Higher effectiveness of photoinactivation of bacterial spores, UV resistant vegetative bacteria and mold spores with 222 nm compared to 254 nm wavelength

Eleven selected species of vegetative bacteria, bacteria spores and mold spores were irradiated with different doses of UV radiation of a 222 nm krypton-chloride excimer lamp and a 254 nm mercury lamp under laboratory conditions. Then the inactivation curves were determined. The necessary UV fluences for a respective reduction were higher for the excimer lamp for the tested vegetative bacteria of Bacillus cereus, Arthrobacter nicotinovorans, Staphylococcus aureus and Pseudomonas aeruginosa and slightly higher for the spores of Streptomyces griseus and Clostridium pasteurianum. However, less than 250 Jm 2 UV fluence with 222 nm was sufficient for a 4-log reduction, depending on the species. On the other hand, the UV fluences for the 254 nm mercury lamp were much higher for the bacterial spores of Bacillus cereus, Thermoactinomyces griseus and the bacteria of Deinococcus radiodurans and slightly higher for the mold spores of Aspergillus niger and Penicillium expansum. The results show that especially the germs with a higher UV resistance and those with more effective repair mechanisms can be inactivated more efficiently by the 222 nm excimer lamp. This may be due to the fact that low UV fluence mainly affects radiation sensitive microorganisms by DNA damage whereas at higher UV fluence (various) mechanisms of protein damage can presumably be held responsible for inactivation.