Investigating Gut Microbiota-Host Interactions in a Microaerobic Environment

The gut microbiota has an important role in maintaining intestinal health and protecting against enteric infections (colonisation resistance). Nevertheless the majority of these interactions haven't been explored, largely due to a lack of experimental model systems that can culture oxygen-sensitive commensals alongside intestinal cells. In this project, we have established a novel in vitro model system of the human intestinal epithelium (Vertical Diffusion Chamber, VDC) which also supports growth of strictly anaerobic bacteria. We have applied this system to investigate the interactions of gut symbiont Ruminococcus gnavus with a functioning mucus-producing epithelium, established using T84 and goblet-like LS174T cell lines, and its effect on infection with foodborne pathogen enteropathogenic E. coli (EPEC). Initial work focused on identifying a culture medium that supports R. gnavus and EPEC growth whilst maintaining epithelial integrity and barrier function. This has been achieved by establishing bacterial growth curves in different media and assessing epithelial barrier function by transepithelial electrical resistance and immunofluorescence staining (IFS) of tight-junction protein occludin. Further IFS demonstrated that introduction of LS174T cells to the epithelium causes mucin secretion and facilitates colonisation by R. gnavus. Co-culture of EPEC with R. gnavus reduces numbers of viable and adherent EPEC, but only when LS174T are present. These data indicate potential colonisation resistance activity by R. gnavus, discovered by utilising a model system that supports anaerobic culture and a functioning epithelium side-by-side. Future work will investigate colonisation resistance activity for a panel of R. gnavus strains and attempt to elucidate mechanisms behind this activity.