Radiosensitization and radioprotection of E. coli by alcohols

The survival of E. coli K12 strain AB1157 and the isogenic repair-deficient mutant E. coli AB2480 (recA13, uvrA6) was measured after gamma-irradiation in the presence of various alcohols as well as after incubation and subsequent removal of the alcohols before irradiation. Irradiation in the presence of alcohols leads to the already known protection effect, which has been attributed to OH radical scavenging. However, it was not possible to explain the protection solely in terms of the reactivity of the OH radical with the various alcohols, because addition of some of the alcohols did not yield the expected survival values. It was found that incubation with and subsequent removal of various alcohols before irradiation led to radiosensitization. The degree of radiosensitization increases with the hydrophobicity of the alcohol. In the case of glycerol no radiosensitization was observed. We can conclude that alcohols protect predominantly by OH radical scavenging. The comparatively small protection of cell survival by the more hydrophobic alcohols can be attributed to the sensitizing effect of these alcohols.