Bacterial diagnostics – oxidase test: Which of the following genera are oxidase-positive in routine bench testing using reagents such as tetramethyl-p-phenylenediamine?

Introduction / Context: The oxidase test detects cytochrome c oxidase activity and is widely used to rapidly categorize Gram-negative bacteria in clinical and environmental laboratories.

Given Data / Assumptions:

• Reagent turns dark purple when oxidized by cytochrome c oxidase.
• Classic oxidase-positive groups include Pseudomonas, Neisseria, and Vibrio.
• Testing is performed on fresh growth to avoid false results.

Concept / Approach: Presence of cytochrome c oxidase correlates with certain aerobic respiratory chains. Pseudomonas spp. (non-fermenters), Neisseria spp. (Gram-negative diplococci), and Vibrio spp. (curved rods) typically yield positive reactions within seconds when properly executed, supporting preliminary identification and guiding further tests.

Step-by-Step Solution: Recall oxidase-positive genera commonly taught. Match each option: Vibrio → positive; Neisseria → positive; Pseudomonas → positive. Because all listed are positive, choose the inclusive option.

Verification / Alternative check: Quality control strains (e.g., Pseudomonas aeruginosa as positive, Escherichia coli as negative) validate reagent performance.

Why Other Options Are Wrong: Selecting any single genus would omit other true positives; “None” contradicts well-established biochemistry.

Common Pitfalls: Using metal loops (false positives), old cultures, or reading results after the recommended time window can mislead interpretation.

Final Answer: All of these.