Virulence and Antibiotic Resistance of aEPEC/STEC Pathotypes with Serotype Links to 16 Isolated from Irrigation Water.

Irrigation water can serve as a reservoir and transmission route for pathogenic , posing a threat to food safety and public health. This study builds upon a previous survey conducted in Hermosillo, Sonora (Mexico), where 445 samples were collected from a local Honeydew melon farm and associated packing facilities. Among the 32 strains recovered, two strains, A34 and A51, were isolated from irrigation water and selected for further molecular characterization by PCR, due to their high pathogenic potential. Both strains were identified as hybrid aEPEC/STEC pathotypes carrying and virulence genes. Adhesion assays in HeLa cells revealed aggregative and diffuse patterns, suggesting enhanced colonization capacity. Phylogenetic analysis classified A34 within group B2 as associated with extraintestinal pathogenicity and antimicrobial resistance, while A51 was unassigned to any known phylogroup. Serotyping revealed somatic antigens shared with 16, suggesting possible horizontal gene transfer or antigenic convergence. Antibiotic susceptibility testing showed resistance to multiple β-lactam antibiotics, including cephalosporins, linked to the presence of and . Although no plasmid-mediated quinolone resistance genes were detected, resistance may involve efflux pumps or mutations in and . These findings are consistent with previous reports of adaptability in agricultural environments, suggesting potential genetic adaptability. While our data support the presence of virulence and resistance markers, further studies would be required to demonstrate mechanisms such as horizontal gene transfer or adaptive evolution.