2019 Volume 68 Issue 1 Pages 1-6
A total of 268 clinical isolates of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli collected from Ehime Prefectural Central Hospital were subjected to antimicrobial susceptibility tests using the disk diffusion method. The rate of ESBL-producing E. coli with nonsusceptibility to both ceftazidime (CAZ) and aztreonam (AZT) increased over the study period. The performance of blaCTX-M typing using DNA sequencing showed that blaCTX-M-14 was dominant in periods I and II, but levels of blaCTX-M-27 and blaCTX-M-15 significantly increased, in addition to that of blaCTX-M-14, in period III. The rate of blaCTX-M-27-positive or blaCTX-M-15-positive E. coli cells with nonsusceptibility to both CAZ and AZT were higher than that of the blaCTX-M-14-positive E. coli cells. These data suggest that the increase in the number of ESBL-producing E. coli cells with nonsusceptibility to both CAZ and AZT was due to the increase in the number of blaCTX-M-27-positive or blaCTX-M-15-positive E. coli cells. In addition, a D240G amino acid mutation was detected in the blaCTX-M-27-positive and blaCTX-M-15-positive strains, suggesting that this mutation led to the increase in the rate of nonsusceptibility to both CAZ and AZT.
