Methyl Red/Vogoes-Proskauer (MR-VP)
One medium used for two separate but related tests, identifying butanediol (VP) or acidic fermentation products (MR) as part of the IMViC test used in the identification of Enterobacteriaceae.
•Methyl Red (MR): detects the ability of an organism to produce acidic fermentation products. Acidic procucts produce a red color in the presence of a pH-indicator methyl red.
Yellow in the presence of methyl red indicates a neutral pH.
(A) E. aerogenes: negative
(B) E.coli: positive
•Voges-Proskauer (VP): after addition of 10 drops of Barrit’s A (contains alpha-naphthol) and Barrit’s B (contains KOH) a rose color will develop if the organism is able to convert acidic fermentation products to the neutral compound 2,3 butanediol acetylmethylcarbinol (acetoin).
(C) E. aerogenes: positive
(D) E.coli: negative (brown color)