Distribution and Antimicrobial Susceptibility Pattern of CTX-M-type Extended-Spectrum β-Lactamase-Producing Escherichia coli Isolated in Chubu Region, Japan.

The widespread prevalence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli limits treatment options and is a worldwide problem. This study aimed to investigate the antimicrobial susceptibility and ESBL types of 204 strains of CTX-M-type ESBLsproducing E. coli isolated from 2011 to 2017 in the Chubu region of Japan and to identify factors correlated with susceptibility. Minimal inhibitory concentrations were determined in accordance with the guidelines of the Clinical and Laboratory Standards Institute. Genes encoding β-lactamases were detected by PCR amplification. The CTX-M subtypes were determined using sequence analyses. CTX- M-15-producing strains showed significantly lower susceptibility rates to tazobactam/piperacillin (TAZ/ PIPC) than CTX-M-14 and -27-producing strains. Additional analyses of secondary β-lactamases revealed that most of the OXA-1-positive strains were CTX-M-15-producing strains (94.7%). The OXA-1-positive strains displayed significantly lower susceptibility to TAZ/PIPC (47.4%), sulbactam/ ampicillin (0.0%), and amikacin (73.7%) than the OXA-1-negative strains, suggesting that the high non-susceptibility rate of the CTX-M-15-producing strain was due to the co-carriage of OXA-1. Statistical analyses showed that OXA-1-positive strains were present in significant amounts in patients aged ≥65 years, suggesting that older patients have a higher risk of being refractory to treatment.