Aim and Background. The aim of this study was to investigate the frequency, location and type of rpoB mutations in Mycobacterium tuberculosis isolated from patients in Tehran City.

Materials and Methods. 65 sputums were collected from suspected tuberculosis patients, 35 Rif-r isolates were identified as Mycobacterium tuberculosis. PCR Amplification and DNA sequencing methods were performed. 411 bp fragments of rpoB gene were sequenced and mutations in 81 bp regions were analyzed.

Results. 38 mutations were identified in 14 RIF-r MBT (70%). Missense mutations produced 38 types of amino acid substitutions. In 6 RIF-r MBT isolates (30%) no mutations were found in the core region of the rpoB gene. Most frequent mutations detected from Tehranian strains were in codons 531 and 515. Two alleles in codon 531 and one allele in all codons 526, 515, 510, 566, 490 and 476 were found. In the 6 isolates were identified 2 mutation in different codons and 8 strains harboured single mutations in codons .

Conclusion. In this study, has been investigated the significance of mutations in the rpoB gene, its correlation with genotype and phenotype agents and high level of resistance to rifampicin in 14 isolates of M. tuberculosis collected from patients with active pulmonary tuberculosis from different geographic regions of Tehran.