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Extended-spectrum cephalosporins (ESCs) are critically important antimicrobial agents for human and veterinary medicine. ESC resistance (ESC-R) genes have spread worldwide through plasmids and clonal expansion, yet the distribution and dynamics of ESC-R genes in different ecological compartments are poorly understood. Here we use whole genome sequence data of Enterobacterales isolates of human and animal origin from Europe and North America and identify contrasting temporal dynamics. AmpC β-lactamases were initially more dominant in North America in humans and farm animals, only later emerging in Europe. In contrast, specific extended-spectrum β-lactamases (ESBLs) were initially common in animals from Europe and later emerged in North America. This study identifies differences in the relative importance of plasmids and clonal expansion across different compartments for the spread of different ESC-R genes. Understanding the mechanisms of transmission will be critical in the design of interventions to reduce the spread of antimicrobial resistance.

e R esistance to extended-spectrum cephalosporins (ESC) has rarely been detected in Enterobacteriaceae from beef cattle in Canada (1); in contrast, in the United States, it has repeatedly been found in bacteria from cattle (see, for instance, references 2 to 5). To assess whether similar bacteria are present in beef cattle in Alberta, Canada, we used enrichment cultures and PCR to increase the sensitivities of our detection methods.Four hundred thirty-two composite fecal samples were collected from 73 pens in four major feedlots in Alberta from May 2014 to April 2015. The samples were grown in EC broth (BD Difco) containing cefotaxime (2 g/ml), and aliquots were plated on MacConkey agar with ceftriaxone (1 g/ml) and then on Trypticase soy agar with ampicillin (32 g/ml). Lactose-fermenting, indole-positive isolates were investigated further. The remaining enrichment cultures were centrifuged, and the sediment was used for DNA extractions using a QIAamp DNA minikit. Real-time PCR with custom TaqMan primer/probe combinations for the bla CTX-M-1 , bla CTX-M-2 , bla CTX-M-8 , bla CTM-X-9 , bla CTX-M-25 , bla CMY , bla SHV , and bla TEM gene groups were performed using these extracts. Mock extractions and no-template controls were run with every batch to control for nonspecific background signals. A multivariate probit analysis was conducted to assess dependencies among the gene groups under consideration and their associations with season, feedlot, and pen. Sequencing of PCR products was used to identify gene variants in a subset of samples and isolates (http://www.lahey.org/Studies/).The PCR results from the enrichment cultures (Table 1) demonstrate that ESC resistance genes are widespread in feces from beef cattle in Alberta. Testing isolates from a subsample of these cultures confirmed the accuracy of these results (53/59 isolates were positive for one or two of these gene groups). Genes of the TEM group were almost exclusively (n ϭ 234; 96%) found together with genes of the other groups (Table 1) and were likely not extended-spectrum ␤-lactamases. The following ␤-lactamase genes (and numbers of samples [n ϭ 29]) were found in the indicated groups: TEM group, bla TEM-1 (4 [all 4 were from samples positive for one or several of the other ␤-lactamase groups]); SHV group, bla SHV-2a (2); CMY group, bla CMY-2 (2); CTX-M-1 group, bla CTX-M-15 (2), bla (1), bla CTX-M-55 (8), bla CTX-M-61 (1), and bla (1 [GenBank accession number KT251041]); CTX-M-2 group, bla CTX-M-2 (1) and bla CTX-M-115 (2); and CTX-M-9 group, bla CTX-M-24 (1), bla CTX-M-27 (2), and bla CTX-M-65 (2). Although more positive samples were detected in the summer, the

The goal of this study was to determine the frequency of resistance to extended-spectrum cephalosporins (ESCs) in Escherichia coli and other Enterobacterales from turkeys in Canada and characterize the associated resistance determinants. Pooled fecal samples were collected in 77 turkey farms across British Columbia, Québec, and Ontario. Isolates were obtained with and without selective enrichment cultures and compared to isolates from diagnostic submissions of suspected colibacillosis cases in Ontario. Isolates were identified using MALDI-TOF and susceptibility to ESCs was assessed by disk diffusion. The presence of bla CMY , bla CTX-M , bla TEM, and bla SHV was tested by PCR. Transformation experiments were used to characterize bla CMY plasmids. Genome sequencing with short and long reads was performed on a representative sample of bla CTX-M -positive isolates to assess isolates relatedness and characterize bla CTX-M plasmids. For the positive enrichment cultures (67% of total samples), 93% (587/610) were identified as E . coli , with only a few other Enterobacterales species identified. The frequency of ESC resistance was low in E . coli isolates from diagnostic submission (4%) and fecal samples without selective enrichment (5%). Of the ESC-resistant Enterobacterales isolates from selective enrichments, 71%, 18%, 14%, and 8% were positive for bla CMY , bla TEM, bla CTX-M, and bla SHV , respectively. IncI1 followed by IncK were the main incompatibility groups identified for bla CMY plasmids. The bla CTX-M-1 gene was found repeatedly on IncI1 plasmids of the pMLST type 3, while bla CTX-M-15 , bla CTX-M-55 , and bla CTX-M-65 were associated with a variety of IncF plasmids. Clonal spread of strains carrying bla CTX-M genes between turkey farms was observed, as well as the presence of an epidemic bla CTX-M-1 plasmid in unrelated E . coli strains. In conclusion, Enterobacterales resistant to ESCs were still widespread at low concentration in turkey feces two years after the cessation of ceftiofur use. Although bla CMY-2 is the main ESC resistance determinant in E . co...