Chapter 5, Problem 24E.4RQ

Summary Introduction

To explain: The fact that the Escherichia coli gives positive result, whereas Enterobacter aerogenes gives a negative result in the methyl-red test even though both produce acid and gas as end products in carbohydrate fermentation test.

Introduction: The methyl-red test is used to detect whether the organism produces an acidic end product or not. Methyl red is the indicator used. The major substrate used by the enteric organisms is glucose. However, the end products will vary based on the enzymatic pathway of the organism. Even though glucose is fermented by all the organisms with organic acid production, this test mainly separates E. coli and E. aerogenes.