MRVP Broth

Identify and differentiate amongst coli-aerogene groups using Thermo Scientific™ Remel™ MR-VP Broth. In 1898, Voges and Proskauer reported the production of a red color after the addition of potassium hydroxide to cultures grown on an appropriate medium¹. Later Barritt made the VP test more sensitive by addition of alpha naphthol to the medium². In 1915, Clarke and Lubs first described the methyl red test in differentiating between the coli-aerogenes group of enteric bacteria³. Further MR-VP broth was developed to permit both tests to be performed using the same medium.

All members of Enterobacteriaceae are, by definition, glucose fermenters, resulting in the production of acid. MR-VP Broth is recommended for use in qualitative procedures for the performance of Methyl Red (MR) and Voges-Proskaur (VP) test as an aid in the identification of enteric gram-negative bacilli.

• Both MR and VP tests can be performed in the same medium.
• Easy-to-differentiate: MR positive organisms show a red color development and VP positive organisms produce a pink-red color development, while MR and VP negative organisms produce yellow color on the surface of the medium.
• Ready-to-use: Convenience of prepared media.

The MR test is based on the use of a pH indicator, methyl red, to determine the hydrogen ion concentration present when an organism ferments glucose⁴. This medium contains buffered peptone water, which supports growth of organisms. MR-positive organisms continue to produce acids, overcoming the phosphate buffer and resulting in a low pH and a red color development. MR-negative organisms further metabolize the initial fermentation products by decarboxylation to produce neutral acetyl methyl carbinol (acetoin), which results in a neutral pH.

The VP test is based on the detection of neutral end-product acetylmethylcarbinol derived from glucose metabolism and is used primarily to separate Escherichia coli (VP negative) from the Klebsiella-Enterobacter group (VP positive). Acetylmethylcarbinol is a precursor to 2,3-butanediol, both of which are oxidized to diacetyl which is the reactant for the pink-red color produced in the VP test⁵.

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