The slowly growing, orange-pigmented acid-fast bacillus associated with pediatric cervical lymphadenitis is most likely which species?

• A. Mycobacterium avium complex
• B. Mycobacterium chelonei
• C. Mycobacterium fortuitum
• D. Mycobacterium scrofulaceum

Answer: (D)

The main concept here is the link between the organism’s growth rate, pigment production, and the typical clinical presentation in children. Mycobacteria that cause pediatric cervical lymphadenitis are classically slow-growing and pigmented. The orange pigment described points to scotochromogenic mycobacteria, which produce pigment even in the dark. Among these, Mycobacterium scrofulaceum is the classic cause of cervical lymphadenitis (often called scrofula) in children, matching the slow growth and orange pigment.

Other options don’t fit as well for this presentation. Rapidly growing mycobacteria like M. chelonae and M. fortuitum typically cause skin and soft tissue infections after trauma or surgery, not the characteristic pediatric cervical lymphadenitis. Mycobacterium avium complex is another slow-growing group, but it is not the classic pigment-bearing culprit for this lymphadenitis presentation in children and is more often associated with disseminated disease in immunocompromised hosts or different clinical scenarios.

So the combination of slow growth, orange pigment, and the pediatric cervical lymphadenitis pattern points to the scotochromogenic Mycobacterium scrofulaceum.