A 35-year-old HIV-positive man (CD4 = 80/µL) develops fever, night sweats and extensive lymphadenopathy. Blood cultures grow mycobacteria in the BACTEC system. The organism is non-chromogenic, grows at 37°C, and is resistant to isoniazid and pyrazinamide but sensitive to clarithromycin and ethambutol. Which organism is most likely?
- A Mycobacterium avium complex (MAC) ✓
- B Mycobacterium tuberculosis (MDR-TB)
- C Mycobacterium kansasii
- D Mycobacterium marinum
Explanation
Mycobacterium avium complex (MAC) is the most common disseminated non-tuberculous mycobacterial (NTM) infection in advanced AIDS (CD4 <50/µL). It is non-chromogenic (Runyon Group III), grows at 37°C, is naturally resistant to isoniazid, pyrazinamide and often rifampicin, but susceptible to clarithromycin (first-line) and ethambutol. Disseminated MAC presents with fever, weight loss, night sweats, and elevated alkaline phosphatase. M. kansasii (Runyon IIA photochromogen) causes pulmonary disease resembling TB and is usually INH-sensitive. M. marinum causes swimming pool granuloma at cooler sites.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.