A 22-year-old woman presents with cervical discharge and dysuria. NAAT (Aptima Combo 2 assay) on a cervical swab tests positive for both Neisseria gonorrhoeae and Chlamydia trachomatis. Culture for N. gonorrhoeae is requested. The selective medium for N. gonorrhoeae culture is:

• A Charcoal-yeast extract agar with L-cysteine — selective for fastidious intracellular pathogens
• B Modified Thayer-Martin (MTM) medium — chocolate agar with vancomycin, colistin, nystatin, and trimethoprim to suppress normal flora ✓
• C New York City (NYC) medium with lysed horse blood — supports growth of all Neisseria including non-pathogenic species
• D Bordet-Gengou agar with glycerol and blood — historically used for fastidious gram-negative diplococci

Explanation

Modified Thayer-Martin (MTM) medium is the standard selective medium for N. gonorrhoeae isolation from specimens with normal flora (genital specimens, pharyngeal swabs, rectal swabs). It is a chocolate agar base (enriched with IsoVitaleX/VCNT supplements) containing four antimicrobials: vancomycin (inhibits gram-positive bacteria), colistin (inhibits gram-negative rods), nystatin (inhibits fungi), and trimethoprim (inhibits swarming Proteus). N. gonorrhoeae is oxidase-positive and ferments glucose only (not maltose, lactose, or sucrose), distinguishing it from N. meningitidis (ferments glucose and maltose). Charcoal-yeast extract is for Legionella. Bordet-Gengou is for Bordetella pertussis.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.