Purpose: The objectives of this study were to compare strains of varying intimin and flagellar composition from each of these seven serogroups for adherence and attaching-effacing (A/E) lesions in bovine and human colonic mucosal epithelial cells.
Methods: Bovine colonic mucosal explants and human Caco-2 cells were inoculated with strains, and adherence and invasion were evaluated by immunohistochemistry (IHC), fluorescent actin staining (FAS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and a standard invasion assay.
Results: Based on IHC, all strains adhered to mucosal epithelium in explants. By SEM, adherent O104:H4 bacteria had structures resembling aggregative adherence fimbria and some, e.g., O45:H2, O103:H2, and O103:[H11] adhered to intestinal mucus and epithelial cells via structures morphologically consistent with flagella. All intimin-positive strains induced A/E lesions on Caco-2 cells by FAS. Invasion in explants was detected by IHC and TEM with one O103:H2 and one O104:[H21] strain, with the O103:H2 strain also invasive in Caco-2 cells. Non-O157 STEC expressing different flagellar types, viz., H2, H10, H11, H16, H19, H21, and H28, and variants of intimin, viz., β1, ε, θ, and γ1, adhered to bovine colonic epithelium and induced the formation of A/E lesions. Non-O157 STEC strains lacking intimin were also shown to adhere to bovine colonic epithelium; hence, must utilize other mechanisms for attachment.
Significance: These studies suggest that most non-O157 STEC adulterant strains and potentially O104:H4 have the capacity to colonize bovine intestinal epithelium. More studies are needed to address these adherence and colonization mechanisms to provide a basis for effective pre-harvest interventions.