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ABSTRACT Background and Aim: Isoniazid is one of the essential first line drugs in TB treatment. Resistance rate to this drug is increasing in many parts of the world. Mutations in KatG and inhA genes are frequently the cause of resistance of mycobacterium TB to INH. The aim of this study was to find a precise method for early detection of mutations associated with resistance of mycobacterium TB to INH. Materials and Methods: After performing sensitivity tests, presence of mutations in special loci of katG and inhA genes in 90 specimens obtained from positive cultures of TB patients was investigated. PCR-RLFP method was used to detect mutations in katG 315 codon. The PCR product resulting from the reproduction of this genetic segment (620 bp) was digested by restriction enzyme MspI. To identify mutations in inhA gene, MAS-PCR technique was used. Results: 34.5% of the INH resistant strains had Thr315 phenotype and 65.5% had Ser 315 phenotype. Thr 315 is 100% specific for determination of INH resistant isolates. Among 52 resistant isolates, 34.6% had Arg and 65.4% had Leu in codon 463. The frequencies of mutations in the (-15C → T) locus of inhA gene were 20% and 16.7% in MDR and Non MDR isolates respectively. Conclusions: By using PCR-RFLP with restrictive enzyme and MAS PCR mutations in codon 315 of KatG gene and promoter location of inhA gene can be identified. These methods are simpler and cheaper than other methods and provide early accurate and reliable results. Key words: Mycobacterium tuberculosis, Isoniazid resistance, PCR-RFLP, KatG, inhA. Conflict of Interest: Nill Received: Dec 30, 2009 Accepted: Feb 7, 2010

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ABSTRACT Background and Aim: A large number of factors are involved in the development of TB, but the most important one belongs to the host genetic factors. One of the genetic factors is cytokine gene polymorphisms. The results of recent studies indicate that IL-12 and IFN-γ play a central role in regulating the type and level of immune response in mycobacterial infections. Mutations in these genes may be associated with susceptibility to pulmonary TB. The aim of this study was to investigate the frequencies of IFN- γ (2109), IFN-γ R1 (-611) and IL-12B (-1188) genes polymorphisms and their relationships with susceptibility to pulmonary TB in Iranian population. Material and Methods: This was a case-control study. Thirty TB patients with positive smears hospitalized in TB departments of Masih Daneshvari Hospital and 30 healthy controls with no history of TB were selected for this study. Genotypes of IFN- γ (2109), IFN-γ R1 (-611) and IL-12B (-1188) genes were determined by using PCR-RFLP method. The PCR-products were analyzed by use of restriction enzymes. The data were analyzed by means of SPSS and Hardy – Weinberg equilibrium. Results: Considering IFN-γ R1 (-611) and IL-12B (-1188) genes there was a significant difference between the control and study groups (P < 0.05), but in regard to IFN- γ (2109), this difference was not detected between the two groups. Conclusion: Mutation in the regions of -611 of IFN-γ R1 and -1188 of IL-12B genes may increase the host susceptibility to mycobacterium tuberculosis and genotyping of these regions can be used for screening of the high risk individuals. Key words: Polymorphism, Pulmonary Tuberculosis, IL-12B, IFN-γ, IFN-γ. Received: Sep 3, 2011 Accepted: Feb 8, 2012