Voges – Proskauer Test

Voges – Proskauer or VP test is used as one of the key test in identification of bacterial culture. This is one of the reference test, on the basis of its result we can group bacterial colonies and can be used in identification.

VP test is used to detect presence of acetoin in a bacterial broth culture. If the bacterial culture using sugar and making acetoin then it can be detected by the VP test and can be said that bacterial culture is of kind which is utilizing sugar and making acetoin, because VP test is positive for a given bacteria.

The VP test is performed by adding alpha-naphthalene and potassium hydroxide to the Voges – Proskauer broth, which is basically a glucose-phosphate broth. A cherry red color on the growth of microorganisms which has been inoculated in it, represent a positive result, while a yellow-brown color indicates a negative result.

Procedure

Over night culture of bacterial colony on VP broth is required for the test. First add, alpha-naphthol and then, add potassium hydroxide in the VP broth in which test bacteria is inoculated, after taking a test sample in a test tube.

Reversal in order of the reagent I added to the test tube of VP broth with bacterial culture, may result in false negative or weak – positive reaction.