Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2000
Publication Date: N/A
Interpretive Summary: Cattle are an important reservoir of Shiga toxin-producing Escherichia coli (STEC) O157:H7, foodborne pathogens that cause bloody diarrhea and hemolytic uremic syndrome in humans. Experimental infection with O157:H7 causes dysentery and severe enterocolitis in newborn calves, but calves become resistant to clinical disease and infection by 3 wks of age. We hypothesized that age-related differences in binding sites (receptors) for Shiga toxin (Stx) may explain why STEC infection causes clinical disease in newborn, but not older, calves. We compared where Stx bound when it was overlaid on tissue sections from newborn and adult cattle and found similar binding patterns in both ages. These results did not support our hypothesis. Stx binding to kidney tissues from newborn calves correlated with the presence of Gb3, a receptor for Stx, in these tissues. However, in spite of clear evidence that calf brains also contain Gb3, we did not detect Stx binding to brain tissues by the overlay assay. The lack of Stx binding and of Gb3 in intestinal tissues raised questions about the effects of Stx in calf intestines. Stx did not cause fluid accumulation in ligated ileal loops in newborn calves and experimental infection of calves with O157:H7 did not result in premature death of intestinal epithelial cells. Differences in Stx receptivity and toxicity may explain why systemic manifestations of STEC infection that occur in other species are not seen in cattle with STEC infection. This will benefit researchers, diagnosticians, and veterinarians.
Technical Abstract: Virulence of Escherichia coli O157:H7 is associated with the production of Shiga toxins (Stx1 and Stx2) and expression of their preferred receptor, globotriaosyl ceramide (Gb3). Immunohistochemistry was used to define the binding of Stx1 and Stx2 overlaid on to frozen bovine tissue. Stx1 and Stx2 bound to distal convoluted tubules in the renal cortex from both, newborn and adult cattle. Shiga toxins also bound to epithelium in selected areas of the duodenum. However, Shiga toxins did not bind to the epithelium in gastrointestinal sites other than the duodenum, nor did they bind to blood vessels in any of the 6 intestinal and 5 extraintestinal organs examined. The lack of in vitro receptivity of vasculature and enterocytes raised questions as to the enterotoxicity and cytotoxicity of Shiga toxins in calf intestine. Neither viable E. coli O157:H7 nor Shiga toxin-containing crude extracts caused fluid accumulation in ligated ileal loops in newborn calves. Additionally, there was only a slight and inconsistent increase of enterocyte apoptosis in newborn calves that developed enteritis following oral inoculation with E. coli O157:H7. We suggest that the lack of enterocyte and vascular receptivity for Shiga toxins may be an explanation as to why E. coli O157:H7 infections are usually asymptomatic in cattle and why systemic vascular lesions have not been reported in Shiga toxin-producing E. coli (STEC) infections in cattle.