Genetic and phenotypic characterization of pyrazinamide-resistant mycobacterium tuberculosis complex isolates in Japan.

The pncA gene mutations associated with pyrazinamide (PZA) resistance in Mycobacterium tuberculosis complex were determined in 26 PZA-resistant isolates in Japan. Of the 26 PZA-resistant isolates included, 21 were negative for pyrazinamidase (PZase). Of these, 20 isolates had various pncA mutations, resulting in alteration of primary amino acid sequence. However, 1 PZase-negative isolate did not have any mutation on pncA gene. The remaining 5 PZA-resistant isolates were positive for PZase and had identical pncA alleles with PZA-susceptible isolates. IS6110 RFLP analysis demonstrated various distinct IS6110 types and 5 pairs of isolates were very close to each other (>90% identical pattern). This study demonstrates that most of the PZA resistance is a result of various mutations on pncA resulting in loss of PZase activity. Further investigation, particularly on PZase-positive but PZA-resistant isolates and a PZase-negative isolate with no mutation on pncA, should be urgently done.