A) Distal colon of a conventional mouse stained with UEA-1 (green), DAPI (blue in epithelium, red in lumen), and FISH probes specific to Firmicutes (yellow) and Bacteroidales (maroon). The thick, continuous, laminated inner layer of mucus adheres to the epithelium and excludes bacteria.
B–C) Distal colon of a gnotobiotic mouse colonized with Bacteorides thetaiotaomicron fed a high-fiber diet (B) or polysaccharide-free diet (C) (Earle et al., 2015). The sections are stained with anti-MUC2 antibody and DAPI; images show the epithelium (blue), mucus (green), bacteria (red), and plant matter (yellow) in the lumen. The epithelial border (cyan) was identified using the software BacSpace (Earle et al., 2015). The mucus layer in (C) is thinner than in (B), likely due to its consumption by B. thetaiotaomicron.