Surveillance of Extended-Spectrum Cephalosporin- and Carbapenem-Resistance in Escherichia coli from the Greater Toronto Area, Ontario, Canada.

摘要

The purpose of this study was to investigate the prevalence and mechanisms of extended-spectrum cephalosporin- (ESC) and carbapenem-resistance in Escherichia coli from the GTA. A total of 526 non-duplicate E. coli clinical isolates were collected during March 1-5, 2010 from 13 participant hospitals. Among these, 71 isolates showed reduced susceptibility (rS, intermediate, and/or resistant phenotype) to cefoxitin (FOX) and/or ESC. No carbapenem resistance was detected. Extended-spectrum beta-lactamase genes detected (n=37; 52.1%) belong to the CTX-M-family, including blaCTX-M-15 (78.4%), blaCTX-M-23 (2.7%), blaCTX-M-14 (18.9%). The only plasmid-mediated ampC gene identified among FOXrS isolates (n=49; 69%) was blaCMY-2 (n=7; 14.3%). Seventeen strains (24%) were negative for all beta-lactamase genes tested. Analysis of the chromosomal ampC promoter revealed mutations associated with AmpC hyperproduction. Other mechanisms of resistance (e.g. impermeability and/or unidentified beta-lactamases) cannot be discarded. The most prevalent clone detected was ST131. IncFIA, FIB and Frep were the most common plasmid replicon types detected.