Lethal and Dissociative Effects of X-Rays on Bacteria

Abstract

Cultures of Staphylococ-cus aureus and Serratia marcescens were purified by single-cell isolation and treated with the soft and hard rays of Cu and the hard rays of Mo. When numbers representing the % of cells surviving x-ray treatment were plotted on semi-logarithmic paper against the time of exposure, a straight line was obtained, indicating that the lethal effects of x-rays are dependent on the number of bacteria present at any given time. The hard rays used in this study were more effective in killing bacteria than the soft rays of the same intensity. X-rays increased the dissociation rates of Staph. aureus and Serratia marcescens, but the kind or number of variants that resulted from x-ray treatment could not be predicted. Actively proliferating cells showed a greater tendency to form dissociants after irradiation than non-proliferating cells. Occasionally streptococcus-like forms resulted from irradiation of Staph. aureus. Paraffin-cellulose vials were used as containers for irradiating the bacterial suspensions and cultures.