INCREASING THE INTESTINAL RESISTANCE OF RATS TO THE INVASIVE PATHOGENSALMONELLA-ENTERITIDIS - ADDITIVE EFFECTS OF DIETARY LACTULOSE AND CALCIUM

Background and aims-Lactulose fermentation by the intestinal microflor a acidifies the gut contents, resulting in an increased resistance to colonisation by acid sensitive pathogens. The extent of fermentation s hould be controlled to prevent acid induced epithelial cell damage. Co nsidering the buffering capacity of calcium phosphate and its intestin al cytoprotective effects, whether supplemental calcium phosphate adds to the increased resistance to intestinal infections by lactulose fer mentation was studied. Methods-In a strictly controlled experiment, ra ts were fed a purified low calcium control diet, a low calcium/lactulo se diet, or a high calcium/lactulose diet, and subsequently infected o rally with Salmonella enteritidis. Results-Lactulose fermentation lowe red the pH and increased the lactic acid concentration of the intestin al contents, which significantly reduced excretion of this pathogen in faeces; thus it improved the resistance to colonisation. This agreed with the high sensitivity of S enteritidis to lactic acid (main metabo lite of lactulose fermentation) in vitro. Calcium phosphate decreased translocation of S enteritidis to the systemic circulation, an effect independent of lactulose. The unfavourable increased cytotoxicity of f aecal water caused by lactulose fermentation was more than counteracte d by supplemental calcium phosphate. Moreover, calcium phosphate stimu lated lactulose fermentation, as judged by the reduced lactulose excre tion in faeces and increased lactic acid, ammonia, and faecal nitrogen excretion. Conclusion-Extra calcium phosphate added to a lactulose di et improves the resistance to colonisation and translocation of S ente ritidis. This is probably mediated by a calcium induced stimulation of lactulose fermentation by the intestinal microflora and reversion of the lactulose mediated increased luminal cytotoxicity, which reduces d amage inflicted on the intestinal mucosa.