ABSTRACT
Drug resistance to tuberculosis is increasing continuously and is a significant threat to tuberculosis control programs because there arc few drugs effective against Mycobacterium tuberculosis. Although isoniazid is most efficient in killing the tuberculosis bacilli, resistance to this drug also develops most readily. Mutations in katG, in particular the Ser 315 Thr substitution, are responsible for isoniazid resistance in a large proportion of tuberculosis cases. However, the frequency of the katG Ser 315 Thr substitution varies with population samples. This study provided the first molecular characterization of isoniazid resistance of M. tuberculosis strains and extended our knowledge of molecular basis of M. tuberculosis drug resistance that are widely applicable for rapid drug resistance detection. Using 1% proportional method, the sensitivity of 126 strains collected from Isfahan and Tehran to isoniazid was determined. The katG mutations in codon 315 associated with isoniazid resistance among isoniazid resistant isolates were determined by PCR-RFLP. In this way, 355 bp PCR products were digested by Mspl of 126 isolates of M. tuberculosis, 32 [25.4%] strains were determined as INH resistant. Resistance rate was 22.6% [19 strains] in Isfahan and 31% [13 strains] in Tehran. In total, 72% of isoniazid-resistant isolates could be identified by analysis of just katG 315 loci. The PCR-RFLP with Mspl that detect katG Ser315Thr substitution identified more isoniazid-resistant strains with mutations at codon 315 in the katG. Elucidation of the molecular basis of isoniazid resistance in M. tuberculosis has led to the development of different genotypic approaches for the rapid detection of isoniazid resistance in clinical isolates