Abstract
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 blaCMY, blaCTX-M, blaTEM, and blaSHV was tested by PCR. Transformation experiments were used to characterize blaCMY plasmids. Genome sequencing with short and long reads was performed on a representative sample of blaCTX-M-positive isolates to assess isolates relatedness and characterize blaCTX-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 blaCMY, blaTEM, blaCTX-M, and blaSHV, respectively. IncI1 followed by IncK were the main incompatibility groups identified for blaCMY plasmids. The blaCTX-M-1 gene was found repeatedly on IncI1 plasmids of the pMLST type 3, while blaCTX-M-15, blaCTX-M-55, and blaCTX-M-65 were associated with a variety of IncF plasmids. Clonal spread of strains carrying blaCTX-M genes between turkey farms was observed, as well as the presence of an epidemic blaCTX-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 blaCMY-2 is the main ESC resistance determinant in E. coli from Canadian turkeys, blaCTX-M genes also occur which are often carried by multidrug resistance plasmids. Both clonal spread and horizontal gene transfer are involved in parallel in the spread of blaCTX-M genes in Enterobacterales from Canadian turkeys.
Highlights
The World Health Organization (WHO) and the World Organisation for Animal Health (OIE) define extended-spectrum cephalosporins (ESCs) as critically important antimicrobial agents [1, 2]
The frequency of ESC resistance was low in E. coli isolates from diagnostic submission (4%) and fecal samples without selective enrichment (5%)
Three hundred and eight fecal samples were enriched for ESC-resistant Enterobacterales and one or more ESC-resistant isolate was obtained from 67% of them (82% of farms)
Summary
The World Health Organization (WHO) and the World Organisation for Animal Health (OIE) define extended-spectrum cephalosporins (ESCs) as critically important antimicrobial agents [1, 2] One member of this class, ceftiofur, was used routinely in an extra-label manner in Canada for the prevention of colibacillosis in poultry until 2014, when it was voluntarily withdrawn by the industry [3, 4]. CTX-Ms were detected in human and canine clinical isolates in Canada in the early 2000’s [14, 15], they have appeared only recently in Enterobacterales from farm animals in Canada [9, 12] They have spread among bacteria from cattle, chicken, and swine [9, 10, 11, 16, 17]. A variety of CTX-M types have been identified in E. coli from cattle and swine [12, 16] but those from chickens have all been CTX-M-1 and typically located on IncI1 plasmids [9, 10, 16]
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