Performance of genotype-MTBDR test directly on clinical specimens

Objectives: Most important point for the control and effective treatment of multidrug resistant tuberculosis (MDR-TB)is early diagnosis and rapid determination of the resistance. The aim of this study is to assess the performance of theGenotype-MTBDR assay applied directly on sputum samples and compare the results with those obtained by DNA sequencingand phenotypic susceptibility testing.Materials and methods: Between November 2005 and February 2006, 93 smear and culture positive sputum sampleswere included in the study. Drug susceptibility results for rifampin (RIF) and isoniazid (INH), obtained by proportionmethod on L-J medium, Genotype-MTBDR and DNA sequencing were compared.Results: The rate of concordance between the results of the Genotype-MTBDR and DNA sequencing was 93.5% and96.7% for RIF and INH, respectively. Moreover, Genotype-MTBDR detected all the RIF (24) and INH (18) resistant strainsobtained by sequencing (100%). Compared to the DNA sequencing method; the sensitivity, specificity, positive predictiveand negative predictive value for RIF and INH were 100%, 91.3%, 80%, 100% and 100%, 96%, 85.7%, 100% respectively.Conclusion: Genotype-MTBDR, one of molecular assays, distinctly shortens the time for diagnosis and detection of resistanceto INH and RIF, essential for management of MDR-TB. The test appears to have good sensitivity and specificitywhen also used directly on sputum specimens. J Microbiol Infect Dis 2012; 2(4): 135-141Key words: Mycobacterium tuberculosis; drug resistance; genotype-MTBDR.