1058 - the Probiotic Potential of Non-Toxigenic Bacteroides Fragilis to Prevent Colitis and Tumorigenesis

Background: Polysaccharide A (PSA), a highly immunogenic capsular component of nontoxigenic Bacteroides fragilis NCTC 9343 (NTBF), has been reported to promote host mucosal immune system development and to suppress inflammation in the gut.Thus, NTBF is proposed for probiotic development to prevent colitis and colorectal cancer.In stark contrast, enterotoxigenic Bacteroides fragilis (ETBF) is highly associated with inflammatory bowel disease and colorectal cancer, and in murine hosts, ETBF rapidly induces an acute interleukin (IL)-17 colitis and tumorigenesis.The interactions of these distinct B. fragilis molecular subtypes were studied to determine the impact of NTBF on ETBF disease.Methods: Specific pathogen free (SPF) C57BL/6 wild type (WT) and multiple intestinal neoplasia (Min Apc716+/- ) mice received different B. fragilis orogastric treatments: NTBF-->ETBF, DPSA NTBF-->ETBF, and NTBF+ETBF.At 2 weeks, WT mice were evaluated for cytokine gene expression (quantitative PCR), disease severity (histopathology), and fecal B. fragilis (quantitative PCR).At 3 months, Min mice were evaluated for tumor development and fecal B. fragilis (quantitative PCR).Immune responses were evaluated by flow cytometry.Mann-Whitney tests were used for statistical analyses.Results: In SPF WT and SPF Min mice, we show that B. fragilis sequential treatment (NTBF then ETBF three days later; NTBF-->ETBF) diminished colitis (P = 0.0007) and decreased tumor development (P = 0.0053), respectively.Abrogated disease severity in sequentially treated mice was attributed to NTBF strain dominance and decreased levels of IL-17A, but ETBF colonization prior to NTBF (ETBF-->NTBF) or simultaneous with NTBF (NTBF+ETBF) mitigated the anti-inflammatory effect of NTBF.For instance, NTBF+ETBF treated mice continued to exhibit severe colitis and pronounced tumor formation.Surprisingly, NTBF-mediated protection was independent of PSA, as sequentially infected mice receiving DPSA NTBF (DPSA NTBF-->ETBF) exhibited similar levels of protection from colitis (P = <0.0001)and tumorigenesis (P = 0.0043).Further, SPF WT and SPF Min mice singly colonized with PSA-competent or PSA-deficient NTBF exhibited a similar colonic accumulation of regulatory (FOXP3 +), IL-17A + , and IFN-g + T cells.Daily NTBF probiotic treatment of mice stably colonized with ETBF failed to disrupt pathogenic ETBF strain dominance and did not improve the health of ETBF-colonized mice.Our findings demonstrate that NTBF, independent of PSA, may offer protection against ETBF colitis but may not act as a valid therapeutic treatment.