VOGES-PROSKAUER TEST

 

VOGES-PROSKAUER TEST

Aim

To differentiate bacteria that produces neutral product acetoin during fermentation of glucose.


Principle

VP test is a biochemical test that detects the ability of bacteria to metabolize the pyruvate into a neutral intermediate product called ‘acetylmethylcarbinol’ or acetoin . Pyruvic acid, the important  compound in the fermentative degradation of glucose, is further metabolized through various metabolic pathways, depending on the enzyme systems possessed by different bacteria. Certain bacteria produce acetoin (acetyl methyl carbinol), a neutral-reacting end product from glucose metabolism. In the presence of alkali and atmospheric oxygen,  the acetoin reacts with alpha naphthol and oxidised to form diacetyl. Diacetyl condense with quanidine-containing compounds found in the peptones of the broth to form a ruby pink colour. 


Materials required

·       24- 48 hour old bacterial culture

·       MR VP tubes (5 ml in each tube)

·       MR reagent

·       Dropper

·       Inoculating loop

·       Bunsen burner


Procedure

Ø  5 ml of MR -VP broth was inoculated with test organism.

Ø  The tubes were incubated at 37oC for 24-48 hours.

Ø  0.6 ml(6 drops) of VP reagent A was added to 24-48 hour old broth culture and mix well to aerate. 

Then add 0.2 ml(2 drops)of VP reagent B is added .

The  tubes  were gently shaken.The reaction was allowed to complete for 16-30 minutes.


Result

The culture which shows positive result yields red colour, If the broth remains orange, the test must be repeated. The yellow colour indicates negative result.

Examples

Positive:  Staphylococcus sp, Bacillus sp

Negative: Peudomonas sp, E. coli, Proteus sp

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