Which test in the IMViC series assesses the ability of organisms to ferment glucose?

The Methyl red test is designed to assess an organism's ability to perform mixed acid fermentation of glucose. This fermentation pathway results in the production of stable acids that lower the pH of the medium, which is subsequently detected by the pH indicator methyl red. If the medium turns red upon the addition of methyl red, it indicates that the organism has produced strong acids during the fermentation process, confirming glucose fermentation.

The other tests in the IMViC series focus on different metabolic pathways. For instance, the Voges-Proskauer test detects the production of acetoin from glucose fermentation, which would not indicate direct glucose fermentation. The Citrate test evaluates the organism's ability to use citrate as a sole carbon source, and the Indole test measures the hydrolysis of tryptophan to indole, neither of which directly assesses glucose fermentation.