methyl red test
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methyl red testA colorimetric test for differentiating Enterobacteriaceae.
An inoculum of bacteria is placed in a buffered glucose-peptone broth; the MRT is based on a change in pH, and usually results in the opposite reaction as that of the Voges-Proskauer test—therefore Enterobacter aerogenes, which is positive in the VPT, serves as a negative control in the MRT. Escherichia coli is positive (red) at 48 hours, Enterobacter aerogenes is negative.