A recent preliminary study from our group found that extended-spectrum cephalosporin-resistance determinants can be detected in the majority of composite fecal samples collected from Alberta feedlot cattle. Most notably, blaCTX-M genes were detected in 46.5% of samples. Further isolate characterization identified blaCTX-M-15 and blaCTX-M-27, which are widespread in bacteria from humans. We hypothesized that Escherichia coli of human and beef cattle origins share the same pool of blaCTX-M genes. In this study, we aimed to assess and compare the genomic profiles of a larger collection of blaCTX-M-positive E. coli recovered from fecal composite samples from Canadian beef feedlot cattle and human wastewater through whole-genome sequencing. The variants blaCTX-M-55, blaCTX-M-32, blaCTX-M-27, blaCTX-M-15, and blaCTX-M-14 were found in both urban wastewater and cattle fecal isolates. Core genome multilocus sequence typing showed little similarity between the fecal and wastewater isolates. Thus, if the dissemination of genes between urban wastewater and feedlot cattle occurs, it does not appear to be related to the expansion of specific clonal lineages. Further investigations are warranted to assemble and compare plasmids carrying these genes to better understand the modalities and directionality of transfer.
Keywords: CTX-M; Escherichia coli; beef cattle; extended-spectrum cephalosporin resistance; wastewater; whole-genome sequencing.