Nontuberculous mycobacteria in Mumbai: Species distribution and susceptibility

Non-tuberculous mycobacteria (NTM) infections are globally prevalent, yet species distribution and antibiotic susceptibility vary considerably across regions. In India, limited epidemiological data have led to treatment practices based largely on western guidelines.

This retrospective observational study aims to generate data on the distribution of NTM species and species-specific antibiotic susceptibility patterns at our centre, and to compare these findings with both local and international data to improve treatment outcomes.

A 9-year retrospective observational study was conducted at our institute in Mumbai, India, from June 2014 to June 2023. A total of 891 NTM isolates were analyzed-728 (81.7%) rapidly growing mycobacteria (RGM) and 163 (18.3%) slow-growing mycobacteria (SGM). Speciation was performed for 68.2% of RGM isolates, and antimicrobial susceptibility testing was done using standardized protocols.

Among RGM, M. abscessus, M. fortuitum, and M. chelonae were predominant. High susceptibility rates were observed to amikacin (100%) and linezolid (M. abscessus 100%, M. fortuitum 100%, M. chelonae 95%). Clarithromycin susceptibility was 90% for M. abscessus, 78% for M. fortuitum, and 90% for M. chelonae. M. fortuitum showed significantly higher susceptibility to quinolones (90% vs <20% for other species). Susceptibility to clarithromycin, linezolid, imipenem, and tobramycin differed notably from western data.

RGM susceptibility patterns vary significantly between and within countries, underscoring the need for regional antimicrobial surveillance and India-specific treatment guidelines.

Speciation was done for 68.2% of RGM isolates, and inducible macrolide resistance testing was included only after 2017. Clinical correlation was unavailable for a few isolates; hence, colonization could not be ruled out for some respiratory samples. SGM susceptibility data was not available.