Shiga Toxin-Producing Escherichia coli in Animal Reservoirs, Serotype Diversity, Virulence Profiles, and Antimicrobial Resistance Trends (2020-2026): A Scoping Review.

Background/Objectives: Shiga toxin-producing Escherichia coli (STEC) are important zoonotic pathogens associated with gastrointestinal infections and hemolytic-uremic syndrome (HUS). Increasing serotype diversity, emergence of hybrid strains, and growing antimicrobial resistance complicate surveillance and treatment. This review summarizes recent data on STEC isolated from major animal reservoirs between 2020 and 2026. Methods: We comparatively analyzed peer-reviewed, open-access studies investigating STEC from cattle, sheep, goats, poultry, wildlife, and related animal products. We extracted and evaluated data on serotypes, virulence genes, hybrid pathotypes, and antimicrobial resistance determinants. Results: High serotype diversity was observed across all reservoirs, with non-O157 STEC frequently predominating over O157:H7. Ruminant isolates commonly carried stx2 and additional virulence determinants associated with severe human disease, confirming cattle and small ruminants as major reservoirs of highly pathogenic STEC. Poultry-associated isolates showed greater variability in virulence profiles but frequently exhibited high rates of multidrug resistance. Hybrid strains combining virulence traits characteristic of multiple E. coli pathotypes were increasingly reported. Livestock-associated STEC commonly carried resistance determinants against β-lactams, tetracyclines, sulfonamides, quinolones, and polymyxins, whereas wildlife isolates generally showed lower rates of resistance. Conclusions: Animal-associated STEC populations demonstrate increasing genomic diversity, pathogenic potential, and antimicrobial resistance. The growing prevalence of non-O157 and hybrid strains highlights the limitations of traditional serotype-focused surveillance and emphasizes the need for integrated One Health monitoring strategies.