Evaluation of methods for testing the susceptibility of clinical Mycobacterium tuberculosis isolates to pyrazinamide.

Pyrazinamide (PZA) is a first-line antituberculosis (anti-TB) drug capable of killing nonreplicating, persistent Mycobacterium tuberculosis. However, reliable testing of the susceptibility of M. tuberculosis to PZA is challenging. Using 432 clinical M. tuberculosis isolates, we compared the performances of five methods for the determination of M. tuberculosis susceptibility to PZA: the MGIT 960 system, the molecular drug susceptibility test (mDST), the pyrazinamidase (PZase) activity assay, the resazurin microtiter assay (REMA), and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction test. The sensitivities of the MGIT 960 system, the PZase activity assay, the mDST, the REMA, and the MTT assay were 98.8%, 88.8%, 90.5%, 98.8%, and 98.2%, respectively. The sensitivities of the PZase activity assay and the mDST were lower than those of the other three methods (P < 0.05). The specificities of the MGIT 960 system, the PZase activity assay, the mDST, the REMA and the MTT assays were 99.2%, 98.9%, 90.9%, 98.5%, and 100%, respectively. The specificity of the mDST was lower than those of the other four methods (P < 0.05). In conclusion, the MGIT 960 system, the MTT assay, and the REMA are superior to the PZase activity assay and the mDST in determining the susceptibility of M. tuberculosis to PZA. The MTT assay and the REMA might serve as alternative methods for clinical laboratories without access to the MGIT 960 system. For rapid testing in well-equipped laboratories, the mDST might be the best choice, particularly for small quantities of M. tuberculosis. The PZase activity assay has no obvious advantage in the assessment of M. tuberculosis susceptibility to PZA, as it is less accurate and requires larger quantities of bacteria.