Comparison of performance of two DNA line probe assays for rapid detection of multidrug-resistant isolates of Mycobacterium tuberculosis.

Infections with multidrug-resistant (resistant at least to rifampicin, RIF and isoniazid, INH) strains of Mycobacterium tuberculosis (MDR-TB) are associated with high case fatality rates. Rapid identification' of MDR-TB strains is important for early institution of appropriate therapy. Two DNA line probe assays, GenoType MTBDR (GT-MTBDR) and INNO-LiPA Rif. TB (INNO-LiPA) were compared for their abilities to detect resistance to INH and RIF in 80 M. tuberculosis isolates. The test results were compared to those obtained by conventional drug susceptibility testing (DST), DNA sequencing and/or PCR-restriction fragment length polymorphism (RFLP) analysis of regions of interest of M. tuberculosis genome. Compared to the DST and katG codon 315 PCR-RFLP results, GT-MTBDR test results were concordant for INH resistance for 63 of 80 (78.7%) isolates. For RIF resistance, GT-MTBDR and INNO-LiPA test results were concordant with DST for 74 of 80 (92.5%) and 76 of 80 (95%) strains, respectively. The GT-MTBDR test results correlated with sequencing results for 77 of 80 (96.2%) while INNO-LiPA results for 79 of 80 (98.7%) isolates. Both the tests are useful for rapid detection of MDR-TB strains, however, GT-MTBDR assay offers the advantage of detecting the resistance to both INH and RIF simultaneously when MDR-TB is suspected.