A 6-year-old rural child presents with painless left cervical lymphadenopathy of 3 months duration. Biopsy shows caseating granulomas and AFB are demonstrated. Culture grows acid-fast bacilli that are niacin negative and nitrate reductase negative. The child drinks raw cow milk. Which organism is most likely?
- A Mycobacterium tuberculosis
- B Mycobacterium bovis ✓
- C Mycobacterium avium complex
- D Mycobacterium scrofulaceum
Correct answer: B. Mycobacterium bovis
Explanation
Mycobacterium bovis causes scrofuloderma and cervical lymphadenitis in children who consume unpasteurized milk. Unlike M. tuberculosis, it is niacin negative and nitrate reductase negative, and it is naturally resistant to pyrazinamide. M. tuberculosis is niacin positive and nitrate positive. M. avium complex and M. scrofulaceum also cause paediatric cervical adenitis, but the history of raw milk consumption plus the biochemical profile points specifically to M. bovis.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.