P-162 Pathobiont Induced Changes in Mucosal Homeostasis and Bacterial Community Structure in Defined Microbiota Mice

Abstract

BACKGROUND: The gastrointestinal microbiota is inherited from our mothers during the birthing process and throughout the postnatal period. Few studies have evaluated heritability of changes in the structure and function of the microbiota following introduction of a pathobiont and/or induction of colitis across successive generations. The goals of this study were to utilize immunologically competent, gnotobiotic C3H/HeN:TAC mice colonized with a defined microbiota (DM) (i.e., altered Schaedler flora ASF]) as a murine model to evaluate changes in the community structure of the ASF as well as in the susceptibility to DSS-induced colitis following colonization with E. coli LF82. LF82 is an adherent invasive E. coli (AIEC) strain that has been isolated from 30 to 40% of patients with ileal Crohn's disease. We hypothesized that colonization of DM mice with LF82 via vertical transmission will disrupt the homeostasis of the resident microbiota (i.e., ASF) and predispose the host to more severe inflammatory responses subsequent to exposure to DSS. METHOD(S): Adult DM mice were colonized with LF82 by oral gavage, maintained in gnotobiotic isolators, and bred for 4 generations. These mice and subsequent offspring were divided to 2 populations with 1 group chronically treated with DSS prior to breeding. Fecal samples from breeding females were collected throughout the generations at multiple timepoints. DNA was extracted from fecal and cecal samples and submitted for 16S sequencing. QIIME was used for analysis of microbial abundance. Fluorescent in situ hybridization (FISH) was used to evaluate spatial rearrangement of the microbiota. Mice from each generation (i.e. mice colonized with LF82 as pups) were treated with 2% DSS and evaluated for severity of colitis in comparison to mice colonized with LF82 as an adult and control DM mice treated with 2% DSS. Colonic tissues, peripheral blood, and mesenteric lymph nodes were harvested to assess host gene expression, cytokine production, histological evaluation, and adaptive immune responses. RESULT(S): Based on metagenomic analysis and FISH, colonization of the DM mice with LF82 altered the abundance of several ASF in subsequent generations. In addition, the abundance of LF82 increased between the F1 and F3 generations and this correlated with an increased host immune response to LF82 antigens. Following exposure to DSS, more severe histologic inflammation was present in the colonic tissue of mice colonized with LF82 as pups compared to mice colonized with LF82 as adults. The more severe colitis (i.e, transmural) was accompanied by elevated levels of IL-17 in the colonic mucosa and the presence of activated CD4 T cells. CONCLUSION(S): We conclude that (1) LF82 chronically colonizes DM mice and is transmissible from dam to offspring over at least 4 generations, (2) colonization with LF82, in the presence or absence of DSS treatment, alters ASF community structure that is heritable from 1 generation to the next, and (3) young mice colonized with LF82 by vertical transmission develop more severe inflammation post-DSS exposure as compared to mice colonized with LF82 as an adult.