The kinetics of Bacillus subtilis spore inactivation on filter paper by u.v. light and u.v. light in combination with hydrogen peroxide

Inactivation of spores of Bacillus subtilis (ATCC 6633) on two different grades of cellulose filter paper (Whatman Grades 2 and 6), by ultraviolet light (u.v.), at an intensity of approximately 4·5 Wm−2 and at fluences of up to 2 × 103 Jm−2, and u.v. in the presence of hydrogen peroxide, is described in terms of multi‐target and single hit–single target kinetic expressions. Wet spores were inactivated at rates ranging from 6·7 to 10·6 higher than that of dry spores on both grades of filter paper. In addition, spore inactivation was up to 5·6 times more rapid on Grade 2 filter paper. Synergistic inactivation was seen to occur when spores were irradiated in the presence of 1% (w/v) hydrogen peroxide with rates up to 5·3 times higher than with treatment solely by u.v. The results obtained are discussed in general terms with particular reference to surface characteristics which might provide shielding to micro‐organisms from incident u.v. light.