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. The aim of this study was to investigate the antimicrobial susceptibility and ESBL-type of 204 strains of CTX-M-type ESBLs-producing E. coli isolated from 2011 to 2017 in the Chubu region of Japan. Minimal inhibitory concentrations were determined in accordance with the guidelines of the Clinical and Laboratory Standards Institute. Genes encoding CTX-M group β-lactamases were detected by PCR amplification. The CTX-M subtypes were determined using sequence analysis. The CTX-M-9 group was the most frequently detected ESBL group, and CTX-M-27 was the most frequently detected ESBL gene. CTX-M-15-producing strains showed significantly lower rates of susceptibility to tazobactam/piperacillin (TAZ/PIPC) than those by CTX-M-14 and -27-producing strains. Additional analysis of secondary β-lactamases revealed that most of the OXA-1-positive strains were CTX-M-15-producing strains (94.7%). These strains displayed significantly lower susceptibility rates to TAZ/PIPC (47.4%), sulbactam/ampicillin (SBT/ABPC) (0.0%), and amikacin (AMK) (73.7%) than those by 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. The CTX-M-15-producing strains showed reduced susceptibility to TAZ/PIPC, SBT/ABPC, and AMK, presumably due to the co-carriage of OXA-1.