The inhibiting effect of microwave radiation on Paenibacillus larvae spores suspended in water

The aim of this paper was to investigate the effects of microwave radiation on the viability of Paenibacillus larvae spores and to study the relationship between the microwave power consumption, the exposure time and the number of spores in the examined suspensions. Sterile distilled water suspensions were made using larval detritus, to contain tens, hundreds and thousands of spores. The suspensions of all the dilutions were gradually exposed to a microwave radiation power of 170, 510 and 850 W. In all the cases, the exposure time was 1, 2, 3, 4, 5, 10, 15, 20, 25 and 30 minutes. After cooling, 0.1 ml of each exposed suspension was inoculated onto three modified MYP (mannitol egg yolk polymyxin) agar plates and incubated aerobically at 37 ± 1 °C for 120 hours. The statistical evaluation of the spore counts decreasing with time was performed with the use of the nonparametric Friedman’s variance test using the Unistat Statistical Package v6.5. The results showed that the rate of devitalisation of the spores is dependent on the microwave oven power consumption, but independent of the number of spores. Using a power consumption of 170, 510 and 850 W, the devitalisation of the spores occurred after 15, 3 and 2 min of exposure, respectively.