Question

The production of sufficient acid by fermentation of glucose leads to decrease in pH such that pH of the medium falls below 4.5. Which of the following test can detect it?
A.Indole test
B. Methyl red test
C. Citrate utilization test
D. Voges-Proskauer test

Answer 1

Answer:

Option B. Methyl red test is the correct option. Methyl red test is used to determine the type of pathway which is used to utilize glucose.

Explanation:

Glucose is fermented and several acids like lactic acid, succinic acid, acetic acid, and formic acids are produced in the mixed-acid fermentation pathway.

• The phosphate buffer is overcome by the stable production of enough acid that leads the pH to fall below 4.5.
• When the pH indicator or methyl red is added to an aliquant of the culture broth, the red color will appear, and if the pH is 6 (more basic nature) the methyl red will turn yellow, which means the mixed acid fermentation pathway is unjustified as the production of acids were less. This is how the methyl acid test is used to detect the pH.