Use of genotype MTBDR assay for molecular detection of rifampin and isoniazid resistance in Mycobacterium tuberculosis clinical strains isolated in Italy

Abstract

Mycobacterium tuberculosis is one of the leading causes of death worldwide, and multidrug-resistant tuberculosis (MDR-TB) is associated with a high case fatality rate. Rapid identification of resistant strains is crucial for the early administration of appropriate therapy, for prevention of development of further resistance, and to curtail the spread of MDR strains. The Genotype MTBDR (Hain Lifescience, Nehren, Germany) is a reverse hybridization line probe assay designed for the rapid detection of rpoB and katG gene mutations in clinical isolates. The ability of this technique to correctly identify resistant and MDR-TB strains was tested on 206 isolates from the Italian drug resistance surveillance system. This panel included the majority of MDR strains isolated in Italy in the past 3 years. The results of the test were compared to conventional drug susceptibility test performed on isolated strains and verified by sequencing the regions of interest of the bacterial genome. The rate of concordance between the results of the MTBDR and those obtained with "in vitro" sensitivity was 91.5% (130 of 142) for rifampin and 67.1% (116 of 173) for isoniazid. We also applied this test directly to a panel of 36 clinical specimens collected from patients with active TB. The MTBDR correctly identified the two cases of MDR-TB included in the panel. These results show that the MTBDR test is useful in the detection and management of tuberculosis when MDR disease is suspected.

FIG. 1.

Schematic representation of rpoB “hot-spot region” showing the positions of wild-type and mutated probes present in the strip. The average size of the probes is 20 bases. The arrowheads indicate the numbers and positions of omitted codons.

FIG. 2.

Mutations found in the rpoB “hot-spot region” of 142 M. tuberculosis strains. The arrowheads indicate the numbers and positions of omitted codons.