The Voges-Proskauer test (named after Voges and Proskauer) can help to identify certain members of the Enterobacteriaceae.
Pathway:
(1) Pyruvic acid is produced from glucose during glycolysis.
(2) Pyruvic acid is converted by the butylene glycol pathway to acetoin.
(3) Exposure to KOH converts acetoin to diacetyl.
(4) Diacetyl plus alpha-naphthol plus arginine generate a pink to red color.
Reagents:
(1) 5% alpha-naphthol in absolute ethanol
(2) 40% potassium hydroxide KOH
Testing:
(1) The isolate is grown in MR/VP broth at 35°C for 24 hours.
(2) A sample of the broth is mixed with the alpha-naphthol reagent, followed by the KOH.
(3) The mixture is shaken gently to expose it to atmospheric oxygen.
Interpretation:
• A positive result is red color developing at 15 minutes or more after the addition of the reagents.
• A positive reaction is seen with members of the Klebsiella, Enterobacter, Hafnia and Serratia group.
• Escherichia coli show a negative reaction.
Causes of a false positive reaction:
(1) reading the test an hour or more after addition of the reagents
(2) mixed culture
Causes of a false negative reaction:
(1) reading the test too soon
(2) problem with the reagents (failure to add, addition in wrong order, deterioration)
