Phenotypic and Molecular Characterization of Escherichia coli O157:H7 Isolates from Dogs (Canis lupus familiaris)

This study aimed to detect and characterise phenotypically and molecularly Escherichia coli O157:H7 isolates of canine origin (Canis lupus familiaris). Initially, a bank of 122 E. coli strains was screened for the O157:H7 serotype, yielding 4 positive samples. Among the total strain bank, the virulence genes eaeA and hlyA were detected in 5.74% (7/122) and 0.82% (2/122) of isolates, respectively, while stx1 and stx2 were not found. To further investigate horizontal gene, transfer and resistance profiles, transconjugation experiments were performed using the O157:H7-positive isolates, resulting in nine transconjugants. PCR analysis of the transconjugants revealed the presence of eaeA (88.88%), hlyA (44.44%), and resistance genes such as blaTEM (77.77%), blaCTX-M (88.88%), and tetA (22.22%). Disk diffusion (Kirby-Bauer) assays confirmed that 88.88% of isolates were phenotypically resistant to ESBL and AmpC antibiotics. Resistance to specific antimicrobials included cefotaxime (55.55%), ciprofloxacin (22.22%), enrofloxacin (33.33%), and sulfamethoxazole/trimethoprim (44.44%). Notably, resistance to ampicillin, vancomycin, and erythromycin was observed in 88.88% of isolates. This study highlights the significant prevalence of multi-drug resistant E. coli O157:H7 and the potential for plasmid-mediated gene transfer in canine populations in central Ecuador, raising important concerns for public health.