Voges–Proskauer 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
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which expl ...
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.
The test depends on the digestion of
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, usi ...
to
acetylmethylcarbinol
Acetoin, also known as 3-hydroxybutanone or acetyl methyl carbinol, is an organic compound with the formula CH3CH(OH)C(O)CH3. It is a colorless liquid with a pleasant, buttery odor. It is chiral. The form produced by bacteria is (''R'')-acetoin. ...
. 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
The IMViC tests are a group of individual tests used in microbiology lab testing to identify an organism in the coliform group. A coliform is a gram negative, aerobic, or facultative anaerobic rod, which produces gas from lactose within 48 hour ...
series, which tests for evidence of an enteric bacterium. The other three tests include: the
indole test the
methyl red test and the
citrate test [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
''Klebsiella'' is a genus of Gram-negative, oxidase-negative, rod-shaped bacteria with a prominent polysaccharide-based capsule.
''Klebsiella'' species are found everywhere in nature. This is thought to be due to distinct sublineages developin ...
'', ''
Serratia marcescens'', ''
Hafnia alvei
''Hafnia'' is a genus of Gram-negative, facultatively anaerobic, rod-shaped bacteria in the family Hafniaceae.
''H. alvei'' is a commensal of the human gastrointestinal tract and not normally pathogenic, but may cause disease in immunocompr ...
'',
''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 furnissii'' is a Gram-negative, rod-shaped bacterium. Its type strain is ATCC 35016 (= CDC B3215). ''V. furnissii'' is aerogenic (gas-producing), and uses L-rhamnose, L-arginine, L-arabinose, maltose, and D-mannitol, but not L-lysine, L- ...
'', ''
Vibrio fluvialis'', ''
Vibrio vulnificus'', and ''
Vibrio parahaemolyticus''.
History
The reaction was developed by Daniel Wilhelm Otto Voges and
Bernhard Proskauer, German
bacteriologists in 1898 at the
Institute for Infectious Diseases.
References
External links
Voges–Proskauer reactionat
Merriam–Webster Online
Voges–Proskauer (VP) Test- Principle, Reagents, Procedure and Result
{{Clinical microbiology techniques
Biochemistry detection reactions
Microbiology techniques
Bacteriology