Title : Phenotypic characterisation of non tuberculous mycobacterium species isolated from clinical specimens
Abstract:
Background: Non tuberculous bacteria (NTM) are increasingly recognised cause of pulmonary as well as extrapulmonary infection worldwide. This rising prevalence of NTM, particularly rapidly growing mycobacteria along with their inherent and acquired drug resistance, and species-specific antimicrobial susceptibility patterns pose major diagnostic and therapeutic challenges, particularly in tuberculosis endemic regions. Phenotypic characterization and antimicrobial susceptibility profiling remain essential for guiding appropriate clinical management& patient outcome.
Methods: The cross-sectional study comprises of total 3018 clinical specimens (pulmonary and extrapulmonary) submitted to Microbiology Laboratories. Zeihl-Neelsen (ZN) stain and mycobacterial culture on Bactec MGIT were carried out following decontamination and concentration of specimen. Culture positive isolates were differentiated phenotypically into Mycobacterium tuberculosis complex(MTBC) & NTM. NTM isolates were further characterised to complex/species level using line probe assay (LPA). Antimicrobial susceptibility testing was performed by broth microdilution for clinically relevant antibiotics following CLSI guidelines.
Results: Out of 3018 specimens, 607 (20.11%) were culture positive for mycobacterial growth, of which 125 (20.59%) were identified as NTM. The predominant isolate was M.abscessus complex (77.6%), followed by M.fortuitum complex (18.4%), Mycobacterium spp. (3.2%) and M.chelonae (0.8%). NTM were most frequently isolated form pus (44%), respiratory samples (28.8%), Tissue (17.6%), synovial fluid (8%), pleural fluid (1.6%). Drug susceptibility testing showed high susceptibility to amikacin (99.2%), tigecycline (85.6%), linezolid (81.6%) and clarithromycin (68.8%). High resistance rates were observed for cotrimoxazole (84%), doxycycline (68%), minocycline (58.4%), ciprofloxacin (52.8%) and moxifloxacin (52.8%).
Conclusion: The study highlights a substantial burden of NTM among culture positive specimens, with dominance of rapidly growing mycobacteria, particularly M.abscessus complex. The observed multidrug resistance underscores the importance of routine NTM identification and phenotypic susceptibility testing for appropriate clinical management. Phenotypic characterisation remains a valuable diagnostic approach, especially in resource-limited settings, while emphasizing the need for molecular confirmation and surveillance to guide effective treatment strategies and improved patient outcomes
