TITLE:
Epidemiology and Antimicrobial Susceptibility of Slow-Growing Non-Tuberculous Mycobacteria in a TB-Endemic Setting: An 8-Year Laboratory-Based Study from North India
AUTHORS:
Puneeta Singh, Shalabh Malik, Vandana Lal
KEYWORDS:
Non-Tuberculous Mycobacteria (NTM), Slow-Growing Mycobacteria (SGM), Antimicrobial Susceptibility, Non-Tuberculous Mycobacterial Pulmonary Disease (NTM-PD), Mycobacterium avium Complex (MAC), MALDI-TOF, TB Endemic Setting
JOURNAL NAME:
Journal of Tuberculosis Research,
Vol.14 No.2,
June
5,
2026
ABSTRACT: Background: Differentiating non-tuberculous mycobacteria (NTM) from Mycobacterium tuberculosis remains a significant diagnostic challenge in tuberculosis (TB)-endemic settings, often leading to misdiagnosis and inappropriate therapy. Data on the epidemiology and antimicrobial susceptibility of slow-growing mycobacteria (SGM) in North India remain limited. This study aimed to characterize the prevalence, species distribution, and in vitro antimicrobial susceptibility patterns of SGM isolated from clinical specimens in a TB-burden setting. Methods: A retrospective laboratory-based study was conducted on clinical specimens processed between January 2018 and December 2025 at a tertiary reference laboratory in Delhi, India. Mycobacterial cultures were performed using liquid (MGIT 960) and solid (Lowenstein-Jensen) media. Species identification was carried out using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Antimicrobial susceptibility testing (AST) was performed on a subset of isolates using broth microdilution in accordance with Clinical and Laboratory Standards Institute (CLSI) guidelines. Temporal trends were assessed using the Cochran-Armitage test and Joinpoint regression analysis. Results: Of 197,943 clinical specimens processed, 34,776 (17.5%) yielded mycobacterial growth; of these, 30,343 (87.3%) were identified as members of the Mycobacterium tuberculosis complex, while 4433 (12.7%) were classified as NTM. Among these, 1845 (41.6%) were slow-growing mycobacteria (SGM) species. Pulmonary specimens accounted for the majority of SGM isolates (63.2%). The Mycobacterium avium complex (MAC) predominated, with M. chimaera representing 51.7% of SGM isolates, followed by M. simiae (13.0%) and M. kansasii (12.7%). Non-chromogenic species constitute 67.8% of isolates. Antimicrobial susceptibility testing (n = 204) demonstrated high in vitro activity of amikacin (99.5%) and clarithromycin (97.5%), followed by linezolid (95.2%) and moxifloxacin (94.6%), whereas comparatively higher resistance rates were observed for doxycycline, ciprofloxacin, and minocycline. Temporal analysis showed year-to-year variability without a statistically significant trend (annual percent change +0.15%; p = 0.963), indicating a stable proportional burden of NTM over time. Conclusions: This laboratory-based study highlights the persistent and diverse presence of slow-growing NTM in a TB-endemic setting, with MAC predominance across pulmonary and extrapulmonary specimens. The findings underscore ongoing diagnostic challenges and the importance of accurate species identification. However, the absence of clinical correlation necessitates cautious interpretation. Prospective studies integrating microbiological, clinical, and radiological data are essential to define the true burden and clinical significance of NTM disease.