Novel mutation in efflux pump Rv1258c (Tap) gene in drug resistant clinical isolates of Mycobacterium tuberculosis in Iran.

INTRODUCTION: Tuberculosis (TB) remains a serious public health problem worldwide. Drug-resistant TB is considered a major and growing global threat. Despite the great variety of described mutations in Mycobacterium tuberculosis (MTB) resistance genes, the mechanisms of drug resistance are still controversial. Recently, a report on the role of efflux pump genes in drug resistance added to this complexity. Therefore, a thorough understanding of efflux pump genes in drug-resistant TB clinical isolates is needed. METHODOLOGY: We performed molecular analysis of the efflux pump gene (Rv1258c) in 33 drug-resistant and 20 drug-sensitive clinical MTB isolates by sequencing the amplicons' targets in both the forward and reverse directions. RESULTS: A novel mutation of the Rv1258c gene was identified at G442A (Ala148Thr) in rifampicin mono-resistant clinical strain, as compared to the H37Rv reference strain. In addition, a cytosine nucleotide insertion was found between the positions 580 and 581 (denominated Tap580) in two drug-sensitive strains at identical gene positions. CONCLUSIONS: These results indicated the possibility of mutation in the efflux pump genes and the important role of Tap efflux pump genes in drug-resistant MTB isolates. However, further research is required to determine the direct association of these mutations with resistant MTB.

Significance of the coexistence of non-codon 315 katG, inhA, and oxyR-ahpC intergenic gene mutations among isoniazid-resistant and multidrug-resistant isolates of Mycobacterium tuberculosis: a report of novel mutations.

Tuberculosis (TB) is a global threat due to the emergence and spread of drug-resistant Mycobacterium tuberculosis (MTB). Isoniazid (INH) is the main antibiotic used for prevention and treatment of TB. Evidence shows that accumulated mutations can produce INH resistant (INHR) strains, resulting in the progression of multidrug-resistant (MDR) TB. Since point mutations in katG gene, inhA gene, and oxyR-ahpC region correlated with the INH resistance, in this study, we aimed to identify mutations in these three genes in INHR and MDR clinical isolates of MTB by Sanger DNA sequencing analysis. Thirty-three out of 438 isolates were resistant, including 66.7% INHR and 30.3% MDR isolates. In the katG gene, 68.2% INHR isolates had non-synonymous point mutations, mainly R463L (63.6%), and non-synonymous point mutation KatG L587P was seen in one of the MDR isolate. A novel silent substitution L649L was identified in the inhA gene of the MDR isolates. The oxyR-ahpC intergenic region g-88a common mutations (63.6%) in INHR and two distinct novel mutations were found at positions -76 and -77 of the oxyR-ahpC intergenic region. The coexistence of katG non-codon 315 with oxyR-ahpC intergenic region mutations was highly frequent in INHR 59.1% and MDR isolates 70%. Since mutations of all three genes 95.5% lead to the detection of INHR, they might be useful for molecular detection. Our results indicated the continuous evolution and region-specific prevalence of INH resistance. Overall, identification of new mutations in INH resistance can improve the available strategies for diagnosis and control of TB.