Vibrio cholerae is described as a comma-shaped bacterium.

• A. Escherichia coli
• B. Vibrio cholerae
• C. Clostridium difficile
• D. Salmonella typhi

Answer: (B)

Shape-based clues are a quick way to group bacteria, and comma-shaped rods define the vibrios. Vibrio cholerae belongs to this genus, which is characterized by curved, comma-like (spiral) rods, typically with a single polar flagellum. That distinctive curved appearance helps distinguish it from other enteric bacteria. For example, the other options are not described as curved: Escherichia coli is a straight rod; Clostridium difficile is a straight, Gram-positive spore-forming rod; Salmonella typhi is a straight Gram-negative rod. So the comma-shaped morphology points directly to Vibrio cholerae.