Comparison and development of pyrazinamide susceptibility testing methods for tuberculosis in Thailand

Pyrazinamide (PZA) plays a critical role in shortening tuberculosis treatment duration and in treating multi-drug resistant tuberculosis (MDR-TB). The standard phenotypic MGIT PZA susceptibility testing method is imperfect because it is slow and has potential for false resistance. In this study, we evaluated 2 different phenotypic-based methods, quantitative real-time PCR (qPCR) phage assay, and MTT assay, as well as genotypic sequencing. The assay was evaluated on 71 clinical Mycobacterium tuberculosis isolates (37 MGIT PZA susceptible and 34 MGIT PZA resistant) and compared to the MGIT result. Of these methods, the qPCR phage assay yielded an accuracy of 89% versus standard MGIT while MTT yielded 83%. The genotypic sequencing method yielded 90% accuracy. We conclude that any of these faster PZA susceptibility methods perform reasonably well against a MGIT PZA susceptibility standard.