Relation of the indigenous flora of the small intestine of the rat to post-irradiation bacteremia.

There is general agreement that bacteremia occurs as one sequel to midlethal doses of whole body x-irradiation (Warren and Whipple, 1923; Mottram and Kingsbury, 1924; Chrom, 1935; Lawrence and Tennant, 1937; Bennett et al., 1949; Miller et al., 1951 Gonshery et al., 1953). This infection could occur as a terminal event in animals dying of radiation injury; however, the findings of Miller et al. (1951) support the view that the infection once initiated usually leads to death and is not an agonal event. This is further supported by the finding that treatment with antibiotics (Miller et al., 1950; Smith et al., 1953) reduces mortality from x-radiation, and by findings reported here. The bacteremia which develops after x-irradiation may be directly related to the failure of the animal's normal defense mechanisms against bacterial invasion. However, post-irradiation changes in the intestinal flora may also be of considerable significance to an understanding of the mechanism of development of the septicemia. This paper reports a study of changes in the flora of rat small intestine following whole body x-irradiation. The findings suggest an interrelationship between indigenous pleomorphic lactobacilli in the small intestine and the invasive gram negative bacteria associated with the postirradiation bacteremia. The finding of this interrelationship has led to the recognition of antimicrobial activity associated with the intestinal lactobacilli of the rat.