The Incidence of Bacteremia in Mice Subjected to Total Body X-Radiation

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Abstract
A total of 1627 male mice weighing from 18-22 g. were subjected to a single total body exposure of X-radiation; 585 animals received 600 r each, 1042 received 450 r. Beginning with the 2d postirradiation day, groups of surviving animals were sacrificed and aseptically obtained heart blood and spleen were cultured on nutrient agar, blood agar, Brewer''s fluid thioglycolate medium, or in tubes of brain-heart infusion under NaOH and pyrogallic acid. In all, 280 animals of the 600 r series and 595 of the 450 r series were killed and their tissues cultured. Simultaneous records were kept of the death rate due to irradiation, and blood and spleens of 35 and spleens only of 17 more unirradiated control animals were cultured. All bloods and spleens from control mice proved sterile. In the irradiated animals from 5-85% of the 600 r series, and from 0-54% of the 450 r series showed bacteremia. The percentage of positive cultures varied from day to day, but in both series the incidence of bacteremia paralleled the death rate, the highest incidence of bacteremia appearing on the day of highest death rate. There was some evidence that the bacteremias were more severe in the 600 r series than in the 450 r. Identification of colonies in inoculated media indicated that 42% of the bacteremias showed Paracolobactrum; 22% coliform bacteria; 13% Proteus; 9% Pseudomonas: 6% alpha-Streptococcus; 3% unidentified Gram-negative rods; 2% Alcaligenes; and 0.3% anaerobes. Of these forms, all but Pseudomonas proved to be regular members of the bacterial flora of the large colon in normal mice, thus indicating the lower intestinal tract to be the reservoir from which invasion of the blood stream occurred following irradiation.