Aim: Companion animals such as dogs and cats are increasingly recognized as potential reservoirs of antimicrobial resistance (AMR) determinants with relevance to both veterinary and human medicine. This study aimed to characterize antimicrobial resistance profiles of Escherichia coli isolated from dogs and cats in 2024 using a combined phenotypic and genomic approach.
Materials and methods: A total of 115 fecal samples collected from 63 dogs and 52 cats from animal shelters were screened for the presence of cephalosporin-resistant Escherichia coli. A total of 65 isolates were obtained and tested for antimicrobial resistance using the broth microdilution method with EUVSEC3 and EUVSEC2 plates (TREK Diagnostic Systems). Results were interpreted according to the EUCAST (European Committee on Antimicrobial Susceptibility Testing) ECOFFs. Whole-genome sequencing (WGS, 2×300 bp, NextSeq platform, Illumina) was performed for selected isolates to identify AMR genes and plasmid replicons.
Results: Phenotypic testing revealed a high level of resistance to critically important antimicrobials. Resistance to third-generation cephalosporins was observed in nearly all isolates (100% for cefotaxime and 98.5% for ceftazidime), while resistance to ampicillin reached 100%. Similar to ampicillin, ciprofloxacin resistance was observed in all isolates. High levels of resistance were also detected for nalidixic acid (92.3%), tetracycline (98.5%), chloramphenicol (95.4%), and gentamicin (90.8%). In contrast, all isolates remained fully susceptible to critically important last-resort antimicrobials, including meropenem, imipenem, colistin, and amikacin. Resistance to tigecycline, trimethoprim and sulfamethoxazole was detected at lower frequencies.
WGS revealed a predominance of E. coli ST457, suggesting clonal dissemination among companion animals. Most isolates carried ESBL genes, primarily blaCTX-M-32, with single isolates harbouring blaCTX-M-15 or blaCTX-M-55. The IncF replicons (IncFIA/IncFIB) were common.
Conclusions: Dogs and cats may serve as an important reservoir of multidrug-resistant and ESBL-producing E. coli, highlighting the need for AMR surveillance in companion animals within a One Health framework.
