Abstract
Enteropathogenic Escherichia coli (EPEC) strains cause watery diarrhea almost exclusively in young children. The basis for this age discrimination has never been determined, but it may be related to host cell receptors. During infection, EPEC strains express type IV bundle-forming pili composed of repeating subunits of the protein called bundlin. The very first interaction between EPEC and in vitro-cultured epithelial cells is mediated by the binding of alpha-bundlin to a carbohydrate receptor that contains, at a minimum, the N-acetyllactosamine (LacNAc) glycan sequence. However, bundlins expressed from the beta-bundlin allele do not bind LacNAc glycan sequences. Herein, we investigated whether EPEC strains use alpha-bundlin to mediate early adherence to human intestinal biopsy specimens cultured in vitro by assessing the ability of isogenic EPEC mutants expressing either the alpha(1)- or beta(1)-bundlin allele or a bundlin-deficient EPEC strain to bind to these specimens. Furthermore, we directly compared the abilities of a wild-type EPEC strain to bind to the epithelial surfaces of both human adult and pediatric biopsy specimens. Our results demonstrate that beta-bundlin does not act as an adhesin during early EPEC adherence to adult duodenal biopsy specimens. The results also indicate that EPEC binds equally well to adult and pediatric biopsy specimens in an early adherence assay. This result is supported by the finding that the early adherence of EPEC to both adult and pediatric biopsy specimens was inhibited by LacNAc neoglycoconjugates, suggesting that organisms expressing alpha-bundlin-type bundle-forming pili initially bind to related glycan receptors in both age groups.