Normal enteric bacteria, such as Escherichia coli and Enterococcus faecalis, frequently cause complicating infections in patients with shock and trauma. A common finding in these patients is increased intestinal epithelial permeability, and experiments with cultured enterocytes have shown that bacterial adherence to and internalization by enterocytes is increased following opening of enterocyte tight junctions, exposing the enterocyte lateral surface. Syndecan-1, expressed on the basolateral surface of human enterocytes, is a cell surface transmembrane proteoglycan that expresses heparan sulfate (HS) on its extracellular domain. Our working hypothesis is that HS chains of cell surface proteoglycans, and specifically syndecan-1, may act as an enterocyte receptor or co-receptor for a variety of enteric bacteria. Preliminary data indicated that,like human enterocytes, HS and syndecan-1 are prominently expressed on the basolateral surface of cultured HT-29 enterocytes but not Caco-2 enterocytes. Experiments with HT-29 enterocytes (designed to open enterocyte tight junctions and interfere with bacterial binding to the HS chains on syndecan-1) suggested that HS may be a receptor for gram-positive but not gram-negative bacteria. The HS analog heparin, and HS itself, inhibited adherence and internalization of gram-positive Listeria monocytogenes by HT-29 enterocytes, and experiments with related glycosaminoglycans indicated that this inhibition was specific for HS. Additional preliminary experiments with HT-29 enterocytes indicated that heparin and HS similarly inhibited internalization of gram-positive E. faecalis and Staphylococcus aureus, but not gram-negative Salmonella typhimurium, Proteus mirabilis, and E. coli. Heparin did not have a noticeable effect on internalization of any bacterial species using Caco-2 enterocytes, which express low levels of HS and syndecan-1 Other preliminary experiments indicated that heparin-treated L. monocytogenes was less invasive in orally inoculated mice than was untreated L monocytogenes. In this proposal several experimental tools are used to clarify the interactions of cultured enterocytes with a variety of gram-negative bacteria, while focusing on gram-positive L. monocytogenes, E. faecalis, and S. aureus. These tools include monoclonal antibodies, glycosamino glycans, and heparin disaccharides, and two cell lines transfected to over express syndecan-1, namely ARH-77 myeloma cells and Caco-2 enterocytes. Data from in vitro studies are used to design experiments in mice (outbred and syndecan-1 knockout) to clarify the role of HS and syndecan-1 in intestinal colonization and extra intestinal dissemination of enteric bacteria. Data from these experiments may indicate that enterocytes have a receptor (related to cell surface HS and perhaps syndecan-1) involved in adherence and internalization of a variety of gram-positive bacteria including E. faecalis and S. aureus.
