Spirochetes autochthonous to the rat gastrointestinal tract.

Spirochetes are structurally unique microorganisms found in the gastrointestinal tracts of most mammals. In an attempt to determine the ecological status of these bacteria, enumeration and distribution of morphologically distinct spirochetes were studied in the tracts of conventional laboratory rats. Five different types were seen to colonize infant rats between 19 and 26 days of age and subsequently to form stable communities in all 15 adults examined. Two types were found predominantly in lumen contents of the large bowel. The other three were consistently seen in the mucous blanket, attached to enterocyte surfaces or deep in the glands of the cecum and proximal colon. One type inhabiting the mucosal environment was also seen to pass into and through epithelial cells with no detectable host response. We conclude that spirochetes fulfill all the criteria for autochthonicity to the rat gastrointestinal tract.