What color change indicates a positive result in the Methyl Red test?

In the Methyl Red test, a red color change indicates a positive result. This test is designed to measure the pH of a culture medium after fermentation of glucose by specific bacteria. The principle behind this test is that certain bacteria that ferment glucose produce sufficient amounts of acid, which lowers the pH of the medium. Methyl Red is a pH indicator that turns red at a pH below 4.4, which occurs when the acids produced from fermentation are present in significant quantities. Consequently, if a culture shows a red color after the addition of Methyl Red, it confirms that the organism is capable of acidifying the medium, thus indicating a positive result for the Methyl Red test.