What does a positive Methyl Red test indicate about metabolism?

What does a positive Methyl Red test indicate about metabolism?

• A. Production of stable mixed-acid end products from glucose fermentation, lowering pH
• B. Acetoin production via butanediol pathway
• C. Gas production
• D. Citrate utilization

Answer: (A)

The methyl red test is about how the organism ferments glucose and what acids are produced. A positive result means the organism makes stable mixed-acid end products from glucose fermentation, which lowers the medium’s pH enough to turn the methyl red indicator red. This red color signifies strong acid production, typical of mixed-acid fermentation pathways. If an organism uses the butanediol pathway to form acetoin and weaker acids, the pH doesn’t drop as much, so the test stays negative. Gas production can occur with fermentation but isn’t what this test measures, and citrate utilization is a different metabolic test entirely.

The methyl red test is about how the organism ferments glucose and what acids are produced. A positive result means the organism makes stable mixed-acid end products from glucose fermentation, which lowers the medium’s pH enough to turn the methyl red indicator red. This red color signifies strong acid production, typical of mixed-acid fermentation pathways. If an organism uses the butanediol pathway to form acetoin and weaker acids, the pH doesn’t drop as much, so the test stays negative. Gas production can occur with fermentation but isn’t what this test measures, and citrate utilization is a different metabolic test entirely.