Explain the Voges Proskauer (VP) Test?

As it has been discussed in previous exercise, second group of enteric bacteria produces acid during early incubation which rapidly converted to non-acidic components, i.e., 2, 3 butanediol and acetoin (acetylmethylcarbinol). These components can be detected by using Barritt's reagent, which is a mixture of alcoholic alpha-naphthol and 40% potassium hydroxide solution.

Acetylmethylcarbinol is oxidized to a diacetyl compound in presence of the alpha-naphthol catalyst and a guanidine group present in the peptone of MR-VP medium. This results in formation of a pink complex imparting rose red colouration to a medium after 15 minutes. Development of rose red colour indicates positive VP reaction while absence of it is a negative result.