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 the Genotype-MTBDR assay applied directly on sputum samples and compare the results with those obtained by DNA sequencing and phenotypic susceptibility testing. Materials and methods: Between November 2005 and February 2006, 93 smear and culture positive sputum samples were included in the study. Drug susceptibility results for rifampin (RIF) and isoniazid (INH), obtained by proportion method 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% and 96.7% for RIF and INH, respectively. Moreover, Genotype-MTBDR detected all the RIF (24) and INH (18) resistant strains obtained by sequencing (100%). Compared to the DNA sequencing method; the sensitivity, specificity, positive predictive and 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 resistance to INH and RIF, essential for management of MDR-TB. The test appears to have good sensitivity and specificity when also used directly on sputum specimens. J Microbiol Infect Dis 2012; 2(4): 135-141