The Established Intimin Receptor Tir and the Putative Eucaryotic Intimin Receptors Nucleolin and β1 Integrin Localize at or near the Site of Enterohemorrhagic Escherichia coli O157:H7 Adherence to Enterocytes In Vivo

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Abstract
For enterohemorrhagic Escherichia coli (EHEC) O157:H7 to adhere tightly to the intestinal epithelium and produce attach and efface (A/E) lesions, the organism must express the adhesin intimin and insert the bacterially encoded translocated intimin receptor Tir into the plasma membrane of the host enterocyte. Additionally, some reports based on tissue culture experiments indicate that intimin has affinity for the eucaryotic proteins nucleolin and β1 integrin. To address the potential biological relevance of these eucaryotic proteins in the infection process in vivo, we sought to compare the proximity of Tir, nucleolin, and β1 integrin to regions of EHEC O157:H7 attachment in intestinal sections from three different inoculated animals: piglets, neonatal calves, and mice. Piglets and neonatal calves were chosen because intimin-mediated adherence of EHEC O157:H7 and subsequent A/E lesion formation occur at high levels in these animals. Mice were selected because of their ease of manipulation but only after we first demonstrated that in competition with the normal mouse gut flora, an EHEC O157:H7 strain with a nonpolar deletion in the intimin gene was cleared faster than strains that produced wild-type or hybrid intimin. In all three animal species, we noted immunostained Tir beneath and stained nucleolin closely associated with adherent bacteria in intestinal sections. We also observed immunostained β1 integrin clustered at locations of bacterial adherence in porcine and bovine tissue. These findings indicate that nucleolin and β1 integrin are present on the luminal surface of intestinal epithelia and are potentially accessible as receptors for intimin during EHEC O157:H7 infection.

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