GenoType MTBDRplus 1.0® for the detection of cross-resistance between isoniazide and ethionamide in isolates of multidrug-resistant Mycobacterium tuberculosis

Introduction: A variable proportion of isolates of multidrug-resistant Mycobacterium tuberculosis also presents resistance to ethionamide. It is important to determine whether resistance to isoniazid is independent or crossed with resistance to ethionamide, given that this could lead to the re-evaluation of second-line anti-tuberculosis treatment. The GenoType MTBDRplus (R) molecular test is used for the detection of MDR-MTB, as it identifies mutations associated with resistance to isoniazide and could detect cross-resistance with ethionamide. Objective: To evaluate the performance of GenoType MTBDRplus (R) in comparison with sequencing in the detection of mutations in gene katG and promotor inhA in clinical isolates of multidrug-resistant M. tuberculosis. Materials and methods: The GenoType MTBDRplus 1.0 (R) commercial kit and sequencing were used to evaluate mutations in gene katG and promotor inhA in 30 multidrug-resistant M. tuberculosis isolates that were resistant to ethionamide. The laboratory strain H37Rv and three pan-sensitive isolates acted as controls. Results: The kappa index for the comparison between the results of sequencing and GenoType MTBDRplus (R) was 1. All the isolates resistant to isoniazid and ethionamide had the mutations detected by GenoTypeMTBDRplus (R) in the katG gene and 40% of them in promotor inhA. Sequencing also revealed katG mutations in positions different to those detected by GenoType MTBDRplus (R). Conclusion: GenoType MTBDRplus (R) is able to detect resistance to isoniazid rapidly. Our results suggest that it could also be used to screen for cross-resistance with ethionamide.