Inactivation of Bacillus cereus by Na-chlorophyllin-based photosensitization on the surface of packaging

This study was focused on the possibility to inactivate food-borne pathogen Bacillus cereus by Na-chlorophyllin (Na-Chl)-based photosensitization in vitro and after attachment to the surface of packaging material. Bacillus cereus in vitro or attached to the packaging was incubated with Na-Chl (7·5 x 10⁻⁸ to 7·5 x 10⁻⁵ mol l⁻¹) for 2-60 min in phosphate buffer saline. Photosensitization was performed by illuminating cells under a light with a λ of 400 nm and an energy density of 20 mW cm⁻². The illumination time varied 0-5 min and subsequently the total energy dose was 0-6 J cm⁻². The results show that B. cereus vegetative cells in vitro or attached to the surface of packaging after incubation with 7·5 x 10⁻⁷ mol l⁻¹ Na-Chl and following illumination were inactivated by 7 log. The photoinactivation of B. cereus spores in vitro by 4 log required higher (7·5 x 10⁻⁶ mol l⁻¹) Na-Chl concentration. Decontamination of packaging material from attached spores by photosensitization reached 5 log at 7·5 x 10⁻⁵ mol l⁻¹ Na-Chl concentration. Comparative analysis of different packaging decontamination treatments indicates that washing with water can diminish pathogen population on the surface by <1 log, 100 ppm Na-hypochlorite reduces the pathogens about 1·7 log and 200 ppm Na-hypochlorite by 2·2 log. Meanwhile, Na-Chl-based photosensitization reduces bacteria on the surface by 4·2 orders of magnitude. Food-borne pathogen B. cereus could be effectively inactivated (7 log) by Na-Chl-based photosensitization in vitro and on the surface of packaging material. Spores are more resistant than vegetative cells to photosensitization-based inactivation. Comparison of different surface decontamination treatments indicates that Na-Chl-based photosensitization is much more effective antibacterial tool than washing with water or 200 ppm Na-hypochlorite. Our data support the idea that Na-Chl-based photosensitization has great potential for future application as an environment-friendly, nonthermal surface decontamination technique.