Inactivation of Dried Bacteria and Bacterial Spores by Means of Gamma Irradiation at High Temperatures

Abstract

Dried preparations with Streptococcus faecium , strain A 2 1, and spores of Bacillus sphaericus , strain C I A, normally used for control of the microbiological efficiency of radiation sterilization plants and preparations with spores of Bacillus subtilis , normally used for control of sterilization by dry heat, formalin, and ethylene oxide, as well as similar preparations with Micrococcus radiodurans , strain R 1 , and spores of Bacillus globigii ( B. subtilis , var. niger ) were gamma irradiated with dose rates from 16 to 70 krad/h at temperatures from 60 to 100 C. At 80 C the radiation response of the spore preparations was the same as at room temperature, whereas the radiation resistance of the preparations with the two vegetative strains was reduced. At 100 C the radiation response of preparations with spores of B. subtilis was unaffected by the high temperature, whereas at 16 and and 25 krad/h the radiation resistance of the radiation-resistant sporeformer B. sphaericus , strain C I A, was reduced to the level of radiation resistance of preparations with spores of B. subtilis . It is concluded that combinations of heat and gamma irradiation at the temperatures and dose rates tested may have very few practical applications in sterilization of medical equipment.