Figure 5.

(A) In a steady-state, the mucosal microbial communities are kept in check by the luminal bacteria, intestinal immune response and barrier function. An oxygen gradient exists within the intestinal environment, with the mucosal interface being largely aerobic and the intestinal lumen largely anaerobic. (B) During colitis, the intestinal barrier breaks down, increasing the oxygen content within the intestinal lumen and leading to the expansion of aerotolerant mucosal microbial communities, which spill over into the intestinal lumen and translocate across the intestinal epithelial barrier surface to trigger a strong anti-bacterial response.