In diagnosing Vibrio infections, what is the typical oxidase reaction and Gram-stain appearance?

• A. Oxidase-negative cocci
• B. Oxidase-positive curved Gram-negative rods
• C. Gram-positive rods, catalase-positive
• D. Acid-fast bacilli

Answer: (B)

The main idea is recognizing Vibrio by its oxidase reaction and Gram-stain appearance. Vibrio species are Gram-negative bacteria that appear as curved (comma-shaped) rods under the microscope. They are oxidase positive, meaning they produce the enzyme cytochrome c oxidase and give a positive reaction in the oxidase test. This combination—Gram-negative, curved morphology, and oxidase positivity—is characteristic of Vibrio and helps distinguish them from other GI pathogens. For contrast, oxidase-negative cocci would not fit the Vibrio profile, Gram-positive rods point to other organisms, and acid-fast bacilli are a different staining category altogether.