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Background  Pyrazinamide (PZA) plays a unique role in the treatment for multidrug-resistant tuberculosis (MDR-TB) in both first- and second-line regimens. The aim of this study was to investigate the prevalence and molecular characterization of PZA resistance among MDR-TB isolates collected in Chongqing municipality.    Methods  A total of 133 MDR-TB isolates were collected from the smear-positive tuberculosis patients who were registered at local TB dispensaries of Chongqing. PZA susceptibility testing was determined with a Bactec MGIT 960 system. In addition, the genes conferring for PZA resistance were screened by DNA sequencing.    Results  Of these 133 MDR-TB isolates, 83 (62.4%) were determined as PZA-resistant by MGIT 960. In addition, streptomycin- (83.1% vs. 56.0%,  P  < 0.01), ofloxacin- (51.8% vs. 18.0%,  P  < 0.01), kanamycin- (22.9% vs. 2.0%,  P  < 0.01), amikacin- (18.1% vs. 2.0%,  P  = 0.01), capromycin-resistance (12.0% vs. 2.0%,  P  = 0.05), were more frequently observed among PZA-resistant isolates compared with PZA-susceptible isolates. Sequence analysis revealed that 73 out of 83 (88.0%) MDR strains harbored a mutation located in the  pncA  gene, including 55 (75.3%, 55/73) of single nucleotide substitutions and 18 (24.7%, 18/73) of frameshift mutation, while no genetic mutation associated with PZA resistance was found in the  rpsA  gene. The  pncA  expression of strains harboring substitution from A to G at position −11 in the promoter region of  pncA  was significantly lower than that of H37Rv ( P  < 0.01).    Conclusions  In conclusion, our data have demonstrated that the analysis of the  pncA  gene rather than  rpsA  gene provides rapid and accurate information regarding PZA susceptibility for MDR-TB isolates in Chongqing. In addition, loss of  pncA  expression caused by promoter mutation confers PZA resistance in MDR-TB isolates.

Prevalence and molecular characterization of pyrazinamide resistance among multidrug-resistant Mycobacterium tuberculosis isolates from Southern China