Verotoxins (VT; or shiga-like toxins - Stx) are major virulence factors and are key determinants in the patho-physiology of EHEC infections in humans. Cattle are the most important asymptomatic reservoir host for EHEC and recently terminal rectum was identified as the principal site of E. coli O157:H7 colonization in cattle. First objective of this research project was to immuno­-phenotypically characterise terminal rectal tissue of cattle. Secondly, to develop and characterise primary rectal epithelial cell culture as an in vitro model to study interaction with EHEC strains. Initial work identified potential contribution of VTs to bacterium-host interactions and this investigation aimed to characterise roles of VT in colonization of bovine intestinal epithelium by EHEC. For this, adherence of a panel of wild-type and mutant (VT- negative) EHEC strains to primary rectal epithelial cells was assessed. Carriage of VT was associated with greater adherence to epithelium as demonstrated by higher capacity to form microcolonies compared to isogenic VT-negative strains. Pre-treatment of cells with VT produced a similar phenotype. VT exhibited further effects on epithelium through reduction of expression and secretion of IL-8, an important epithelial inflammatory mediator. VT therefore do not show classic cytotoxicity for bovine intestinal epithelium but do exert pleiotropic effects on these cells, by modifying epithelial physiology hence enabling EHEC colonisation. The role of flagella in interaction of E. coli O157:H7 with epithelium was also investigated. H7 flagellum was identified as an adhesin, important in initial adherence of E. coli O157:H7 to bovine rectal epithelium.