E. coli gives pink colour with –
**Core Concept**
E. coli is a gram-negative bacterium that can be identified using various biochemical tests. One such test is the methyl red test, which detects the ability of an organism to produce acid from glucose fermentation. This test is useful in identifying E. coli and differentiating it from other gram-negative bacteria.
**Why the Correct Answer is Right**
The methyl red test is based on the ability of E. coli to produce acid from glucose fermentation. When E. coli ferments glucose, it produces acid, which lowers the pH of the medium. The methyl red indicator in the medium changes color from red to pink in the presence of acid. This color change is a positive result, indicating that the organism is E. coli. The acid production is due to the action of the enzyme pyruvate dehydrogenase, which converts pyruvate to acetyl-CoA, resulting in the production of acid.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify the biochemical test used to identify E. coli. While other tests may be used to identify E. coli, the methyl red test is a specific test that detects acid production from glucose fermentation.
* **Option B:** This option is incorrect because it does not mention the biochemical test used to identify E. coli. Additionally, the use of lactose in this context is not relevant to the identification of E. coli.
* **Option C:** This option is incorrect because it does not specify the biochemical test used to identify E. coli. While other tests may be used to identify E. coli, the methyl red test is a specific test that detects acid production from glucose fermentation.
**Clinical Pearl / High-Yield Fact**
The methyl red test is a useful tool in identifying E. coli and differentiating it from other gram-negative bacteria. It is essential to remember that the test detects acid production from glucose fermentation, which is a characteristic feature of E. coli.
**Correct Answer:** B. Methyl red test.