Genetic Diversity, Antimicrobial Resistance, and Biofilm-Forming Potential of Equine Fecal Escherichia coli in Northern Iran

This study was carried out to examine the biofilm-forming ability, antimicrobial resistance, frequency of biofilm, and resistance genes, as well as the phylogenic grouping of Escherichia coli isolates originating from equine samples. In total, 157 E. coli strains were isolated from fresh feces samples of healthy horses in northern Iran. The samples were examined in terms of biofilm formation and antimicrobial susceptibility using a microtiter plate and disc-diffusion test, respectively. PCR amplification was adopted to find the genes that confer biofilm formation and resistance to β-lactam, chloramphenicol, tetracyclines, aminoglycosides, quinolones, sulfamethoxazole, and trimethoprim, and for phylogenetic analysis. More than 50% of isolates showed MDR phenotype. The most significant level of resistance was detected for streptomycin (59.87%), followed by trimethoprim-sulfamethoxazole (29.93%) and oxytetracycline (28.66%). Imipenem and norfloxacin were the most potent antibiotics. Phylogenetic groups B1 (46.50%) and A (21.66%) were the most common groups in isolates, followed by C (6.37%), clade I (5.10%), E (4.46%), D (3.82%), and B2 (2.55%). All isolates in phylogroups B2 and D carried all biofilm-related genes. In addition, antimicrobial resistance genes were common in phylogroups B2, D, A, B1, and E. These findings demonstrate that in northern Iran, healthy horses harbor potential extraintestinal pathogenic and MDR E. coli isolates. These animals can be reservoirs for antibiotics-resistant isolates. The obtained data support the current interest regarding antimicrobial resistance, MDR shedding, and managing the use of antimicrobials in veterinary science.