Effect of Chronic Gamma Radiation on Airborne Infection of Mice with Listeria monocytogenes

Abstract

It is well known that exposure to a single acute dose of total-body X-irradiation within the midlethal range markedly increases the mouse's susceptibility to experimentally induced bacterial infection. In comparison, a paucity of information exists regarding the effects of continuous exposure to low doses of y-radiation. Hammond et al. (1) studied the effects of continuous exposure to low doses of 7yradiation on the susceptibility of mice to Pseudomonas infection. Animals exposed at rates of 69 and 128 r/day demonstrated an increased susceptibility to intraperitoneal challenge of the bacteria. At these levels, accumulated doses of 3845 and 2695 r, respectively, were obtained. Those exposed at 34 r/day accumulated 2140 r but showed no significant increase in susceptibility. A few deaths from the radiation alone were observed in the groups receiving 69 and 128 r/day, but none occurred among the mice exposed at 34 r/day. In a later study (2) the challenge inocula were graded by less than a tenfold dilution, as previously used, in an attempt to detect smaller changes in susceptibility. With this method it was shown that daily exposure to 15 r of y-radiation (1350 r accumulated) resulted in a slight but demonstrable increase in susceptibility to intraperitoneal inoculation of Pseudomonas. In the present study, accumulated radiation doses up to 2500 rads were obtained by continuous exposure at 24 to 34 rads/day. These levels of radiation exposure were