Microbial flora of the mouse ileum mucous layer and epithelial surface.

We have developed new methods to minimize fluid shear during preparation of specimens for electron microscopy and to retain the mucous blanket that covers the tissue surface of the ileum in mice. We also used general stabilization by nonspecific antibodies to minimize the collapse of the mucous layer during dehydration for electron microscopy. These methods allowed us to visualize the gradual progression of the mucous blanket from a thin diaphanous layer in newborn animals to a very thick (ca. 50 micrometers), coherent structure in older animals that contained a mixed population of bacteria and protozoa. Some bacteria, notably filamentous forms, were patently anchored to the epithelial tissue but projected into the mucous blanket, whereas others clearly existed within the mucous blanket and were unattached to the epithelial surface. Similarly, some protozoa were firmly attached to the tissue surface, whereas others were suspended in the viscous mucous blanket. In an adult animal, the mucous blanket was a very thick layer which actually occluded most of the tissue surface and contained a rich variety of bacteria and protozoa.