Method to sensitize bacterial spores to subsequent killing by dry heat or ultraviolet irradiation

Hydrogen peroxide and ultraviolet irradiation are known to interact synergi stically for killing of bacterial spores. Synergy could be demonstrated wit h spores of Bacillus megaterium ATCC19213 adsorbed to filter paper strips o r glass coverslips treated first with the peroxide and then dried for as lo ng as 48 h prior to UV irradiation. This delayed action was considered to b e due to absorption of the peroxide by the spores in an active but not read ily vaporized form, which could become sporicidal also if the spores were h eated to 50 degreesC. B. megaterium spores mixed with 0.1% (32.6 mM) H2O2 s olution appeared to absorb as much as 15 mu mol/mg dry weight or about 0.5 mg/mg, but only a third to half of the peroxide could be recovered by water washing. A part of the unrecovered peroxide was degraded in reactions resu lting in measurable production of oxygen. Degradation was not reduced by he ating the spores to 65 degreesC or by azide and so appeared to be non-enzym atic. Spores of the anaerobe Clostridium sporogenes were also sensitized to ultraviolet killing by H2O2 treatment followed by drying. They appear to a bsorb less peroxide, only about 2 mu mol/mg, but had lower capacities to de grade H2O2 so that nearly all of the peroxide could be recovered by washing with water. The findings presented should be helpful in the design of new methods for synergistic killing of spores by H2O2 and UV irradiation or dry heat, especially involving, for example, packaging materials. (C) 2000 Els evier Science B.V. All rights reserved.