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Appl Environ Microbiol. 1974 May; 27(5): 830-833
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

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

Accelerator Department, Danish Atomic Energy Commission, Research Establishment Risø, DK-4000 Roskilde, Denmark

ABSTRACT

Dried preparations with Streptococcus faecium, strain A₂1, and spores of Bacillus sphaericus, strain C_IA, 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 R₁, 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_IA, 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.

¹ Present address: Novo Industri A/S, Screening Laboratory, Enzyme Division, Novo Allé, DK-2800 Bagsvaerd, Denmark.