Source
Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association, Tokyo, Japan.
Abstract
OBJECTIVE:
To characterize the correlation of the mutations in the pncA gene encoding pyrazinamidase (PZase) of Mycobacterium tuberculosis to a loss of PZase activity and development of pyrazinamide (PZA) resistance.
DESIGN:
The association of PZase activity, minimum inhibitory concentrations (MICs), and mutations in the pncA gene of M. tuberculosis isolated in mostly Asian countries was investigated.
RESULTS:
One hundred thirty-five out of 168 isolates were PZase positive, and 33 were negative. The MICs of PZA at pH 6.0 were over 400 micrograms/ml for all 33 PZase-negative isolates, while those of PZase-positive isolates were equal to or less than 200 micrograms/ml. Among 33 PZase-negative isolates sequenced, 32 (97%) had mutations within the pncA gene. A mutation was seen in various regions throughout the pncA gene. It was surprising that all three strains of in vitro selected PZA resistant mutants were PZase-positive and showed no change in the pncA gene. These results indicate that additional mechanisms may be involved in PZA resistance. No mutations were observed in all of 135 PZase-positive M. tuberculosis isolates tested, indicating that mutations in the pncA gene could be involved in the loss of PZase activity.
CONCLUSIONS:
Sequencing analysis of the pncA gene should provide rapid diagnosis of PZA resistant clinical isolates of M. tuberculosis.