Evaluation of the BACTEC MGIT 960 system and the resazurin microtiter assay for susceptibility testing of Mycobacterium tuberculosis to second-line drugs

•The BACTEC MGIT 960 system yielded results more rapid than the REMA.•The BACTEC MGIT 960 showed 100% of reproducibility for all second-line drugs tested.•BACTEC MGIT 960 detected 10 extensively drug-resistant TB cases missed by REMA.•The BACTEC MGIT 960 showed 100% of proficiency for second-line drugs.

Drug resistance in tuberculosis is a major threat to public health and control of the disease worldwide. Given the need of a rapid and accurate detection of Mycobacterium tuberculosis resistance to second-line drugs, this study evaluated the performance of the BACTEC MGIT 960 for second-line, drug susceptibility testing in comparison with the resazurin microtiter assay (REMA), in order to implement the automated methodology in the diagnostic routine of a reference laboratory. Drug susceptibility testing (DST) for second-line drugs of 151 MDR M. tuberculosis clinical isolates was performed by both BACTEC MGIT 960 and REMA, and a panel of 26 M. tuberculosis reference isolates from a proficiency test was tested by the BACTEC MGIT 960. DST for second-line drugs by the BACTEC MGIT 960 system was more rapid, highly reproducible and showed 100% of proficiency. After these results, this methodology was successfully implemented in our diagnostic routine for all MDR-TB patients.