Mucosal homeostasis is altered in the ileum of gnotobiotic mice

The microbiome of the gastrointestinal tract is a vast collection of microorganisms implicated in numerous aspects of normal physiology and disease pathogenesis. The use of gnotobiotic mouse models, with single or specific communities of microbes comprising the microbiome, can enhance our understanding of the microbiome-host relationship. We hypothesized that gnotobiotic mice would exhibit differences in mucosal homeostasis when compared with mice with conventional flora (CF). Single-organism gnotobiotic mice were generated containing Escherichia coli MG1655, Akkermansia muciniphila, Bacteroides eggerthii, and Clostridium symbiosum, representing four of the major phyla present in the gastrointestinal tract. Distal ileal segments were harvested from adult mice, and histologic sections were H&E stained and used to measure villus height and crypt depth. Immunohistochemistry was performed with Ki67 and TUNEL as markers of proliferation and apoptosis, respectively. When compared to the ileum from CF mice, the ileum from all groups of gnotobiotic mice had significant increases in nearly all measured parameters. In addition, significant differences were seen among certain gnotobiotic groups for villus height, crypt depth, and apoptosis. Single-organism gnotobiotic mice demonstrate enhanced morphometric parameters compared with mice with CF and show differences in growth patterns among bacterial species. These findings suggest unique interactions between individual bacteria and the host animal which hold potential for future therapeutic strategies aimed at mucosal restoration. The mechanisms involved in this process therefore warrant further study.