However, increased abundance, activity, or presence of certain mucin-degrading bacteria has been associated with detrimental effects in some models, including increasing pathogen susceptibility (5, 12), development of spontaneous colitis like that which occurs in inflammatory bowel diseases (IBDs) (13), increased allergen sensitivity (14), and higher mortality due to carbapenem-associated graft vs. host disease (15). This evidence concerns the gene MUC5AC and inflammatory bowel disease.