Three days after a contaminated injection, a patient develops an erythematous nodule at the site that progresses to an abscess. Culture of pus yields acid-fast bacilli forming visible colonies on Löwenstein-Jensen medium within 4 days. Which organism is most likely?

• A Mycobacterium chelonae-abscessus group ✓
• B Mycobacterium avium complex
• C Mycobacterium scrofulaceum
• D Mycobacterium xenopi

Explanation

Rapidly growing mycobacteria form mature colonies on solid media within 7 days, unlike all other mycobacteria which need 2 to 8 weeks. The M. fortuitum, chelonae and abscessus groups are the classic rapid growers and cause post-injection abscesses, surgical wound and catheter-related infections. M. avium complex, M. scrofulaceum and M. xenopi are slow growers requiring weeks to appear in culture.

Reference: Jawetz, Melnick and Adelberg's Medical Microbiology, 28th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.