Study of Mutations Associated with Isoniazid-Resistance in Clinical Mycobacterium Tuberculosis Strains, Tehran and Isfahan Province Tuberculosis Centers by PCR and RFLP-Based Technique (2004-5)

Background & Objectives: Although isoniazid is the most efficient in killing the tuberculosis bacilli, resistance to this drug also develops most readily. Mutations in katG, inhA and ahpC are responsible for isoniazid resistance in a large proportion of tuberculosis cases. The frequency of these mutations varies with population samples, however. This study provided the first molecular characterization of Isoniazid-resistance in M. Tuberculosis strains that is widely applicable for rapid drug resistance detection.

Materials and Methods: The study was a descriptive and analytical and the presence of mutations in specific regions of the katG, inhA and ahpC genes was analyzed in 32 M. tuberculosis Isoniazid-resistant strains in Isfahan and Tehran. To determine the mutations in codon 315 of katG, PCR-RFLP technique was performed. In this way, 355 bp PCR products were digested by MspI and MspA1I. Mutations in inhA and ahpC genes were detected by sequencing.

Results: The frequency of mutations in the katG 315(Ser→Thr), inhA and ahpC were detected in 71.9%, 18.9% and 6.2% of the 32 Isoniazid resistant isolates, respectively. Mutation was not found in one of the isolates.

Conclusion: The PCR-RFLP with MspI, being able to detect katG Ser315Thr substitution, can identify 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. The results also suggest that the detection of the Ser315Thr in the katG gene may be used as a rapid screening method for identifying Isoniazid-resistant clinical M.tuberculosis isolates recovered from Isfahan and Tehran tuberculosis centers.