Escherichia coli is reported as the most common organism in humans and animals and has been identified as a critical priority bacterium due to antibiotic resistance by World Health Organization (WHO). Multidrug-resistant (MDR) and Extended-Spectrum β-Lactamase (ESBL)-producing E. coli strains have emerged as a significant global health challenge worldwide due to the difficulty in treating related infections. Poultry has been recognized as an important reservoir of E. coli and may play a crucial role in transmitting these strains to humans. The objective of this study was to determine the prevalence of ESBL-producing and MDR E. coli isolated from poultry and to investigate their association with different phylogenetic groups. The current study was conducted on a collection of 100 E. coli isolates from colibacillosis in poultry. Antimicrobial susceptibility testing, ESBL production, and the prevalence of ESBL-mediated genes (blaTEM, blaSHV, blaOXA, and blaCTX-M) were assessed. Phylogenetic groups were analyzed using both the Clermont 2013 and 2019 updated methods. The highest resistance rates were observed against tetracycline (88%), trimethoprim/sulfamethoxazole (86%), and chloramphenicol (70%). The frequencies of ESBL production and MDR were 41% and 70%, respectively. The blaTEM gene was the most prevalent among isolates, with a frequency of 48%. Phylogenetic group analysis assigned E. coli isolates to B1 (23%), D (22%), A (10%), G (11%), F (8%), B2 (5%), and C (4%). Implementing antimicrobial stewardship is crucial because the circulation of ESBL-producing E. coli and MDR isolates poses a significant threat to both human and veterinary medicine. Furthermore, our results revealed a notable prevalence of phylogroup G in poultry, which is the first report of this finding in Iran.

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