Epidemiology of rapidly growing mycobacteria and antimicrobial susceptibility profile of Mycobacterium abscessus complex

PURPOSE: Rapidly growing mycobacteria (RGM) are emerging pathogens with considerable variation in epidemiology and antimicrobial susceptibility patterns. Accurate species identification and antimicrobial susceptibility testing (AST) are essential to guide appropriate therapy. This study evaluated the epidemiology of RGM and the antimicrobial profile of the Mycobacterium abscessus complex (MABC). METHODS: A retrospective study was conducted from June 2013 to May 2025 at a tertiary care hospital in Mumbai. Clinical specimens were cultured using standard methods. RGM were identified by sequencing and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). AST for MABC was performed by broth microdilution (BMD) according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Inducible clarithromycin resistance (ICR) was also assessed. RESULTS: Sixty-eight RGM isolates were identified, most from patients aged 60-80 years, with a female predominance (58.8%). Pus and tissue were the most frequent specimen types (41.2%). MABC was the predominant species (67.65%), followed by M. fortuitum (14.71%). MABC showed high susceptibility to amikacin (91.1%), moderate activity to linezolid (37.8% susceptible, 42.2% intermediate), and 80% intermediate susceptibility to imipenem and cefoxitin. Resistance was high to cotrimoxazole, ciprofloxacin, and doxycycline. ICR was detected in 26.6% of tested MABC isolates. CONCLUSION: MABC is the predominant RGM in this setting and demonstrates high susceptibility to amikacin, with moderate activity of linezolid. ICR, tested and found in a subset of isolates, underscores the need for subspecies identification to optimize treatment. AST performed using recommended methods will help to guide therapy and formulate antimicrobial policy for managing these difficult to treat pathogens.