Introduction: Extensively drug-resistant tuberculosis (XDR-TB) and pre-XDR-TB are a major challenge to TB control due to their complex diagnosis and obstacles in treatment. With LiquidArray® MTB-XDR VER 1.0 Hain Lifescience provides an assay for rapid diagnosis of XDR-TB. Besides detection of Mycobacterium tuberculosis complex (MTBC) and its mutations conferring resistance to fluoroquinolones, amikacin, and ethambutol, the assay can also detect the most significant mutations conferring resistance to the group A drug Linezolid. Due to its ability to detect linezolid resistance, LiquidArray MTB-XDR VER 1.0 is currently the only assay available that detects XDR-TB according to the revised WHO definition.

Methods: As starting material patient specimens and cultivated samples are used. DNA extraction is performed manually or automated with the GenoXtract® fleXT nucleic acid extraction system allowing high sample throughput with minimal hands-on time. Amplification, detection, and automated result interpretation is performed in the FluoroCycler® XT system within one single tube.

Results: LiquidArray MTB-XDR VER 1.0 was evaluated according to IVDR requirements. Within the analytical study an excellent performance of the assay could be demonstrated for all parameters investigated, such as analytical sensitivity, precision, analytical specificity, etc. All mutations detectable by the assay conferring resistance to specific group A and group C drugs (fluoroquinolone, amikacin, ethambutol, and linezolid) were identified 100% correctly. The excellent performance of the assay could be also demonstrated within the clinical study. In this highly complex study high sensitivities and excellent specificities for detection of MTBC could be achieved, overall and for smear negative samples. The LiquidArray MTB-XDR VER 1.0 showed excellent performance for resistance detection of the group A drugs fluoroquinolones and linezolid. Reliable detection of the most important resistance conferring mutations of group C drugs amikacin and ethambutol could also be achieved.

Summary: LiquidArray MTB-XDR VER1.0 is a powerful tool for reliable detection of resistances related to XDR-TB.