Antibacterial Effect and Mechanism of Curcumin Mediated Photodynamic Inactivation Combined with Phage on Foodborne Pathogens

Photodynamic inactivation (PDI) is a new environmentally friendly non-thermal sterilization technology that can effectively inactivate foodborne pathogens. To improve the PDI effect, curcumin was used as a photosensitizer and phage was used as the synergist to investigate the antibacterial effects of PDI with different illumination time and curcumin mediated concentration on Shigella sp. and Salmonella sp.. Plate colony count method was used to evaluate the antibacterial effect of curcumin mediated PDI combined with phage under optimal conditions, and the extracellular reactive oxygen species (ROS) production capacity and intracellular DNA leakage were measured by microplate reader. The morphological changes on the bacterial surface were observed by scanning electron microscopy, and the degree of genomic DNA damage was analyzed by agarose gel electrophoresis, further clarifying the antibacterial mechanism of curcumin mediated PDI combined with phage. The results showed that phage significantly improved the antibacterial effect. When the illumination time was 20 min and the mediated concentration of curcumin was 50 μmol/L and 100 μmol/L, curcumin mediated PDI combined with phage reduced viable bacterial counts of Shigella sp. and Salmonella sp. by 2.77 lg (CFU/mL) and 3.64 lg (CFU/mL), respectively. With the increase in PDI-induced extracellular ROS production, the bacterial growth was significantly inhibited due to the wrinkled bacterial surface morphology, cell membrane disruption leading to DNA leakage and significant DNA degradation. Curcumin mediated PDI combined with phage effectively improved the antibacterial effect on Shigella sp. and Salmonella sp. by inducing ROS production and disrupting cell structure. The research aimed to provide some references for the prevention and control of contamination of foodborne pathogens by PDI.