Diversity of CTX-M-positive Escherichia coli recovered from animals in Canada.

Historically, extended-spectrum cephalosporin resistance in bacteria from animals in Canada has been attributed to the SHV and CMY β-lactamase families. This pattern is beginning to change with the emergence of the blaCTX-M gene family among Escherichia coli recovered from various animal species. Here we analyze and compare whole genome sequences of blaCTX-M-positive E. coli isolates (n = 173) from dogs, chicken, swine, horses and beef cattle in Canada. Ten blaCTX-M variants were identified with blaCTX-M-1,-14, -15, -27 and blaCTX-M-55 being identified in most animal species. These variants occurred across many sequence types, suggesting that mobile genetic elements mediate the spread of blaCTX-M. The variants blaCTX-M-14, -15, -27 and blaCTX-M-55 are associated with the global spread of blaCTX-M in human clinical isolates and their presence could be indicative of transfer between humans and animals. These variants were also the principal variants identified among sequence type 131 isolates, which were not associated with any other species than dogs. These isolates carried the same blaCTX-M variants as E. coli isolates found in humans. Close contact may promote the transmission of these isolates between humans and companion animals.