Studies of intestinal microflora. VII. Effect of diet and fecal microbial flora on survival of animals exposed to x irradiation.

Changes in the numbers and ratios of bacteria in the feces of rats were produced by administration of three different diets-grain, meat alone, and meat plus lactose. After significant alterations in the intestinal flora had developed, the animals were exposed to a midlethal dose of X irradiation (1,550 R). This treatment led to 100% deaths in rats in which the numbers of coliforms were increased by diet prior to irradiation. Changes in the numbers of lactobacilli appeared to play no role in determining the responses to X-ray exposure. When little or no change was produced by diet and when "normal" microflora was present, the fatality rate was reduced to 60%, and the rate of deaths was retarded when compared with that of the animals in which coliforms were increased.