Antimicrobial susceptibility of E. coli causing urinary tract infections in dogs in Saskatchewan, Canada
Date
2025-03-04
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Masters
Abstract
Background: E. coli is the most common cause of urinary infections in dogs.
Antimicrobials are the primary treatment for these infections. However, the emergence
of antimicrobial resistance globally is resulting in limited therapeutic options available to
veterinarians and physicians. Since 2013, we have conducted a longitudinal passive
surveillance project targeting E. coli causing UTIs in dogs isolated by a regional
diagnostic lab. The objectives of this study were to describe the antimicrobial
susceptibility of E. coli isolates from Oct 2018-Oct 2022 (n = 576) and the frequency of
epidemiologically important resistance genes.
Methodology: Laboratory records were reviewed to ensure that only one isolate per
dog was included. Antimicrobial minimum inhibitory concentrations (MICs) were
determined by broth microdilution and agar dilution. Based on the susceptibility profile,
isolates were screened for broad-spectrum β-lactamases (ESBL and AmpC enzymes)
and plasmid-mediated quinolone resistance determinants (PMQRs) by PCR, amplicons
were then sequenced to identify gene alleles. Isolates possessing these genes were
sequence typed by multi-locus sequence typing (MLST) to identify resistant clones.
Results: Overall, 76.9% of the isolates were pan-susceptible while 4.3% were
multidrug-resistant (resistant to 3 or more drug classes) according to the CLSI
guidelines and the breakpoints for E. coli in urine. Ampicillin resistance, identified in
13.9% of isolates, was the most common. Resistance to amoxicillin-clavulanic acid,
cefazolin, chloramphenicol, nalidixic acid, and tetracycline was identified in between 5
10% of isolates. Fewer than 5% of isolates were resistant to cefoxitin, ceftriaxone,
cefepime, ciprofloxacin, gentamicin, amikacin, tobramycin, or trimethoprim
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sulfamethoxazole. Broad-spectrum β-lactamases were identified among fewer than 5%
of the isolates; the AmpC type enzymes were most common. Three isolates possessed
a PMQR determinant. Two isolates possessed qnrS8 and a single isolate possessed
aac(6’)-lb-cr.
Discussion: Over the 9-year study period, no significant changes in the frequency of
resistance to ampicillin, amoxicillin-clavulanic acid, cefazolin (only a 4 year period),
nalidixic acid, tetracycline, or chloramphenicol were identified. However, significant
increases in the MICs of ampicillin, nalidixic acid, and chloramphenicol were found,
similar trends were not identified for other drugs. Analysis of MICs over time provides
information about any underlying changes that you cannot find by only analyzing
resistance frequencies. This serves as an early warning for a possible step-wise
increase in MIC which does not occur adjacent to the resistance breakpoint.
Conclusions: This study demonstrates that although E. coli causing canine UTIs
remain susceptible in this region, temporal increases in the MICs to some drugs may
indicate the emergence of resistance. These results support the use of first-line
therapies such as amoxicillin or trimethoprim-sulfamethoxazole recommended by the
ISCAID guidelines in Saskatchewan, Canada. Finally, continued surveillance is
warranted to identify emerging resistance trends and guide future empiric therapy.
Description
Keywords
AMR, E. coli, UTI, Dogs, Veterinary, Resistance genes, MICs, Resistance frequencies, surveillance
Citation
Degree
Master of Science (M.Sc.)
Department
Veterinary Microbiology
Program
Veterinary Microbiology