Effect of penicillin on the succession, attachment, and morphology of segmented, filamentous microbes in the murine small bowel.

Indigenous segmented filamentous microbes attach to murine ileal epithelial cells. These microbes can be seen on the epithelial surface with a scanning electron microscope. They colonize preferentially the distal ileum in mice. Penicillin, placed in the animal's drinking water, eliminates the microbes from the mouse ileum, but recolinization of the ileum is observed 4 to 5 weeks after the penicillin treatment is stopped. Within 3 to 5 h after rats are given penicillin, the morphology of the microbes is changed. Their external surfaces are wrinkled or broken. Vacated and partially vacated attachment sites are observed. Almost all of the organisms disappear from murine ilea after the animals are exposed to penicillin for 10 h. These observations are discussed in relation to the microbe itself and in its interaction with ileal epithelial cells.