A novel PCR-based reverse hybridization method Genotype MTBDR assay (Hain Lifescience GmbH, Nehren, Germany) was evaluated for rapid detection of rifampin (RIF) and isoniazid (INH) resistance in Turkish Mycobacterium tuberculosis isolates. The Genotype MTBDR assay is designed to detect mutations within the 81-bp hotspot region of rpoB and mutations at katG codon 315. A total of 41 RIF-resistant M. tuberculosis isolates with rpoB mutations that were previously tested by the INNO-LiPA Rif.TB kit and also characterized by DNA sequencing were included in the study. Thirty-seven of these isolates were also resistant to INH. RIF resistance was correctly identified in 39 of 41 isolates (95.1%) with the Genotype MTBDR assay probes specific for these mutations. One isolate with a Gln-490-His mutation and another one with a CGG insertion between codons 514 and 515 were identified as RIF sensitive by the Genotype MTBDR assay. While the INNO-LiPA Rif.TB kit was able to determine the CGG insertion between codons 514 and 515, the Gln-490-His mutation outside the 81-bp hotspot region was not detected by the INNO-LiPA Rif.TB kit. These isolates had MICs of >32 g/ml for RIF. The Genotype MTBDR assay also correctly identified 27 of 37 INH-resistant isolates (73%) with mutations in katG codon 315. In conclusion, the Genotype MTBDR assay may be useful for the rapid diagnosis of the most common mutations found in multidrug-resistant M. tuberculosis strains. However, the test results should always be confirmed with phenotypic methods.Mycobacterium tuberculosis remains one of the most significant causes of death from an infectious agent. The incidence of pulmonary tuberculosis in Turkey is nearly 30 per 100,000 population (2, 26). In the Aegean region, 8.2% of M. tuberculosis strains isolated between 1999 and 2001 were found to be resistant to rifampin (RIF). During the same period, the incidence of resistance to both RIF and isoniazid (INH) was 6.8% (8).Collectively, DNA sequencing studies demonstrate that more than 95% of RIF-resistant M. tuberculosis strains have a mutation within the 81-bp hotspot region of the rpoB gene (5,12,25). In contrast, the mutations causing INH resistance are located in several regions (28). Approximately, 34.6 to 94.3% of INH-resistant strains have been found to contain mutations in codon 315 of the katG gene (9,10,15,18,27), 2.9 to 21.5% contain mutations in the inhA promoter region (9,10,18,27), and an additional 2 to 11.5% have mutations in the ahpC-oxyR intergenic region (9, 10, 27).Several molecular methods have been developed in recent years to evaluate the rpoB and katG genes for RIF and INH resistance, including DNA sequencing, line probe assay, and analysis with DNA microarrays. Molecular assays have been established to allow the prediction of drug resistance in clinical M. tuberculosis isolates within one working day and potentially are the most rapid methods for the detection of drug resistance (5, 6, 9, 11, 12). The Genotype MTBDR assay (Hain Lifescience GmbH, Nehren, Germany) is a novel kit-...

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