Voges-Proskauer test

Voges-Proskauer test is a biochemical test used to detect the presence of acetoin in a bacterial broth culture. The test is part of the IMViC series, a group of tests used to differentiate Enterobacteriaceae and other gram-negative rods. The Voges-Proskauer test specifically identifies bacteria capable of fermenting glucose with the production of acetoin and 2,3-butanediol.

Principle

The principle behind the Voges-Proskauer test involves the detection of acetoin (acetylmethylcarbinol), a metabolic product formed during the fermentation of glucose. When the culture medium containing the bacteria is mixed with specific reagents (alpha-naphthol and potassium hydroxide), acetoin is oxidized to diacetyl, which reacts with guanidine compounds present in peptone to produce a red color. The presence of a red color after the addition of the reagents indicates a positive result, while its absence indicates a negative result.

Procedure

The Voges-Proskauer test is performed as follows:

1. A bacterial culture is grown in a broth medium that contains glucose.
2. After incubation, a portion of the broth culture is transferred to a test tube.
3. Alpha-naphthol and potassium hydroxide are added to the culture.
4. The mixture is shaken gently and allowed to stand for 15 to 60 minutes.
5. The development of a red color indicates a positive test, signifying the presence of acetoin.

Interpretation

• Positive result: Red color development indicates a positive Voges-Proskauer test, suggesting the presence of acetoin and the capability of the organism to ferment glucose with the production of acetoin and 2,3-butanediol.
• Negative result: No color change or the presence of a copper color indicates a negative result, suggesting the absence of acetoin.

Applications

The Voges-Proskauer test is used in microbiology to differentiate among members of the Enterobacteriaceae family and to identify other bacteria that produce acetoin from glucose fermentation. It is particularly useful in distinguishing between Escherichia coli (VP negative) and Enterobacter and Klebsiella species (VP positive).

Limitations

The Voges-Proskauer test has certain limitations. False positives can occur due to the presence of citrate in the medium or improper execution of the test. Additionally, the test's sensitivity and specificity can be influenced by the incubation time and the concentration of the reagents used.

Voges-Proskauer test Resources
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