Radiation inactivation of Paenibacillus larvae and sterilization of American Foul Brood (AFB) infected hives using Co-60 gamma rays

The effectiveness of gamma radiation in inactivating the Philippine isolate of Paenibacillus larvae was investigated. Spores of P. larvae were irradiated at incremental doses (0.1, 0.2, 0.4, 0.8 and 1.6 kGy) of gamma radiation emitted by a 60Co source. Surviving spores were counted and used to estimate the decimal reduction (D10) value. A dose of 0.2 kGy was sufficient to inactivate 90% of the total recoverable spores from an initial count of 105–9×103 spores per glass plate. The sterilizing effect of high doses of gamma radiation on the spores of P. larvae in infected hives was determined. In this study, a minimum dose (Dmin) of 15 kGy was tested. Beehives with sub-clinical infections of AFB were irradiated and examined for sterility. All the materials were found to be free of P. larvae indicating its susceptibility to γ-rays. After irradiation, there were no visible changes in the physical appearance of the hives’ body, wax and frames. Thus, a dose of 15 kGy is effective enough for sterilization of AFB-infected materials.

► We characterized Paenibacillus larvae and determined its radiation sensitivity.
► We investigated the effectiveness of gamma rays in inactivating P. larvae.
► Gamma radiation inactivates P. larvae.
► 15 kGy is effective for the sterilization of P. larvae-infected hives.
► Irradiation produces no visible changes in the hives’ body, waxes and frames.