Inactivation of Bacillus Spores by Ultraviolet or Gamma Radiation

Bacillus anthracis spores represent an important bioterrorism agent that can be dispersed in air or water. Existing decontamination practices based on these spores have focused on chemical disinfectants; however, the basic characteristics of radiation-based disinfectants suggest potential advantages in their application for control of Bacillus spores. Experiments were conducted to examine the effectiveness of ultraviolet $\left({\mathrm{UV}}_{254}\right)$ radiation and $\gamma$ radiation for inactivation of Bacillus spores. Spores of Bacillus cereus were used for most experiments because of their similarity to B. anthracis. A limited number of experiments were also conducted using B. anthracis Sterne spores. In aqueous suspension, B. anthracis Sterne spores were observed to be slightly more resistant to ${\mathrm{UV}}_{254}$ than the spores of B. cereus. For the conditions of culture and assay used in these experiments, both spore types were more sensitive to ${\mathrm{UV}}_{254}$ radiation in aqueous suspension than the spores of B. subtilis, which are commonly used to characterize the performance of UV disinfection systems for water. Dried spores on surfaces were observed to be more resistant to ${\mathrm{UV}}_{254}$ than the same spores in aqueous suspension; it is likely that the increased resistance to UV of the dried spores was attributable to surface characteristics (porosity and texture) of the solid materials. $\gamma$ radiation was shown to accomplish similar rates of inactivation for spores in aqueous suspension and for dried spores on surfaces. Collectively, these results suggest that the application of UV or ionizing radiation may hold promise for decontamination following bioterrorism events.