Sodium copper chlorophyll mediated photodynamic treatment inactivates Escherichia coli via oxidative damage.

Photodynamic technology (PDT) is an emerging non-thermal processing technique, however, due to a lack of edible photosensitizers, its application to the food industry is limited. To better understand sodium copper chlorophyll (SCC) feasibility as a photosensitizer, we analyzed the effects of PDT-SCC on Escherichia coli O157:H7 inactivation using different lighting times (15, 30, 45, 60, and 75 min), lighting power (30, 60, 90, 120, and 150 W), and SCC concentrations (2, 4, 6, 8, and 10 mM). We showed that bactericidal effects depended on all three parameters, but the most suitable sterilization condition for E. coli occurred at 10 mM SCC, for 60 min at 120 W. We also investigated cell morphology, reactive oxygen species (ROS) production, the activity of three oxidative response enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX)), and ompA, ompF, uvrA, and recA expression. When compared with the control group, PDT-SCC destroyed bacterial morphology, increased ROS production, decreased antioxidant enzyme activity (SOD, CAT, and GPX), down-regulated membrane protein gene expression, including ompA and ompF, and up-regulated the DNA damage-repair related genes, uvrA and recA. Thus, bacterial rupture caused by oxidative damage could be the main mechanism underpinning PDT-SCC action.

Inactivation of Bacillus subtilis by Curcumin-Mediated Photodynamic Technology through Inducing Oxidative Stress Response.

Photodynamic sterilization technology (PDT) is widely used in disease therapy, but its application in the food industry is still at the research stage because of the limitations of food-grade photosensitizers. Curcumin exhibits photosensitivity and is widely used as a food additive for its natural color. This study aimed to determine the effect of curcumin-mediated photodynamic technology (Cur-PDT) on Bacillus subtilis and to elucidate the anti-bacterial mechanism involved. First, the effects of curcumin concentration, duration of light irradiation, light intensity, and incubation time on the inactivation of B. subtilis were analyzed. It was found that Cur-PDT inactivated 100% planktonic cells with 50 µmol/L curcumin in 15 min (120 W). Then, the cell morphology, oxidation state and the expression of membrane structure- and DNA damage-related genes of B. subtilis vegetative cells were investigated under different treatment conditions. The membrane permeability of cells was enhanced and the cell membrane structure was damaged upon treatment with Cur-PDT, which were exacerbated with increases of treatment time and curcumin concentration. Meanwhile, the production of reactive oxygen species increased and the activities of the antioxidant enzymes SOD, GPX, and CAT decreased inside the cells. Furthermore, the Cur-PDT treatment significantly downregulated the mRNA of the membrane protein TasA and upregulated the DNA damage recognition protein UvrA and repair protein RecA of B. subtilis. These results suggested that curcumin-mediated PDT could effectively inactivate B. subtilis by inducing cell redox state imbalance, damaging DNA, and disrupting membrane structures.