An immunocompetent patient with a history of aquarium fish handling presents with a chronic nodular ulcer on the right hand tracking up the forearm in a sporotrichoid pattern. Biopsy culture grows M. marinum. What is the preferred treatment?

• A Isoniazid + rifampicin for 6 months
• B Doxycycline monotherapy for 3 months
• C Clarithromycin + ethambutol for 3–6 months ✓
• D Ciprofloxacin monotherapy for 4 weeks

Explanation

Mycobacterium marinum ('fish tank granuloma') is a photochromogenic NTM that grows optimally at 30–32°C (not body temperature, hence superficial skin infection only in immunocompetent hosts). Sporotrichoid spread along lymphatics is characteristic. Preferred treatment is clarithromycin plus ethambutol for 3–6 months; some add rifampicin for extensive disease. The combination is used because M. marinum is intrinsically resistant to isoniazid and pyrazinamide. Standard anti-TB regimens are therefore ineffective.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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