To model inflammatory bowel disease, we assessed infection with Helicobacter hepaticus 3B1 (ATCC 51449) and a potential probiotic Lactobacillus reuteri (ATCC PTA-6475) in gnotobiotic B6.129P2-IL-10(tm1Cgn) (IL-10(-/-) ) mice. No typhlocolitis developed in germ-free controls (n=21) or in L. reuteri (n=8) or H. hepaticus (n=18) mono-associated mice for 20 weeks post-infection. As positive controls, three specific pathogen-free IL-10(-/-) mice dosed with H. hepaticus developed severe typhlocolitis within 11 weeks.