Abstract
Background: Diarrheagenic Escherichia coli (DEC) represents a major cause of enteric disease in cattle worldwide and poses significant zoonotic and food-safety risks. Objectives: This study aimed to determine the prevalence of DEC in animal and environmental samples from dairy and beef cattle farms, characterize recovered isolates serologically and by virulence genotyping, and assess their antimicrobial resistance (AMR) profiles.
Materials and Methods: A total of 150 animal rectal swabs (93 from dairy cattle and 57 from beef cattle) and 240 environmental samples (152 from dairy and 88 from beef farms) were collected. Isolates were identified biochemically and serologically, confirmed by PCR for virulence genes (stx1, stx2, STa, LT), and subjected to disk-diffusion susceptibility testing against 16 antimicrobials.
Results: The overall DEC prevalence was 24.7% in dairy cattle and 28.1% in beef cattle. Calves exhibited the highest positivity rates (34.2% and 33.3%, respectively). Environmental contamination rates reached 13.8% and 17.0% in dairy and beef farms. Bedding material was the most contaminated environmental source. Among 30 food-product isolates characterized, seven serogroups were identified; O145 (23.3%, EAEC) and O45 (20.0%, STEC) predominated. PCR revealed stx1 (63.3%), stx2 (60.0%), STa (26.7%), and LT (23.3%) among isolates. AMR profiling demonstrated extremely high resistance to cefadroxil (100%), amoxicillin/clavulanate (93.3%), and cephalexin (93.3%), and nearly universal resistance to oxytetracycline (90.0%). Significant inter-drug variation was documented by chi-square analysis.
Conclusion: The widespread prevalence of multidrug-resistant DEC in Egyptian cattle farms, coupled with detection of virulent serogroups in environmental samples, underscores critical public-health and food-safety implications. Urgent antimicrobial stewardship and enhanced farm biosecurity measures are warranted.

Key words: diarrheagenic E. coli; cattle; serotyping; virulence genes; antimicrobial resistance