Background: A rise in multidrug-resistant tuberculosis (MDR-TB), which is defined as the resistance to the two most effective firstline therapeutic drugs, Isoniazid (INH) and Rifampin (RIF), threatens global public health worldwide. Resistance of Mycobacterium tuberculosis to INH results from mutations in several genes most commonly in katG gene, and resistance to RIF is due to mutations in rpoB gene. Therefore, rapid diagnosis of MDR-TB is of high importance in controlling the disease progress and outcome. The accurate detection of the resistant TB strains can be accelerated by developing molecular tests. Objectives: The aim of the present local study was to isolate MDR-TB from the patients who were the residents in the west of Iran and examination the frequency of MDR-TB between patients of Lorestan province for the first time and assess the mutations in the regions related to RIF/INH resistance via PCR and sequencing methods. Methods: In this study, 106 isolates of M. tuberculosis were selected in health centers of Lorestan, Iran from 2014 to 2017. After culturing M. tuberculosis isolates on Löwenstein-Jensen medium, classical susceptibility testing proportional method against INH and RIF was performed. After DNA extraction, PCR and sequencing were used to detect mutations related to RIF and INH resistance. Results: The results demonstrated 3.8%, 0.9%, and 0.9% frequency for INH + RIF, INH and RIF resistance, respectively. Importantly, 4 out of 6 isolates harbored mutations in codon290 of katG gene. Also, these isolates contained mutations in codon339 of rpoB gene. No mutation was observed in inhA gene of M. tuberculosis isolates. Conclusions: The results suggest that molecular techniques can be used as a rapid method for the identification of drug resistance in clinical isolates of M. tuberculosis. DNA sequencing has a high sensitivity for the detection of resistance mutations to RIF and INH in MDR-TB cases. Also, the results showed that the most frequent resistance associated-mutations occurred in codon290 of katG and codon 339 rpoB gene segments.
