A 26-year-old woman develops a painful fluctuant abscess at the site of a gluteal intramuscular injection given ten days ago. Pus culture grows acid-fast bacilli that form visible colonies on Lowenstein-Jensen medium within five days. The most likely causative organism is:

• A Mycobacterium tuberculosis
• B Mycobacterium bovis
• C Mycobacterium kansasii
• D Mycobacterium fortuitum ✓

Explanation

Rapidly growing mycobacteria such as M. fortuitum, M. chelonae, and M. abscessus form mature colonies within seven days, unlike slow growers which need two to eight weeks. They cause post-injection abscesses, surgical wound infections, and catheter-related infections, often traced to contaminated instruments or water. M. tuberculosis takes weeks to grow, M. kansasii is a slow-growing photochromogen causing pulmonary disease, and M. bovis is a slow grower acquired via milk.

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.