Seed Reza Moaddab - Tuberculosis and Lung Research Centre and Paramedical Faculty, Tabriz University of Medical Sciences, Tabriz, Iran
Safar Farajnia - Biotechnology Research Centre, Tabriz University of Medical Sciences, Tabriz, Iran
Davood Kardan - Infectious and Tropical Disease Research Centre, Tabriz University of Medical Sciences, Tabriz, Iran
Sajad Zamanlou - Immunology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
Mohammad Yousef Alikhani - Microbiology department, Faculty of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran

Objective(s) Isoniazid (INH) is one of the main first line drugs used in treatment of tuberculosis and development of resistance against this compound can result in serious problems in treatment procedures. Resistance to INH is mediated mainly by mutation in KatG gene that is coded for the catalase enzyme. The proportional method for detection of INH-resistance is time consuming due to the slow growth rate of Mycobacterium tuberculosis. In this study, we used PCR-RFLP approach for screening of common mutations in KatG gene for detection of INH resistance, and compared the results to minimal inhibitory concentration (MIC) in M. tuberculosis isolates. Materials and Methods Fifty M. tuberculosis isolates were subjected to study of which, ۲۵ strains were INH-resistant and ۲۵ strains were INH-sensitive. Results Of ۲۵ INH-resistant strains, the mutation was identified in ۵۶% and ۲۰% in the KatG۳۱۵ and KatG۴۶۳ loci, respectively. In ۲۴% of INH-resistant strains, no mutation was observed in the studied loci. INH MIC was <۰.۲ pg/ml in all sensitive strains whereas among ۲۵ INH -resistant isolates, INH MIC was higer than ۰.۲ pg/ml ranged from ۰.۲ to ۳.۲ pg/ml. Conclusion Our findings revealed that PCR-RFLP is capable to identify INH-resistance in more than ۷۶% of INH- resistant M. tuberculosis strains, and could be used for rapid identification of INH resistance. High levels of INH MIC were observed in the strains which had mutation in the KatG gene in position ۳۱۵.

Isoniazid Resistance, Kat G, Mycobacterium tuberculosis, PCR, RFLP