Mucus and its gel-forming glycoprotein component, mucin, are thought to protect the gastrointestinal tract from enteric pathogens by inhibiting their attachment to enterocytes. In this study, we investigated interactions between Yersinia enterocolitica (isogenic strains of virulent and nonvirulent organisms) and crude mucus, highly purified mucin, and brush border membranes (BBMs) isolated from the upper mid-, and distal small intestine and the proximal colon of the rabbit. Adherence of radiolabeled bacteria was assessed to BBMs, mucus, and mucin immobilized in polystyrene microtiter plate wells. Virulent Y. enterocolitica showed saturable binding to mucus, mucin, and BBMs from all four regions of the intestinal tract, although adherence to BBMs was appreciably greater than that to mucus or mucin. Maximal binding of bacteria was higher to BBMs from the distal small intestine and the proximal colon than to those from the upper and mid-small intestine, which may in part explain why the organism localizes to the ileo-caecal regions of the gut. Adherence of virulent Y. enterocolitica to BBMs was significantly reduced in the presence of homologous mucus or mucin preparations. Binding of virulent bacteria appears to depend on plasmid-encoded proteins located on the outer surface membrane, since (i) the isogenic strain lacking the virulence plasmid showed markedly less binding to all BBM, mucus, and mucin preparations; (ii) growth of the virulent strain at 25 degrees C, which inactivates its plasmid, significantly diminished binding to BBMs, mucus, and mucin; and (iii) mild proteolysis substantially decreased adherence of virulent bacteria to BBMs. Compared with rabbit intestinal and colonic mucins, binding of virulent Y. enterocolitica was significantly greater to purified human intestinal mucin and significantly less to rat intestinal mucin. These findings provide support for the role of mucus and mucin in host defense by preventing adherence of virulent Y. enterocolitica to epithelial cell membranes
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