Background: Due to the significant prevalence of tuberculosis (TB) in Mazandaran and Golestan provinces in northern Iran, we aimed to investigate the gene mutations in resistant Mycobacterium tuberculosis isolated from pulmonary TB patients in these provinces of Iran. Methods: In this cross-sectional study, sputum of patients with suspected tuberculosis were evaluated in the central TB laboratory of Golestan in a period of two years from 2017 to 2019. After growing the isolates on Lowenstein-Jensen medium, the antibiotic-resistant cases identified using the resistance ratio method. Then, the DNAs of the resistant isolates were extracted manually by the CTAB-Proteinase K method and investigated for gene mutations using PCR test and sequencing.Results: The mean age of 26 patients was 52 years, while smoking, addiction, and diabetes were more common risk factors. However, 4 isolates (15.38%) were resistant to antibiotics, while one (3.84%) of them was resistant to rifampin, and two isolates (7.69%) were resistant against isoniazid, whereas one other isolate (3.84%) exhibited a multidrug-resistant (MDR) phenotype. The MDR isolate had a mutation in codon 315 of the KatG gene resulting in the conversion of serine to threonine, and a mutation in the codon 450 of the rpoB gene, causing the alteration of serine to leucine. In the rifampin-resistant isolate, a mutation occurred at the same site converting serine to leucine. Conclusions: The low prevalence of antibiotic resistance in clinical isolates of Mycobacterium tuberculosis in this study indicates the appropriate treatment of the patients in this area, however, the prevalence of resistance to isoniazid was higher than rifampin. The more important point was that the single MDR isolate was identified in Mazandaran province.
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