Characteristics of pncA gene in multidrug-resistant Mycobacterium tuberculosis isolates and its correlation with drug resistance to pyrazinamide

Abstract

To understand the characteristics of pncA gene in multidrug-resistant Mycobacterium tuberculosis isolates and its correlation with drug resistance to pyrazinamide. A total of 127 clinical isolates of multidrug-resistant mycobacterium tuberculosis were collected from Shenzhen from year 2007 to 2009. PZA susceptibility was determined by the BACTEC MGIT 960 PZA method. Pyrazinamidase (PZase) activity testing and pncA gene sequencing were performed in all the isolates. The type and frequency of mutations in pncA were determined. Correlation analysis among PZA susceptibility and PZase activity, pncA mutation was performed. Among the 127 isolates, 62 isolates (48.8%) were found resistance to PZA. Among the 62 PZA resistant isolates, 45 isolates which had various pncA mutations were negative for PZase. Mutation rate was 77.4% (48/62) in total PZA resistance isolates. Different types of 48 resistant isolates were identified in the pncA gene, including base substitution (33 isolates), frame shift mutation (12 isolates) and codon mutation (3 isolates). No mutations except one isolate (N11D) existed in all PZA-susceptibility isolates which were positive for PZase. A total of 5 mutations which have not been described previously were found as follows: H57P, P62Q, G108R, D110Y and G162V. The correlation among the PZA susceptibility and the PZase activity (r = 0.895, P < 0.05), the pncA mutation (r = 0.779, P < 0.05) were significant in 127 multidrug-resistant isolates. A high diversity of pncA gene mutation was found among PZA resistant strains of MTB. This study revealed five new mutations of the pncA gene that were not previously described, which scattered in the hot-spot regions located in the metal coordination site and active site of the enzyme. Mutations had a high correlation with the PZA resistance.