Comparison of two commercial assays for the characterization of rpoB mutations in Mycobacterium tuberculosis and description of new mutations conferring weak resistance to rifampicin

The aim of this study was to compare the efficiency of two commercial assays, INNO-LiPA Rif.TB and MTBDRplus, for the identification of mutations in the rpoB hot-spot region and to assess the efficiency of these mutations in conferring resistance to rifampicin. A collection of 126 rifampicin-resistant Mycobacterium tuberculosis and Mycobacterium africanum isolates and 18 rifampicin-susceptible isolates from different countries were analysed using the two hybridization assays. For 60 strains the hot-spot region of the rpoB gene was sequenced, confirming the results of the hybridization assays and allowing the identification of new mutations. In total, 17 mutations involving 10 codons were observed, two of which are newly described (D516Y and E562G/P564L). Mutations L533P, H526L, D516Y and L511P and the double mutation E562G/P564L conferred a low level of resistance. The assays INNO-LiPA Rif.TB and MTBDRplus identified rpoB mutations in 98.4% of cases. MTBDRplus provided additional information due to the overlapping hybridization probes and in addition allowed the investigation of katG mutations for isoniazid resistance.