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Nutrient Interactions and Toxicity

Dietary Calcium Phosphate Promotes Listeria monocytogenes Colonization and Translocation in Rats Fed Diets Containing Corn Oil but Not Milk Fat¹

R. Corinne Sprong^*2, Marco F. E. Hulstein^* and Roelof Van der Meer

^* Department of Flavour, Nutrition and Ingredients, NIZO Food Research, 6710 BA Ede, The Netherlands; and the Wageningen Center for Food Sciences, 6700 AN, Wageningen, The Netherlands

²To whom correspondence should be addressed. E-mail: sprong{at}nizo.nl.

Most Gram-positive bacteria are susceptible to the bactericidal action of fatty acids and bile acids. Because dietary calcium phosphate (CaP_i) lowers the intestinal concentration of these antimicrobial agents, high CaP_i intake may enhance intestinal colonization of Gram-positive pathogens and the subsequent pathogenesis. In this study, we tested this hypothesis in a rat model using Listeria monocytogenes. Rats were fed diets containing low (20 µmol/g diet) or high (160 µmol/g diet) amounts of CaP_i. Dietary fat was provided as corn oil or milk fat. Rats were orally inoculated with L. monocytogenes. When rats consumed diets containing corn oil, high CaP_i intake indeed stimulated colonization of L. monocytogenes and increased L. monocytogenes translocation and diarrhea. In addition, supplemental CaP_i enhanced ex vivo growth of L. monocytogenes in fecal extracts of rats fed corn oil diets, suggesting that high CaP_i intake decreased a luminal inhibitory factor. The concentrations of bile salts and fatty acids, which were highly listericidal in vitro, were indeed considerably decreased in fecal water of rats in the high calcium corn oil group. Surprisingly, dietary CaP_i did not affect colonization and translocation of L. monocytogenes in rats fed the milk fat diet, nor did CaP_i enhance ex vivo growth in fecal extracts. This absence of Listeria stimulation was associated with a lack of effect of dietary CaP_i on fecal soluble fatty acids. In addition, residual soluble bile salts were higher in rats fed the high CaP_i milk fat diet compared with the high CaP_i corn oil diet. These results suggest that the stimulating effect of CaP_i on L. monocytogenes infection depends on the type of dietary fat consumed.

KEY WORDS: • calcium • dietary fat • fatty acids • bile acids • infection • rats