**Question:** The following are true of vibrio cholerae except (a) Produces indole and reduces nitrates (b) Synthesises neuraminidase (c) Dies rapidly at low temperature (d) Vaccine confers long immunity.

**Core Concept:** Vibrio cholerae is a gram-negative bacterium that is the causative agent of cholera, a severe diarrheal illness. It is particularly dangerous due to its ability to produce a potent toxin called cholera toxin, which leads to the characteristic watery diarrhea in cholera patients.

**Why the Correct Answer is Right:** The correct answer (D) states that vaccine confers long immunity. Vibrio cholerae has no vaccine that provides long immunity. Vaccines typically protect against the bacteria for a limited period, usually years or decades, but not lifelong immunity. In contrast, cholera patients recover and develop immunity after a bout of cholera due to the production of antibodies and adaptive immune response.

**Why Each Wrong Option is Incorrect:**

A. Produces indole and reduces nitrates: Indole production is a characteristic feature of some species of Escherichia coli and Klebsiella pneumoniae, not Vibrio cholerae. Vibrio cholerae does not produce indole.

B. Synthesises neuraminidase: Neuraminidase is an enzyme that cleaves sialic acid from glycoproteins and glycolipids, which is not associated with Vibrio cholerae. This enzyme is more commonly associated with influenza viruses like the H1N1 strain.

C. Dies rapidly at low temperature: Vibrio cholerae is a mesophile, meaning it thrives at moderate temperatures (between 20°C and 40°C). While it can survive in cold environments, the statement that it dies rapidly at low temperatures is incorrect.

**Clinical Pearl:** In clinical practice, understanding the characteristics of pathogens is essential for diagnosing and treating infections appropriately. Knowledge of the specific features of different pathogens helps in differentiating between pathogens and guiding treatment decisions. In the case of Vibrio cholerae, being aware of its characteristics (e.g., moderate temperature preference) aids in diagnosing cholera and choosing appropriate treatments.