Characterization of Pyrazinamide Resistance in Consecutive Multidrug-resistant Mycobacterium tuberculosis Isolates in Sweden between 2003 and 2015

Background: The first line anti-tuberculosis drug pyrazinamide (PZA) is important when treating PZA susceptible multidrug-resistant tuberculosis (MDR-TB). Several drug resistance surveys have however reported PZA resistance among a significant proportion of multidrug-resistant (MDR) cases and this undoubtedly highlights the need for accurate and reliable detection of PZA resistance. Unfortunately, the testing of PZA susceptibility is associated with technical difficulties and even though the introduction of pncA sequencing has helped to address this issue, misclassification may still occur. In this study, we determined the prevalence and characteristics of PZA resistance in Swedish MDR-TB strains. Materials and Methods: 153 MDR-TB strains isolated in Sweden between 2003 and 2015 were analyzed for PZA resistance by considering both phenotypic and genotypic data. Results: The phenotypic test showed that 58% of the multidrug-resistant isolates were PZA resistant and the correlation between phenotype and genotype was solid, although a small number of isolates deviate from the expected phenotypic-genotypic pattern. Conclusion: The results indicate that the prevalence of pyrazinamide resistance among Swedish MDR cases is increasing.