The role of protein, RNA and DNA synthesis in the repair of thermal injury in Salmonella typhrimurium was investigated. Thermal injury was assessed by the ‘minimal medium recovery’ system: after heat treatment, higher viable counts are obtained on minimal-medium agar than on complex-medium agar, and the ability of heated bacteria to form colonies on complex-medium agar is recovered when they are incubated in liquid minimal medium. This recovery is inhibited by rifampin and chloramphenicol, but not by nalidixic acid. In addition, rifampin causes a loss in viability. Alkaline sedimentation analyses of radioactively labelled DNA showed that hydroxyurea and rifampin, unlike chloramphenicol and nalidixic acid, cause DNA breaks in heated bacteria. The results indicate that rifampin is lethal to heated bacteria and that chloramphenicol, though not lethal, prevents repair of thermal damage.
