Which laboratory test is used to diagnose gonorrheal pharyngitis or proctitis?

• A. Thayer-Martin culture
• B. PCR testing for Neisseria
• C. Gram stain of throat culture
• D. Culture on blood agar

Answer: (A)

Gonorrheal infection in the throat or rectum is diagnosed by growing Neisseria gonorrhoeae on a selective culture medium that suppresses other bacteria. Thayer-Martin culture, a modified selective medium, contains antibiotics that inhibit competing flora while allowing gonococcus to grow, making it the best option for isolating the organism from pharyngeal or proctal specimens. This approach is also valuable because it provides isolates for antimicrobial susceptibility testing, which is important given evolving resistance patterns. While PCR testing can detect Neisseria gonorrhoeae DNA directly and is widely used, culture on selective media remains the method that enables confirmation and susceptibility data from these sites. Gram stain of throat specimens is unreliable for pharyngeal gonorrhea due to mixed flora and lower sensitivity in the throat, and blood agar is nonselective and not used for this purpose.