Abstract
Human inflammatory bowel disease (IBD) is a chronic intestinal disease where the resident microbiota contributes to disease development, yet the specific mechanisms remain unclear. Interleukin-10 gene-deficient (Il10-/-) mice develop inflammation similar to IBD, due in part to an inappropriate response to commensal bacteria. We have previously reported changes in intestinal morphology and colonic gene expression in Il10-/- mice in response to oral bacterial inoculation. In this study, we aimed to identify specific changes in the caecal microbiota associated with colonic inflammation in these mice. The microbiota was evaluated using pyrotag sequencing, denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR. Microbiota profiles were influenced by genotype of the mice and by bacterial inoculation, and a strong correlation was observed between the microbiota and colonic inflammation scores. Although un-inoculated Il10-/- and C57 mice had similar microbiota communities, bacterial inoculation resulted in different changes to the microbiota in Il10-/- and C57 mice. Inoculated Il10-/- mice had significantly less total bacteria than un-inoculated Il10-/- mice, with a strong negative correlation between total bacterial numbers, relative abundance of Escherichia/Shigella, microbiota diversity, and colonic inflammation score. Our results show a putative causative role for the microbiota in the development of IBD, with potentially key roles for Akkermansia, or for Bacteroides, Helicobacter, Parabacteroides, and Alistipes, depending on the composition of the bacterial inoculum. These data support the use of bacterially-inoculated Il10-/- mice as an appropriate model to investigate human IBD.
Highlights
The term “inflammatory bowel disease” (IBD) refers to inappropriate and exaggerated immune-mediated disorders characterised by chronic and relapsing inflammation of the gastrointestinal tract, including Crohn’s disease (CD) and ulcerative colitis (UC)
While the conventional intestinal flora (CIF) inoculum has not been characterised (e.g., colony forming units (CFU) within this inoculum were not assessed), the mice from which this was obtained were acquired from the same source for all subsequent studies using this protocol, and we have demonstrated a consistent effect on colon inflammation [20,24,25,26,27] and microbiota profile [28] in response to the E. faecium strains (EF).CIF inoculation
Our results show that an oral inoculation with a bacterial preparation (EF, CIF or EF.CIF) caused major changes in the caecal microbiota of Il10-/- mice compared with un-inoculated (C and SPF)
Summary
The term “inflammatory bowel disease” (IBD) refers to inappropriate and exaggerated immune-mediated disorders characterised by chronic and relapsing inflammation of the gastrointestinal tract, including Crohn’s disease (CD) and ulcerative colitis (UC). Studies using animal models of intestinal inflammation such as the Il10-/- mouse have been crucial in extending our understanding of the pathogenesis of IBD, to dissect the roles of specific bacteria and bacterial factors. Intestinal inflammation in Il10-/- mice can be induced by specific bacterial strains including enterococci [13,14,15], E. coli [14,15], or Bacteroides vulgatus [11]. These observations led us to examine whether inoculating Il10-/- mice (C57 background) with Enterococcus species would result in the development of intestinal inflammation, and be an appropriate model of human IBD
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