Dietary oligofructose and inulin protect mice from enteric and systemic pathogens and tumor inducers

Prebiotics induce changes in the population and metabolic characteristics of the gastrointestinal bacteria, modulate enteric and systemic immune functions, and provide laboratory rodents with resistance to carcinogens that promote colorectal cancer. There is less known about protection from other challenges. Therefore, mice of the B6C3F1 strain were fed for 6 wk a control diet with 100 g/kg cellulose or one of two experimental diets with the cellulose replaced entirely by the nondigestible oligosaccharides (NDO) oligofructose and inulin. From each diet, 25 mice were challenged by a promoter of colorectal cancer (1,2-dimethylhydrazine), B16F10 tumor cells, the enteric pathogen Candida albicans (enterically), or were infected systemically with Listeria monocytogenes or Salmonella typhimurium. The incidences of aberrant crypt foci in the distal colon after exposure to dimethylhdrazine for mice fed inulin (53%) and oligofructose (54%) were lower than in control mice (76%; P < 0.05), but the fructans did not reduce the incidence of lung tumors after injection of the B16F10 tumor cells. Mice fed the diets with fructans had 50% lower densities of C. albicans in the small intestine (P < 0.05). A systemic infection with L. monocytogenes caused nearly 30% mortality among control mice, but none of the mice fed inulin died, with survival intermediate for mice fed oligofructose. Mortality was higher for the systemic infection of S. typhimurium (>80% for control mice), but fewer of the mice fed inulin died (60%; P < 0.05), with mice fed oligofructose again intermediate. The mechanistic basis for the increased resistance provided by dietary NDO was not elucidated, but the findings are consistent with enhanced immune functions in response to changes in the composition and metabolic characteristics of the bacteria resident in the gastrointestinal tract.