MIXED-FIELD NEUTRONS AND GAMMA-PHOTONS INDUCE DIFFERENT CHANGES IN ILEAL BACTERIA AND CORRELATED SEPSIS IN MICE

High doses of radiation induce septicaemia, from bacterial translocati on, and death in animals. Mice were exposed to either comparable letha l (LD(90/30)) or sublethal (LD(0/30)) doses of mixed-field [n/(n + gam ma) = 0.67] or pure Co-60 gamma-photon radiation. The relative biologi cal effectiveness of these comparable doses of radiation was 1.82, det ermined by probit analysis. Mice given a lethal dose of mixed-field ra diation developed a significant (p < 0.01), 10(9)-fold increase in Gra m-negative facultative bacteria in their ilea over values in control m ice. In contrast, mice given a lethal dose of gamma-photon radiation d eveloped a significant (P < 0.01) increase in only Gram-positive bacte ria in their ilea, while the number of Gram-negative bacteria remained near values in control mice. Data correlated with bacteria that were isolated and identified from the livers of mice that were given compar able lethal doses (LD(99/30)) of mixed-field or gamma-photon radiation . In sublethally irradiated mice, fluctuation in the total number of b acteria was detected in their ilea during the first week following irr adiation, after which the number approximated the value in control mic e. This difference in the predominant facultative bacteria in ilea res ulting from different qualities of radiation has important implication s for the treatment of septicaemic-irradiated hosts.