Figure 6. DSS treatment of mice allowed bacteria to penetrate into the firm mucus layer and come in direct contact with the epithelium.

(A) Mice were given FITC-DSS (3%, green) in the drinking water for 12 h. The distal colon was fixed and the sections were immunostained with anti-Muc2 antiserum and anti-rabbit-Alexa546 (red). The arrows point at FITC-DSS that has penetrated the inner stratified mucus layer (s). Large amounts of bacteria and FITC-DSS is shown in the outer loose mucus layer (o). Epithelial cells are marked (e). Scale bar is 25 µm. (B) Bacteria were stained with FISH using the general rRNA probe EUB338 conjugated to Alexa 555 (red) and the nuclear DNA stained with Sytox Green DNA stain (green). The picture shows massive amounts of bacteria in contact with the epithelial cells. Scale bar is 10 µm.