Specifically, wild-type (WT) mice treated with dexamethasone, a synthetic glucocorticoid that is routinely used to treat IBD (379), shift to a gut microbiome with lower Bacteroidetes abundances, increased Actinobacteria (Bifidobacterium) and Firmicutes (Lactobacillus), and a decrease in a mucin-degrading microbe found in the murine intestine, Mucispirillum (378). This evidence concerns the gene MUC5AC and inflammatory bowel disease.