Abstract

This report describes variations in the levels of groups of facultatively anaerobic bacteria in the intestinal tract and the relative weights of caecum, thymus and spleen in N:NIH mice and Riv:TOX rats kept under SPF conditions. Considerable variation in the composition of the enteric bacterial flora of mice and rats was detected. The possible influence of a poor colonization resistant (strictly anaerobic) flora (mCRF) on levels of other enteric flora elements and on relative weights of lymphoid organs is discussed.