Aims: The primary objective of this study was to analyze antimicrobial resistance (AMR), with a particular focus on β-lactamase genotypes and plasmid replicon types of STEC strains originating from various animal hosts. Methods and Results: A total of 84 STEC strains were isolated from cattle (n=32), sheep/goats (n=26), pigeons (n=20), and wild animals (n=6) between 2010 and 2018 in various regions of Iran. The Kirby-Bauer susceptibility test and multiple polymerase chain reaction (PCR) panels were employed to elucidate the correlation between AMR and plasmid replicon types in STEC isolates. The predominant replicon types were IncFIC and IncFIB in cattle (46.8%), IncFIC in sheep/goats (46.1%), IncA/C in pigeons (90%), and IncP in wild animals (50%). STEC of serogroups O113, O26, and O111 harbored the IncFIB (100%), IncI1 (80%), and IncFIC+IncA/C (100%) plasmids respectively. A remarkable AMR association was found between ciprofloxacin (100%), neomycin (68.7%), and tetracycline (61.7%) resistance with IncFIC; amoxicillin + clavulanic acid (88.8%) and tetracycline (61.7%) with IncA/C; ciprofloxacin (100%) with IncFIB; fosfomycin (85.7%) and sulfamethoxazole + trimethoprim (80%) with IncI1. IncI1 appeared in 83.3%, 50%, and 100% of the isolates harboring blaCTX-M, blaTEM, and blaOXA β-lactamase genes respectively. Conclusions: The emergence of O26/IncI1/blaCTX-M STEC in cattle farms poses a potential risk to public health. Significance and impact of study: The findings presented in this study report the association between STEC plasmid types, AMR phenotypes, and β-lactamase genotypes.

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