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The adherence of radiolabeled fimbriated (S 7471 OF) and nonfimbriated (S 7471 N) Salmonella typhimurium to small intestinal rat enterocytes was examined during postnatal development. The fimbriated strain invariably adhered in higher numbers than the nonfimbriated strain during all periods of development. The capability of enterocytes to bind Salmonella increased significantly during postnatal development and reached adult levels at weaning time (21 days of age). Bacterial adherence to enterocytes was similar if the cells were isolated from the proximal or the distal small intestine. Early weaning of pups did not affect the capability of enterocytes to bind Salmonella. Pretreatment of isolated enterocytes from adult animals with rat's milk before exposure to Salmonella had no effect on the level of bacteria that adhered per enterocyte. Conversely, pretreatment of Salmonella with rats' milk before binding to enterocytes from adult animals also did not alter the level of bacteria adhered per enterocyte. These results suggest an age-dependent, postnatal development of available receptors for S. typhimurium on rat enterocytes. The acquisition of these receptors is not affected by mother's milk and is unaltered by early weaning.

A number of dietary lectins have been shown to resist proteolytic digestion. These lectins interact with the small intestinal mucosa causing structural and functional changes. Concomitant to these changes, bacterial overgrowth was reported and a possible interaction between lectins and bacteria in the small intestine was postulated. The aim of this study was to investigate the effect of various lectins on adherence of Salmonella typhimurium to both isolated small intestinal enterocytes and ligated intestinal loops. Isolated intestinal cells or ligated intestinal loops were incubated with ['HI adenine-S. typhimuriurn in the presence or absence of concanavalin A, phytohemagglutinin, peanut agglutinin, and wheat germ agglutinin. Only concanavalin A promoted the adherence of various strains of nonfimbriated S. typhimurium to isolated viable intestinal cells. Other lectins showed no effect on the adherence. In situ studies showed that bacterial binding was increased in concanavalin A-treated intestinal loops, supporting the significance of the experiments in vitro. These data suggest that lectins may act by promoting bacterial adherence to the small intestine, thereby facilitating colonization and infection, and leading to bacterial overgrowth. [P.S.E.B.M. 1989, Vol1921he widespread presence of lectins in dietary foods has prompted a number of investigators to ex-

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The adherence of fimbriated (Fim+) and nonfimbriated (Fim-) strains of Salmonella typhimurium to both isolated intestinal epithelial cells and intact intestinal mucosa of healthy and malnourished rats was investigated. Fim+ strains bound in significantly higher numbers than did Fim- strains to enterocytes isolated either from healthy or malnourished rats. Adherence to intact intestinal mucosa in situ was demonstrable with both Fim+ and Fim- bacteria, but Fim+ strains were preferred because they showed approximately twofold higher numbers of adhered bacteria compared to Fim- strains. Additionally, bacterial adherence to intact mucosa in situ was consistently higher in well-fed controls than in malnourished rats. Ultrastructural studies revealed marked cell destruction and lysis in malnourished rats, whereas no histological change was detected in the mucosa of control animals. These results suggest that malnutrition may lead to altered intestinal cell surfaces, thus increasing their susceptibility to infection through mechanisms that are different from adherence.