Methyl Red (MR) Test- Principle, Procedure and Results Interpretation
AIM This test is used to determine the ability of an organism to produce and maintain stable acid end products from glucose fermentation. This test is helpful in differentiating members of Enterobacteriace. Principle Methyl red is a pH indicator, with a range between 6.0 (yellow) and (red). The pH at which methyl red detects acid is considerably lower than the pH for other indicators used in bacteriologic culture media. Thus, to produce a color change, the test organism must produce large quantities of acid from the carbohydrate substrate being used. The methyl red test is a quantitative test for acid production, requiring positive organisms to produce strong acids (lactic, acetic, formic) from glucose through the mixed acid fermentation pathway. Because many species of the Enterobacteriaceae may produce sufficient quantities of strong acids that can be detected by methyl red indicator during the initial phases of incubation, only organisms that can maintain this low pH afte...