Reactivation of chlorine-inactivated Escherichia coli.

AVarious investigators have shown that irradiated bacterial cells can be reactivated by different nutrients. However, a controversy exists as to whether chlorinekilled bacteria can be made to recover by posttreatment. Heinmets et al. (1954) reported that they were able to restore the viability of chlorine-inactivated Escherichia coli strain B/r by incubating cells suspended in buffer supplemented with certain tricarboxylic acid cycle intermediates. The bacterial suspensions were incubated at 37 C for 24 hr and then plated out on minimal agar. No living bacteria were detected in buffer suspensions or in nutrient broth, whereas viable cells (up to 106) were found in buffer supplemented with tricarboxylic acid cycle intermediates. However, when plating was performed immediately without intermediate incubation (for 24 hr) in liquid medium, no reactivation occurred even if the plating agar was reinforced with the above-mentioned metabolites. The validity of these results was questioned by Garvie (1955), who showed that E. coli strain 28D10 cotuld multiply in phosphate buffer and that the growth was enhanced by various Krebs cycle intermediates. Furthermore, addition of dead bacteria improved growth to some extent. Chambers et al. (1957) doubted the ability to achieve reactivation of chlorine-killed bacteria. These investigators were able to "reactivate" chlorine-'4killed" bacteria, provided some survivors remained after treatment with chlorine. However, when no survivors were left from exposure to the disinfectant, no reactivation was obtained on addition of Krebs cycle intermediates. The growth obtained with the lower concentration of chlorine was interpreted as due to multiplication of survivors in the incubation mixture, rather than reactivation. A similar conclusion that reactivation as described by Heinmets did not occur was reached by Hurwitz et al. (1957). In the following experiments we attempted to reactivate chlorine-killed bacteria by plating them on different solid media immediately after exposure to chlorine.