Gonorrheal infection diagnosed in pharyngeal or rectal sites is most effectively detected by which culture?

• A. Blood agar
• B. Thayer-Martin culture
• C. MacConkey
• D. Chocolate agar

Answer: (B)

Isolating Neisseria gonorrhoeae from pharyngeal or rectal specimens requires a selective, enriched culture that can grow the organism while suppressing the abundant normal flora found at these sites. Thayer-Martin medium is designed for this purpose, incorporating antibiotics such as vancomycin, colistin, and nystatin to inhibit Gram-positives, many competing Gram-negatives, and fungi, respectively. This creates a favorable environment for Neisseria gonorrhoeae to grow clearly, which is essential when the specimen has mixed flora.

Other media like blood agar or MacConkey are nonselective or selective for different organisms and are overwhelmed by the normal flora present at these sites, making it harder to detect gonorrhea. Chocolate agar is enriched but not selective, so it doesn’t adequately suppress competing organisms. Thus, for accurate detection from pharyngeal or rectal sites, a selective Thayer-Martin culture is the best choice.