A renal transplant recipient on tacrolimus develops multiple painful violaceous skin nodules over the limbs. Biopsy shows AFB, but cultures on standard Lowenstein-Jensen and liquid media remain sterile after 8 weeks. Repeat culture using medium supplemented with ferric ammonium citrate finally yields growth after 4 weeks. Which mycobacterium requires exogenous iron for growth?
- A Mycobacterium szulgai
- B Mycobacterium malmoense
- C Mycobacterium haemophilum ✓
- D Mycobacterium simiae
Correct answer: C. Mycobacterium haemophilum
Explanation
Mycobacterium haemophilum has an absolute requirement for iron supplied as hematin or ferric ammonium citrate, so it fails to grow on ordinary media unless supplemented, leading to false-negative reports. It prefers lower temperatures around 30 degrees A and causes nodular or ulcerative skin lesions mainly in immunosuppressed patients, exactly as described here. M. malmoense and M. szulgai grow without iron supplementation, and M. simiae is a rare scotochromogen associated with water sources.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.