Inflammatory bowel disease

(A, a) Crohn disease. A prolific bacterial biofilm covers the colonic mucosa, multicolor FISH: Bacteroides is orange, Eubacterium rectale and Faecalibacterium prausnitzii are both red, all other groups are green. Despite close attachment to the mucosa, no bacteria can be found intracellularly in the columnar epithelium or submucosa.
(B) Ulcerative colitis, cytopathogenic effects of bacterial adhesion, with defects (ulcerations) of the epithelial layer and migration of bacteria into the submucosa. Despite the severe inflammation, the number of bacteria is reduced compared to regions without marked inflammation as shown in panels A/a (x1000).
(b) DAPI stain, only a few leukocytes are seen in the biofilm. A prolific biofilm without a leukocyte response is typical for inflammatory bowel disease patients treated with azathioprine.