Escherichia coli O157:H7-secreted cytotoxins are toxic to enterocytes and increase Escherichia coli O157:H7 colonization of jejunum and descending colon in cattle

Enterohemorrhagic Escherichia coli (EHEC) O157:H7-secreted cytotoxins are toxic to target cells and enhance colonization of intestinal tissues in disease-susceptible animals. It is unclear what role, if any, EHEC O157:H7-secreted cytotoxins play in the colonization of intestinal tissues of healthy reservoir animals. We previously reported that EHEC O157:H7 colonization sites were associated with focal hemorrhages in the jejunum and descending colon of persistent shedding cattle, suggesting a potential role for cytotoxins in EHEC O157:H7 colonization. We have used a traditional EHEC O157:H7 IVOC adherence assay and a novel lawn assay to examine the role of EHEC O157:H7-secreted cytotoxins in EHEC O157:H7 strain colonization of the jejunum and descending colon of non-persistent and persistent shedding cattle. Four EHEC O157:H7 strains that were previously reported to differentially colonize cattle produced cytotoxins that were differentially active against epithelial cells from the jejunum and descending colon. There was a relationship between EHEC O157:H7-secreted cytotoxin activity and strain adherence for epithelial cells from the jejunum and descending colon of cattle. There was also a greater susceptibility of epithelial cells from the jejunum and descending colon to EHEC O157:H7-secreted cytotoxins of persistent shedding cattle compared with non-persistent shedding cattle. Addition of the most active secreted cytotoxins from EHEC O157:H7 R318N to the IVOC adherence assays significantly increased the adherence of the most (R318N) and least (H4420N) virulent EHEC O157: H7 strain to intestinal tissues. The current study supports a role for EHEC O157:H7-secreted cytotoxins in enhancing EHEC O157:H7 colonization of intestinal tissues of cattle.