Voges-Proskauer (VP) test

General

The VP test shows if the bacterium has butanediol fermentation and can split glucose to acetoin via pyruvat and further to 2,3-butanediol according to:

2 pyruvate + NADH --> 2CO₂ + 2,3-butanediol.

If KOH (potassium hydroxide) is added, acetoin will be converted to diacetyl (= 2,3-butanedione), which reacts with alpha-naphtol and forms a pink complex.

Method

1. Suspend one colony from the pure culture, which is to be investigated, in VP/MR medium.
   
2. Incubate at 30-37ºC during 24-48 h.
3. Add 0.2 ml of 40% KOH and then 0.6 ml of alpha-naphtol solution.
   

• Positive test result: colour change to pink.
• Negative test result: no colour change.
  

Voges-Proskauer test, where the tube to the right shows a positive test resultt. (Image: SLU/SVA.)

Use

Klebsiella spp. and Enterobacter spp. has the capacity to perform butanediole fermentation in contrast to Escherichia coli, Salmonella spp. and Shigella spp.