Results of molecular genetic study of m. Tuberculosis strains isolated from specimens of mdr-tb suspects in Ulaanbaatar, Mongolia in 2009-2010 / Монголын Анагаах Ухаан

ABSTRACT

Bacground DST by conventional methods takes several weeks, while early diagnosis of the disease and the rapid identification of resistant strains are essential for efficient treatment and control of the MDR strains. Rapid molecular testing of detecting MDR-TB is needed.Objective: The aim of this study was to assess performance of molecular line probe assay, Genotype16 MTBDRp/us, for rapid detection of RIF and INH resistance for M.Tuberculosis in Mongolia. The sensitivity and specificity of Genotype® MTBDRp/us to detect RIF and INH resistance-associated mutations in culture specimens and directly in smear-positive clinical specimens was examined and compared with conventional culture and drug susceptibility testing on solid medium.Material and Methods: The subjects of this study were 218 MDR-TB suspects aged 14-75 years from 8 districts in Ulaanbaatar city. The study was conducted from July 2009 to May 2010. The Genotype M. Tuberculosis drug resistance first line (MTBDR plus) assay (Hain Life-science, Nehren, Germany) was tested on directly on 41 sputum specimens and 109 clinical isolates.Results: The high correlation of the results from Genotype® MTBDRp/us and conventional drug susceptibility testing was obtained from this study. The results clearly show high performance of Genotype® MTBDRp/us with almost 100% accuracy for all the important indicators, such as sensitivity, specificity, positive and negative predictive values of detection of RIF and INH resistance. Some minor discrepancies were obtained in comparison with DNA sequencing results.Our study found that among high proportion for detection of RIF resistance, S531L mutation (MUT3 band) occurred the most commonly, with 80.0% of all RIF-resistant strains (83.6% of MDR) having the mutation. Other mutation in the 530-533 regions was common, as detected by the lack of binding to the WT8 probe in the absence of S531L mutation.In this study we observed that mutations in the promoter region of inhA gene played a major role (67.6 % (63.9% of MDR strains and 90% of INH-mono-resistant strains) had a mutation in the inhA.Conclusion: The Genotype® MTBDRp/us assay was demonstrated as a rapid, reliable and highly accurate tool for early detection of MDR-TB through examining smear positive cases enabling early start of appropriate therapeutic and public health measures to control of the spread of drug resistant M.tuberculosis in the population.