Effect of Sodium Chloride on the Heat and Radiation Resistance and on the Recovery of Heated or Irradiated Spores of the Genus Bacillus

Summary. Increasing concentrations (2, 4 and 8% w/v) of NaCl in the heating medium reduced the heat resistance of spores of Bacillus stearothermophilus but had no effect on the heat or radiation resistances of B. pumilus, B. subtilis and B. subtilis var. niger or on the radiation resistance of B. stearothermophilus. Increasing heat damage rendered all the spores increasingly sensitive to NaCl in the recovery medium. The presence of NaCl during heating reduced the subsequent NaCl sensitivity of B. pumilus, B. subtilis and B. subtilis var. niger but increased that of B. stearothermophilus. Increasing doses of γ radiation rendered the spores of B. stearothermophilus increasingly sensitive to NaCl in the recovery medium. The effect was less pronounced with B. pumilus , whilst B. subtilis and B. subtilis var. niger showed little change in their post‐irradiation sensitivity to NaCl. The presence of NaCl during γ irradiation had no effect on the subsequent pattern of postirradiation NaCl sensitivity.