Dramatic rise in the proportion of ESBL-producing Escherichia coli and Klebsiella pneumoniae among clinical isolates identified in Canadian hospital laboratories from 2007 to 2016.

Objectives: To assess the prevalence, antimicrobial susceptibilities and molecular characteristics of ESBL-producing Escherichia coli and Klebsiella pneumoniae infecting patients receiving care in Canadian hospitals from January 2007 to December 2016. Methods: Clinical isolates of E. coli (n=8387) and K. pneumoniae (n=2623) submitted to CANWARD, an ongoing Canadian national surveillance study, were tested using the CLSI reference broth microdilution method to determine their susceptibility to 15 antimicrobial agents. ESBL-producing E. coli and K. pneumoniae confirmed by the CLSI phenotypic method and putative AmpC-producing E. coli underwent PCR testing and DNA sequencing to identify resistance genes. Annual proportions of isolates harbouring ESBL and AmpC genes were assessed by the Cochran-Armitage test of trend. Results: The annual proportion of isolates of E. coli that were ESBL producing increased from 3.4% in 2007 to 11.1% in 2016 (P<0.0001); >95% of ESBL-producing E. coli were susceptible to amikacin, colistin, ertapenem, meropenem and tigecycline. The proportion of isolates of K. pneumoniae that were ESBL producing increased from 1.3% in 2007 to 9.7% in 2016 (P<0.0001); >95% of ESBL-producing K. pneumoniae were susceptible to amikacin and meropenem. CTX-M-15 was the predominant genotype in both ESBL-producing E. coli (64.2% of isolates) and ESBL-producing K. pneumoniae (51.0%). The annual proportion of isolates of E. coli that were AmpC producing [annual proportion mean 1.9% (range 0.3%-3.1%)] was unchanged from 2007 to 2016 (P>0.5). Conclusions: The prevalence of both ESBL-producing E. coli and K. pneumoniae increased significantly in Canada during the study period while the prevalence of AmpC-producing E. coli remained low and stable.