ORIGINAL ARTICLE Inactivation of food pathogen Bacillus cereus by photosensitization in vitro and on the surface of packaging material Z. Luksiene, I. Buchovec and E. Paskeviciute Institute of Applied Research, Vilnius University, Vilnius, Lithuania Introduction Microbiological food safety is an increasing worldwide problem. An estimated 76 million cases of food-borne disease outbreaks occur annually in the United States, costing 6Æ5–34Æ9 billion dollars in medical care and lost productivity (Mead et al. 1999). Clostridium botulinum, Bacillus cereus and Listeria monocytogenes are the main Gram-positive pathogens causing food-borne diseases (Altekruse et al. 1997). Even spore-forming B. cereus has been identified as the cause of 27 000 cases of food-borne illnesses in the United States (Mead et al. 1999). Bacillus cereus is naturally found in soil environments, because it can contaminate wide range of foods: cereals, fresh vegeta- bles, berries and fruits. Additionally, this pathogen was found in ready-to-eat foods and sauces (Rosenquist et al. 2005). Keywords 5-aminolevulinic acid, Bacillus cereus, decontamination technology, inactivation, photosensitization. Correspondence Zivile Luksiene, Institute of Applied Research, Vilnius University, Sauletekio 10, Lt-10223 Vilnius, Lithuania. E-mail: zivile.luksiene@mtmi.vu.lt 2008 ⁄ 1866: received 30 October 2008, revised 20 April 2009 and accepted 3 May 2009 doi:10.1111/j.1365-2672.2009.04383.x Abstract Aims: The study was focused on the possibility to inactivate food pathogen Bacillus cereus by 5-aminolevulinic acid (ALA) – based photosensitization in vitro and after adhesion on the surface of packaging material. Methods and Results: Bacillus cereus was incubated with ALA (3–7Æ5 mmol l )1 ) for 5–60 min in different environment (PBS, packaging material and wheat grains) and afterwards illuminated with visible light. The light source used for illumination emitted light at k = 400 nm with energy density at the position of the cells, 20 mW cm )2 . The illumination time varied from 0 to 20 min, and subsequently a total energy dose was between 0 and 24 J cm )2 . The obtained results indicate that B. cereus after the incubation with 3–7Æ5 mmol l )1 ALA produces suitable amounts of endogenous photosensitizers. Following illumina- tion, micro-organism inactivated even by 6Æ3 log. The inactivation of B. cereus after adhesion on the surface of food packaging by photosensitization reached 4 log. It is important to note that spores of B. cereus were susceptible to this treatment as well; 3Æ7-log inactivation in vitro and 2Æ7-log inactivation on the surface of packaging material were achieved at certain experimental conditions. Conclusions: Vegetative cells and spores of Gram-positive food pathogen B. cereus were effectively inactivated by ALA-based photosensitization in vitro. Moreover, the significant inactivation of B. cereus adhered on the surface of packaging material was observed. It was shown that photosensitization-based inactivation of B. cereus depended on the total light dose (illumination time) as well as on the amount of endogenous porphyrins (initial ALA concentration, time of incubation with ALA). Significance and Impact of the Study: Our previous data, as well as the one obtained in this study, support the idea that photosensitization with its high selectivity, antimicrobial efficiency and nonthermal nature could serve in the future for the development of completely safe, nonthermal surface decontami- nation and food preservation techniques. Journal of Applied Microbiology ISSN 1364-5072 ª 2009 The Authors Journal compilation ª 2009 The Society for Applied Microbiology, Journal of Applied Microbiology 107 (2009) 2037–2046 2037