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 translocation, and death in animals. Mice were exposed to either comparable lethal (LD90/30) or sublethal (LD0/30) doses of mixed-field [n/(n + y) = 0.67] or pure 60Co gamma-photon radiation. The relative biological effectiveness of these comparable doses of radiation was 1.82, determined by probit analysis. Mice given a lethal dose of mixed-field radiation developed a significant (p < 0.01), 10(9)-fold increase in Gram-negative facultative bacteria in their ilea over values in control mice. In contrast, mice given a lethal dose of gamma-photon radiation developed a significant (p < 0.01) increase in only Gram-positive bacteria 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 comparable lethal doses (LD99/30) of mixed-field or gamma-photon radiation. In sublethally irradiated mice, fluctuation in the total number of bacteria was detected in their ilea during the first week following irradiation, after which the number approximated the value in control mice. This difference in the predominant facultative bacteria in ilea resulting from different qualities of radiation has important implications for the treatment of septicaemic-irradiated hosts.