently for several minutes. A red color within the first 15 to 20 minutes
is a positive result. No red color formation after 15 to 20 minutes is a negative result.