Voges-Proskauer test

Voges–Proskauer /ˈfoʊɡəs ˈprɒskaʊ.ər/ or VP is a test used to detect acetoin in a bacterial broth culture. The test is performed by adding alpha-naphthol and potassium hydroxide to the Voges-Proskauer broth which has been inoculated with bacteria. A cherry red color indicates a positive result, while a yellow-brown color indicates a negative result.

The test depends on the digestion of glucose to acetylmethylcarbinol. If glucose is being broken down, it will react with alpha-naphthol (VP reagent #1) and potassium hydroxide (VP reagent #2) to form a red color. Alpha-naphthol and potassium hydroxide are chemicals that detect acetoin.

Procedure: First, add the alpha-naphthol; then, add the potassium hydroxide. A reversal in the order of the reagents being added may result in a weak-positive or false-negative reaction.

VP is one of the four tests of the IMViC series, which tests for evidence of an enteric bacterium. The other three tests include: the indole test [I], the methyl red test [M], and the citrate test [C].

VP positive organisms include Enterobacter, Klebsiella, Serratia marcescens, Hafnia alvei, Vibrio cholera biotype eltor, and Vibrio alginolyticus.

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