Photodynamic inactivation of Escherichia coli by curcumin in combination with ε-poly-L-lysine

Curcumin-mediated photodynamic inactivation (PDI) has recently garnered significant attention as a novel sterilization technique. However, its efficacy still requires enhancement. This study focuses on the inactivation efficiency and mechanism of curcumin-mediated PDI enhanced by ε-poly-L-lysine (ε-PL) against Escherichia coli . Under 405 nm blue light (BL) irradiation (200 mW/cm 2 ), the combination of ε-PL (38 mg/L) and Cur (300 μM) achieved remarkable bactericidal effects, with >3 log and >7 log reductions in viable cells within 20 and 30 minutes, respectively. The most severe damage to cell morphology and ultrastructure was visualized in (Cur&ε-PL)-LED group using scanning electron microscopy, indicating extensive cell membrane disruption, structural disintegration, and decrease in cell size. As a result, the enhancement of the interaction between targeted cells and photosensitizers triggered the enormous production of intracellular reactive oxygen species (ROS) upon exposure to BL light. The mentioned ROS not only effectively reduced bacterial adhesive capacity, disturbed the membrane potential, but also destructed cell membranes and altered the membrane compositions, which were accountable for the synergistic effect on E. coli cells augmented by ε-PL. These findings provided a crucial theoretical foundation for their potential use in food matrix by elucidating the manner of antibacterial action of the combination of curcumin and a cationic antimicrobial compound. • ε-PL and curcumin was used as photosensitizers to against Escherichia coli • ε-PL significantly enhanced the PDI effect of curcumin especially under irradiation • ε-PL-potentiated mechanism involves in the increase of curcumin uptake and enormous ROS generation