A slowly growing, orange-pigmented acid-fast bacillus isolated from a cervical lymph node in a child with cervical adenitis—most likely etiologic agent?

• A. M. scrofulaceum
• B. M. chelonei
• C. M. avium-intracellulare complex
• D. M. fortuitum

Answer: (A)

This scenario points to a Mycobacterium that grows slowly and develops an orange pigment when exposed to light, which is classic for a photochromogenic, slow-growing mycobacterium causing cervical lymphadenitis in children. Mycobacterium scrofulaceum fits this pattern and is the organism historically linked to scrofula (cervical lymphadenitis) in kids. The orange pigment helps differentiate it from other mycobacteria that are nonpigmented or rapidly growing. While Mycobacterium avium-intracellulare can also cause pediatric lymphadenitis, it isn’t the orange-pigmented, slow-growing type described here, and rapidly growing species like M. fortuitum or M. chelonei do not match the pigment and growth characteristics. Thus the best match is M. scrofulaceum.