:Voges–Proskauer test

{{short description|Microbiological and biochemical method for identification}}

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| footer = Two bacterial broth cultures, showing a positive result (left side) and a negative result (right side) for the VP test.

| image1 = Enterobacter cloacae Voges-Proskauer test.jpg

| caption1 = Enterobacter cloacae

| image2 = Cosenzaea myxofaciens Voges-Proskauer test.jpg

| caption2 = Proteus myxofaciens

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Voges–Proskauer {{IPAc-en|ˈ|f|oʊ|ɡ|ə|s|_|ˈ|p|r|ɒ|s|k|aʊ|.|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 is a glucose-phosphate broth that has been inoculated with bacteria. A cherry red color indicates a positive result, while a yellow-brown color indicates a negative result.MacFaddin, J. F. 1980. Biochemical Tests for Identification of Medical Bacteria, 2nd ed. Williams and Wilkins, Baltimore

The test depends on the digestion of glucose to acetylmethylcarbinol. In the presence of oxygen and strong base, the acetylmethylcarbinol is oxidized to diacetyl, which then reacts with

guanidine compounds commonly found in the peptone medium of the broth. Alpha-naphthol acts as a color enhancer, but the color change to red can occur without it.

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].Bachoon, Dave S., and Wendy A. Dustman. Microbiology Laboratory Manual. Ed. Michael Stranz. Mason, OH: Cengage Learning, 2008. Exercise 15, "Normal Flora of the Intestinal Tract" Print.

VP positive organisms include Enterobacter, Klebsiella, Serratia marcescens, Hafnia alvei, Vibrio cholerae biotype El Tor, and Vibrio alginolyticus.Bergey's Manual of Systematic Bacteriology, Vol. 1. Baltimore, Williams and Wilkins, 1984.

VP negative organisms include Citrobacter sp., Shigella, Yersinia, Edwardsiella, Salmonella, Vibrio furnissii, Vibrio fluvialis, Vibrio vulnificus, and Vibrio parahaemolyticus.