Investigation of Gene Regions Responsible for Drug Resistance in Clinical Isolates of Mycobacterium tuberculosis Complex Resistant to at Least Two First-Line Anti-Tuberculosis Drugs

Early and rapid diagnosis of drug resistance in tuberculosis (TB) plays a key role in reducing the spread of resistance and enabling effective treatment. The aim of this study was to investigate mutations in drug resistance-associated gene regions of <i>Mycobacterium tuberculosis</i> complex (MTBC) isolates resistant to at least two first-line anti-tuberculosis drugs through sequence analysis, in order to characterize the core molecular features of these strains in the region and to identify previously unreported, geographically distinct novel mutation sites. The drug susceptibility of 23 clinical isolates was assessed using the BACTEC MGIT 960 system, and resistance-associated point mutations were identified through DNA sequence analysis and comparison with GenBank reference sequences. AAG → AGG mutation was detected in the <i>rpsL</i> gene region at codon 43 (<i>n</i> = 7) and codon 88 (<i>n</i> = 1). Additionally, GAG → GCG point mutation was identified at codon 70 (<i>n</i> = 2), representing a new region not previously reported in the literature. The most frequent mutation was AGC → ACC at <i>katG</i> codon 315 (<i>n</i> = 10), followed by a C → T substitution at position -15 of the <i>inhA</i> promoter region (<i>n</i> = 4). Additionally, TCG → TTG at <i>rpoB</i> codon 531 (<i>n</i> = 4) and ATG → GTG at <i>embB</i> codon 306 (<i>n</i> = 1) were detected. The detection of resistance-associated mutations is essential for controlling drug-resistant tuberculosis. In this study, a novel <i>rpsL</i> mutation (GAG → GCG) at codon 70 and a previously unreported codon 88 mutation in our country were identified, contributing to the understanding of molecular resistance mechanisms and epidemiology.