A patient with HIV and CD4 count of 30 cells/μL presents with disseminated infection — fever, hepatosplenomegaly, anemia, and positive blood culture. Ziehl-Neelsen staining of buffy coat reveals non-chromogenic AFB forming serpentine cords. Which mycobacterium species is most likely responsible?
- A Mycobacterium kansasii
- B Mycobacterium marinum
- C Mycobacterium avium complex (MAC) ✓
- D Mycobacterium scrofulaceum
Correct answer: C. Mycobacterium avium complex (MAC)
Explanation
Disseminated Mycobacterium avium complex (MAC) infection is the most common opportunistic mycobacterial infection in advanced HIV (CD4 <50 cells/μL). MAC forms beaded, non-chromogenic AFB and characteristically grows in serpentine cords in BACTEC blood culture bottles. It is resistant to standard TB drugs but responds to clarithromycin plus ethambutol, with or without rifabutin. M. kansasii causes pulmonary disease mimicking TB. M. marinum causes aquarium granuloma. M. scrofulaceum causes cervical lymphadenitis in children.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.