Thayer-Martin (Chocolate) agar is primarily used to culture which organism?

• A. Chlamydia trachomatis
• B. Aspergillus
• C. Haemophilus influenzae
• D. Neisseria gonorrhoeae

Answer: (D)

Thayer-Martin chocolate agar is a selective, enriched medium designed to isolate Neisseria species, especially Neisseria gonorrhoeae. The chocolate base provides a rich mix of nutrients by lysing red blood cells, which fastidious organisms need to grow. The key feature is the antibiotic supplement—vancomycin, colistin, and nystatin (and sometimes additional agents)—which suppresses competing Gram-positive bacteria, many Gram-negative rods, and fungi. This selective pressure allows Neisseria gonorrhoeae, a fastidious gram-negative diplococcus, to grow from clinical specimens where other flora would overgrow.

Other organisms mentioned don’t fit as the primary target. Chlamydia trachomatis is an obligate intracellular organism and isn’t cultured on standard agar media like this. Aspergillus is a fungus grown on fungal media such as Sabouraud dextrose. Haemophilus influenzae does grow on chocolate agar because it requires X and V factors, but the antibiotic mix in Thayer-Martin is specifically chosen to favor Neisseria, making this medium primarily used for gonococcal culture.