Three days after receiving gluteal injections at an unlicensed clinic, a 30-year-old woman develops a tender fluctuant abscess. Aspirate stained by Ziehl-Neelsen shows acid-fast bacilli. Subculture on Lowenstein-Jensen medium shows growth within 6 days. Which statement about the likely organism is correct?

• A It belongs to Runyon group III and responds well to standard antitubercular drugs
• B It is an obligate intracellular pathogen that cannot grow on cell-free media
• C It is niacin positive and requires pyruvate-enriched medium for growth
• D It is a rapid grower and is usually resistant to conventional antitubercular therapy ✓

Explanation

Visible growth within about seven days identifies a rapidly growing mycobacterium such as M. fortuitum or M. chelonae (Runyon group IV), classic causes of post-injection and post-surgical abscesses. They are innately resistant to first-line antitubercular drugs and require agents like amikacin, fluoroquinolones, macrolides or imipenem based on susceptibility testing. Niacin positivity and obligate intracellularity describe M. tuberculosis, not this isolate.

Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.