Molecular Epidemiology of Non-Tuberculous Mycobacteria Among Tuberculosis-Suspected Patients in Iran: Species Distribution and Drug Resistance

In high-burden tuberculosis (TB) settings such as Iran, non-tuberculous mycobacteria (NTM) are increasingly identified among presumptive TB cases. However, their epidemiology and drug resistance patterns remain inadequately described. This study investigated the prevalence, species distribution, and antimicrobial susceptibility of NTM isolates from 3,000 clinical specimens collected from patients with presumptive TB at the Pasteur Institute of Iran between March 2022 and March 2023. Identification was performed through culture and sequencing of the <i>16S rDNA</i>, <i>rpoB</i>, and <i>hsp65</i> genes. Drug susceptibility testing (DST) was conducted using the broth microdilution method in accordance with Clinical and Laboratory Standards Institute guidelines. Among 145 acid-fast bacilli-positive cultures, 45 (31%) were identified as NTM. The predominant species were <i>Mycobacterium fortuitum</i> (51.1%) and <i>M. simiae</i> (40.0%), followed by less common isolates of <i>M. abscessus</i>, <i>M. kansasii</i>, and <i>M. flavescens</i>. The majority of NTM isolates (86.7%) originated from respiratory specimens. Phenotypic analyses revealed high resistance rates to first-line anti-TB drugs such as isoniazid and rifampicin, while susceptibility varied across fluoroquinolones, aminoglycosides, and sulfonamides. These findings underscore the importance of species-level identification and DST-guided therapy to improve the clinical management of NTM infections in TB-endemic regions.