Molecular characterization of rifampin-resistant isolates of Mycobacteriumtuberculosis from Hungary by DNA sequencing and the line probe assay

Two regions of rpoB associated with rifampin resistance were sequenced in 2 9 rifampin-resistant (determined by the proportion method) isolates of Myco bacterium tuberculosis obtained from patients from three counties in Hungar y. Of the 29 resistant strains, 27 had a mutation in either the 81-bp regio n (26 strains) or the N-terminal region (1 strain), while the other 2 strai ns had no mutations in either region. The locations and frequencies of the mutations differed from those previously reported. The most common mutation in this study, D516V, was found in 38% of the Hungarian strains, a frequen cy 2 to 10 times higher than that found in studies from other countries. Th ese same 29 isolates were also evaluated with the Inno-LiPA Rif. TB test (L iPA), a reverse hybridization assay for the rapid detection of rifampin res istance. Although LiPA detected the presence of an rpoB mutation in 26 of t he resistant isolates, the type of mutation could not be determined in 4 is olates because the mutations present were not among those included on the L iPA strip. In addition, a silent mutation in one of the rifampin-susceptibl e control strains was interpreted as rifampin resistant by LiPA. These find ings demonstrate the importance of validating this rapid molecular test by comparison with DNA sequence results in each geographic location before inc orporating the test into routine diagnostic work.