Listeria Research in the 1960s: How Does Ionizing Radiation Mediate Infectious Disease?

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

Author(s): R. H. Stewart, J. F. Pribnow, M. S. Silverman

Source: Radiation Research, Vol. 24, No. 1 (Jan., 1965), pp. 96-107

Published by: Radiation Research Society

[excerpted from the article]

"It is well known that exposure to a single acute dose of total-body X-irradiation within the mid lethal 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...

 …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 chosen, since effects on susceptibility to infection could be observed without encountering deaths from the radiation. The microorganism used to study the effects of continuous exposure to low-dose y-radiation was Listeria monocytogenes. It has been shown (3) that susceptibility to infection with this organism is influenced by the state of general resistance and by many environmental and climatic factors. Lacking, however, are data on the effects of irradiation on susceptibility to infection.....

 RESULTS

"The susceptibility of mice to an airborne infection with Listeria monocytogenes increased after continuous exposure to y-radiation delivered at 1.0 to 1.5 rads/hour. The increase in susceptibility became greater, the larger the total radiation dose.

The LD50o(3f0o)r nonirradiated mice was 5.7 X 105 organisms, whereas after exposure to 500 and 1500 rads it dropped to 1.8 X 105 and 1.2 X 105, respectively.  

Further exposure to 2000 rads decreased the LD50(30) to 4.1 X 104. After 2500 rads it was 1.7 X 104, a 33-fold increase in susceptibility compared to that found in the nonirradiated mice.

The fate of inhaled L. monocytogenes in the lungs of irradiated (2000 rads) and nonirradiated mice was investigated at 4 hours after infection. Irrespective of the aerosol challenge dose, the lungs of irradiated mice reduced bacterial numbers by 61 % in this time, compared to 80 % for the nonirradiated animals...."