Antimicrobial-resistant Escherichia coli isolated from canine urine in Saskatchewan (2018 to 2022)

Antimicrobial resistance (AMR) is a serious threat to human and animal health; the emergence of 3rd-generation cephalosporin- and fluoroquinolone-resistant Enterobacterales is particularly problematic. Because Escherichia coli is the most common cause of urinary tract infections in dogs, AMR has real-world impact. The objectives of this study were to evaluate the antimicrobial susceptibility of canine urinary isolates of E. coli and to determine if AMR is increasing in Saskatchewan.

A total of 576 diagnostic isolates of canine urinary E. coli from individual dogs were grown by Prairie Diagnostic Services (Saskatoon, Saskatchewan). Antimicrobial minimum inhibitory concentrations (MICs) were determined via broth microdilution and agar dilution. Strains of E. coli resistant to the β-lactams and nalidixic acid were screened for broad-spectrum β-lactamases and plasmid-mediated quinolone resistance genes via PCR. Changes in the annual frequency of resistance and median MIC were evaluated using generalized linear models.

Most (76.9%) isolates were pan-susceptible, whereas only 4.3% were multidrug resistant. Ampicillin resistance was most common (13.9%), though resistance to other agents occurred infrequently (≤ 10%). Only 2.7% and 1.2% of isolates possessed CMY-2- or CTX-M-type β-lactamases, respectively. Plasmid-mediated quinolone resistance genes were present in < 1% of isolates. Although the frequency of categorical resistance did not rise significantly, the median annual ampicillin, nalidixic acid, and chloramphenicol MICs increased significantly.

Antimicrobial resistance among canine urinary E. coli is not yet common in our region. The findings support the continued use of 1st-line therapies recommended by the International Society for Companion Animal Infectious Diseases.