Figure 1.

Measurement of the inner mucus layer. The inner mucus (im) layer was defined as the region between the colonic epithelial microvilli (mv) surface and the region where gut bacteria appeared. The thickness was measured by drawing a horizontal line indicating the uppermost limit of the epithelium (E), followed by drawing a line perpendicular to the horizontal line until the first bacterium was encountered on the outer mucus (om) layer. The distance of the perpendicular line was measured to scale and was considered the thickness of the inner mucus layer