Effect of Water Treatment and Pseudomonas Infection on Mortality in Irradiated, Viral Antibody-Free Mice

Chlorination or acidification of drinking water has historically been used to prevent irradiated mice from succumbing to overwhelming infections caused by Pseudomonas organisms. We postulated that with the advent of viral antibody-free animals and the strict implementation of stringent husbandry practices, water treatment for these mice would no longer be required. To examine this, 40 viral antibody-free BDF1 mice determined to be Pseudomonas-negative were irradiated, and all mice were offered untreated municipal water. All mice had Pseudomonas culture-negative fecal and tissue specimens on postirradiation days 0, 5, 8, and 10. To determine how these mice would respond if exposed to Pseudomonas sp., 30 additional Pseudomonas-negative, viral antibody-free BDF1 mice were orally inoculated with 1.4 × 10⁵ P. aeruginosa organisms, then irradiated. Ten of the mice were offered acidified water (pH 2.4), 10 mice were offered autoclaved water, and 10 mice were offered untreated municipal water. One day after oral inoculation, all animals had positive fecal culture results for Pseudomonas organisms. Five days after irradiation, mortality was 100% for animals in the municipal water group, but only 50% for animals in the autoclaved and acidified water groups. By day 9, 20% of the animals remained in the acidified and autoclaved water groups and their fecal culture results were negative for Pseudomonas organisms. Similar to previous studies in conventional animals, these results support the idea that water acidification improves survivability of irradiated animals when Pseudomonas is present. This study also indicates that water treatment is not a necessary practice for prevention of Pseudomonas infection in viral antibody-free irradiated mice maintained under appropriate husbandry conditions.