Abstract Aims: Present study was aimed to determine ESBL-encoding genes distribution in Diarrhoeagenic Escherichia coli (DEC) isolated from animalsource food products and human clinical samples in Mashhad, Iran. The strains were also further studied to analyse genotypic diversity and find genetic relationships between them. Methods and Results: The number of 85 DEC strains including 52 and 33 strains isolated from 300 food and 520 human stool samples, respectively. Randomly amplified polymorphic DNA (RAPD), and repetitive extragenic palindromic-PCR (rep-PCR) typing methods were used to track their genetic relationships. The ESBL-encoding genes prevalence was approximately 70% in both groups of isolates. The blaTEM, blaCTX-M and blaSHV were prevalent in 671, 20 and 106% of isolates, respectively. The ESBL-positives showed significantly higher resistance rates to gentamicin, co-trimoxazole, tetracycline, aztreonam and chloramphenicol (P < 005). Fingerprinting patterns-based dendrograms divided DEC strains into separate clusters irrespective of their sources and pathotypes. In typing field, rep-PCR provided more discriminatory power (Simpson’s index of diversity (SID) = 0925) than RAPD (SID = 0812). Conclusion: Molecular similarity between certain animal-sourced food products and clinical sample strains supported food-borne transmission routes for genotypic elements such as ESBL-encoding genes. Significance and Impact of the Study: Findings emphasize the importance of resistance issues, the need to improve treatment guidelines and routine surveillance of hygienic measures during food processing.

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