Inactivation of Bacillus subtilis spores on aluminum and polyethylene preformed cartons by UV-excimer laser irradiation

The efficacy of UV RrF-excimer laser light (at 248 nm) to inactivate Bacill us subtilis spores loaded onto preformed cartons was found to be dependent on the interior carton coating and scheme by which the irradiation was appl ied. When the carton was held static during UV laser treatment, the majorit y of the dose was delivered to the base of the carton and to a lesser exten t to the upper part of the pack. In this arrangement no irradiation of the interior sides of the carton was observed. A more even distribution of dose was achieved, however, by moving the carton within the laser beam during i rradiation treatment. The distribution of UV was also found to be dependent on the type of carton interior coating. With aluminum cartons the dose mea sured was found to be significantly greater (P < 0.01) and more evenly dist ributed across the interior compared to when polyethylene packs were tested . Under optimized conditions no spore survivors were detected on aluminum c artons preloaded with 9.5 x 10(5) B. subtilis spores by applying a UV laser output dose of 160 J. In comparison, the same conditions only achieved a s ignificantly lower (P < 0.01) reduction in spore numbers (log count reducti on 4.2) when polyethylene cartons were used. This difference in lethality a nd UV distribution of laser light was associated with the higher internal r eflection of photons with aluminum cartons. The suitability of UV-excimer l asers for sterilizing preformed cartons over traditional germicidal lamp-ba sed methods is discussed.