Mutation in pncA is a major mechanism of pyrazinamide resistance in Mycobacterium tuberculosis.
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.


METHODS
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.
Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association, Tokyo, Japan.
K
K
Hirano
M
M
Takahashi
Y
Y
Kazumi
Y
Y
Fukasawa
C
C
Abe
D000581:Amidohydrolases / Q000235:genetics*; D004352:Drug Resistance, Microbial / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000201:enzymology / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011718:Pyrazinamide
D011718:Pyrazinamide; D000581:Amidohydrolases; C022490:pyrazinamide deamidase