Principle
- MR VP broth contains buffered peptone as a carbon and nitrogen source for general growth requirements. Dextrose is a fermentable carbohydrate. Dipotassium phosphate is a buffering agent.
- Some Enterobacteriaceae convert glucose to pyruvate by the Embden-Meyerhof pathway. While other bacteria metabolize pyruvate by the mixed acid pathway and produce acidic end products, such as lactic, acetic, and formic acids.
- The acid so produced decreases the pH to 4.5 or below, which is indicated by a change in the color of methyl red from yellow to red.
- The glucose metabolizing and stabile acid-producing bacteria are detected by the methyl red test (MR test), If the bacteria have the ability to utilize glucose with the production of a stable acid, the color of the methyl red changes from yellow to red. While the other bacteria metabolize pyruvate by the butylene glycol pathway and produce neutral end products), one of which is acetoin (acetylmethylcarbinol).
- If acetyl methyl carbinol is produced, react ∝- naphthol, strong alkali (40% KOH), and atmospheric oxygen, converted to diacetyl. The diacetyl and quinidine-containing compounds found in the peptones of the medium condense to form a pinkish-red polymer.
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