The slowly growing, orange-pigmented acid-fast bacillus isolated from cervical lymph nodes in a child with cervical adenitis is most likely which species?

The slowly growing, orange-pigmented acid-fast bacillus isolated from cervical lymph nodes in a child with cervical adenitis is most likely which species?

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

Answer: (D)

Cervical lymphadenitis in a child with a slowly growing, pigmented acid-fast bacillus points to a scotochromogenic Mycobacterium, which produces pigment in the dark. Mycobacterium scrofulaceum is classically associated with this presentation (scrofula) and forms orange-yellow pigment without needing light exposure. That combination of slow growth, pigmentation, and the cervical lymph node focus makes it the best match. Other mycobacteria can cause lymphadenitis or skin infections, but their growth rates and pigment patterns don’t align as closely with this scenario—for example, rapid-growing mycobacteria are more commonly linked to skin and soft tissue infections, and those not pigmented or pigmenting only after light exposure are less typical for pediatric cervical lymphadenitis.

Cervical lymphadenitis in a child with a slowly growing, pigmented acid-fast bacillus points to a scotochromogenic Mycobacterium, which produces pigment in the dark. Mycobacterium scrofulaceum is classically associated with this presentation (scrofula) and forms orange-yellow pigment without needing light exposure. That combination of slow growth, pigmentation, and the cervical lymph node focus makes it the best match.

Other mycobacteria can cause lymphadenitis or skin infections, but their growth rates and pigment patterns don’t align as closely with this scenario—for example, rapid-growing mycobacteria are more commonly linked to skin and soft tissue infections, and those not pigmented or pigmenting only after light exposure are less typical for pediatric cervical lymphadenitis.