Introduction

AMR has become a common concern of animal and human health care

professionals. MDR infections increase the morbidity and mortality of patients and result in increased costs to the client and the health care system^49,248. In dogs, the urinary tract has been implicated as the most common extra intestinal site for MDR E. coli²¹. What’s more, the close contact between humans and their pets has implications for the sharing of resistant commensal and pathogenic bacteria between species. While the exact role of dogs in this transmission cycle has not been adequately studied, evidence of “strain sharing” has been demonstrated with Clostridium difficile and MRSA^24–26,28. Similarly, multiple studies have shown support for the sharing of E. coli between dogs and humans through the simultaneous isolation of MDR strains from cohabitating humans and their canine companions in both hospital and home environments^22,23.

Antimicrobials are commonly used in companion animal veterinary practice. One study in the United Kingdom estimated that more than one third of consults with canine patients resulted in the prescription of antimicrobials⁴². Uncomplicated or sporadic UTIs occur in approximately 14% of dogs that visit a veterinarian in their lifetime, representing a frequent reason for the prescription of antimicrobials⁵³. Similar to the case in humans, the Gram-negative bacterium E. coli is the most frequent pathogen in UTI cases,

accounting for upwards of 50% of positive canine urine cultures52,56,68,249. According to ISCAID, empirical treatment options include members of the -lactam class; such as amoxicillin, or the potentiated sulfonamide, SXT^50,54,58. Alternative therapies with a broader spectrum of activity, such as fluoroquinolones (enrofloxacin, ciprofloxacin), chloramphenicol, doxycycline, fosfomycin and nitrofurantoin should be reserved for

cases where laboratory results indicate a lack of susceptibility to empirical treatments.

In general, it is considered unnecessary to prescribe these agents in cases of uncomplicated cystitis given their relative importance in treating human infections, coupled with the increasing frequency of resistance⁵⁴.

From a clinical perspective, the most troubling resistance mechanism in canine urinary E. coli, include ESBLs, Class C (AmpC) β-lactamases, and PMQR genes¹⁰³. ESBLs are capable of hydrolyzing even those extended-spectrum -lactams that had been modified to confer resistance to the first-generation enzymes. The first ESBL identified in an animal was isolated from the feces of a healthy laboratory dog in

Japan²⁵⁰. In general, SHV, TEM and CTX-M type ESBLs are among the most common, however since the beginning of the 21^st century, CTX-M type enzymes have become most prevalent^76,110,117. Currently, the most widely distributed CTX-M alleles are CTX-M-1, -15 and -14, having been isolated from both healthy and diseased companion

animals¹⁰³. While CTX-M-1 and CTX-M-15 predominate in Europe, in North America, CTX-M-15 is most commonly encountered, particularly among companion animals suffering from cystitis29,127,128,135,138,216,251–257. In Asia CTX-M-14 is the dominant enzyme type, however, additional ESBLs, including SHV-12 have been identified in companion animals in Spain, Germany, China and the U.S.136,253,255,258. AmpC -lactamases confer resistance to cephamycins (cefoxitin for example) and “classic” -lactamase inhibitors, in addition to ESCs. Most often, AmpC -lactamase producing E.coli acquire these enzymes on plasmids¹¹⁹. CMY-2 is the most common type detected in companion animals, having been identified in dogs from Japan, Denmark and Canada^120–122. Fluoroquinolones are a broad-spectrum antimicrobial class that exert their mechanism

of action by interfering with DNA replication⁴⁹. Originally, acquired resistance to fluoroquinolones was thought to occur strictly through chromosomal mutation in the genes gyrA and parC that encode the drug target^45,131. However, the first report of PMQR occurred in the late 1990s¹³². To date, three types of transmissible quinolone resistance genes have been reported. The target protecting proteins (qnrA, qnrB, qnrC, qnrD and qnrS); the inactivating enzyme aac(6′)- Ib-cr, and the efflux pumps qepA and oqxAB⁴⁵. In companion animals the gene aac(6′)- Ib-cr appears to be the most

widespread, having been identified in E. coli from both healthy and diseased companion animals across Europe, Australia, Asia and the U.S.135–139,142,143. The tendency of the aac(6′)- Ib-cr gene to co-locate on plasmids harbouring ESBLs is of particular concern, as it provides the framework for the emergence of MDR. In Canada, the efflux pump QepA and the Aac(6′)-Ib-cr enzyme have been much more commonly reported than the Qnr proteins among urinary E. coli isolated from humans173,175,259. However, we know of no studies documenting either of these PMQR determinants in companion animal E. coli in Canada.

The emergence of transmissible AMR among canine urinary E. coli in other regions warrants an investigation into the prevalence and mechanisms of resistance in this pathogen population in Canada. In fact, various consensus statements in veterinary medicine call for more prudent use of antimicrobials by veterinarians and identify urinary E. coli as an important target for surveillance studies^15,49,50. Unfortunately, national surveillance programs in Canada do not address AMR in companion animals, focusing instead on food animal pathogens with the potential for foodborne transmission¹.

Where surveillance literature exists for canine uropathogens, the results indicate significant geographic variation in the frequency of resistance. For example, resistance is more prevalent in Asian and African countries, compared to Canada and northern European countries such as Sweden122,205,212,221–224. Previous work out of

Saskatchewan detected a particularly low frequency of resistance (~80% pan

susceptibility) among canine urinary E. coli¹²². These baseline findings provide a unique opportunity to detect the emergence of clinically relevant resistance determinates in this region. This study aims to describe the frequency and mechanisms of AMR among E.

coli causing canine UTIs in Western Canada during a four-year surveillance period.