Bacterial localization in the caecum of the rabbit.

The indigenous microflora of the rabbit caecum and its associated microenvironments has been examined using transmission electron microscopy. Rods and coccoid forms predominated in the caecal lumen and in association with the lining epithelial cell surfaces. In certain areas a curved flagellate rod-like form occurred in numbers and these exhibited features reminiscent of spirochaetes. The caecal crypts showed a homogeneous population of a monotypic spiral form similar to that found in caecal crypts of certain other mammals. In several cases, fusiform bacteria were found within the apical region of intact epithelial cells. There was no evidence of host reaction and the organisms appeared to be undergoing resting spore formation.