Bacillus subtilis spores reduce susceptibility to Citrobacter rodentium-mediated enteropathy in a mouse model

The present work was aimed at investigating whether Bacillus subtilis spores, widely used in probiotic as well as pharmaceutical preparations for mild gastrointestinal disorders, can suppress enteric infections. To address this issue, we developed a mouse model of infection using the mouse enteropathogen Citrobacter rodentium, a member of a family of human and animal pathogens which includes the clinically significant enteropathogenic (EPEC) and enterohemorrhagic (EHEC) Escherichia coli strains. This group of pathogens causes transmissible colonic hyperplasia by using attaching and effacing (A/E) lesions to colonize the host colon. Because of its similarities to human enteropathogens, C. rodentium is now widely used as an in vivo model for gastrointestinal infections. Swiss NIH mice were orally administered B. subtilis spores one day before infection with C. rodentium. Mice were sacrificed on day 15 after infection, and distal colon, liver and mesenteric lymph nodes were removed for bacteria counts, morphology, immunohistology and IFNγ mRNA analysis. We observed that spore predosing was effective in significantly decreasing infection and enteropathy in suckling mice infected with a dose of C. rodentium sufficient to cause colon colonization, crypt hyperplasia and high mortality rates. Moreover, in mice predosed with spores, the number of CD4+ cells and IFNγ transcript levels remained high. These results thus indicate that our newly established model of C. rodentium infection is a suitable system for analyzing the effects of probiotic bacteria on enteroinfections and that B. subtilis spores are efficient at reducing C. rodentium infection in mice, leaving unaltered the immune response against the pathogen.