Evaluation and comparison of the effects of different exogenous photosensitizers under high irradiance blue light on Listeria monocytogenes

Photodynamic inactivation is an innovative antimicrobial treatment that can be enhanced using high-irradiance blue light (HI-BL) in combination with exogenous photosensitizers. Hence, this study compares the effects of four photosensitizers (curcumin, berberine, quercetin, and capsaicin) under HI-BL on Listeria monocytogenes (Lm), including their antimicrobial activity, gene expression regulation, anti-biofilm efficacy, and potential application in smoked salmon. Berberine-mediated HI-BL reduced Lm viability by 2.9 log CFU/mL within 1 min 15 s, corresponding to 25 J/cm². In the biofilm model, Lm was eradicated by 2.0 log CFU/cm², with further improvement to 4 log CFU/cm² within 2 min 30 s (50 J/cm²), indicating significant photosensitivity and photodynamic efficiency of berberine. In the salmon model, the curcumin-mediated HI-BL resulted in Lm reduction rates of 0.7 log CFU/g after 50 J/cm² and 2.0 logs after 100 J/cm². Further photoreduction was observed against the inherent microbiota, resulting in 3.4 and 3.8 log CFU/g to respective doses. Although the effective decontamination, the salmon lightness (L*) increased in a HI-BL dose-dependent manner, becoming visually perceptible after 100 J/cm². Quercetin and capsaicin were less effective in both biofilm and food models. However, quercetin demonstrated promising antimicrobial activity, achieving a 4.5 log CFU/mL reduction after 3 min and 45 s (100 J/cm²). At sub-inhibitory concentrations, the quercetin-mediated HI-BL down-regulated the expression of the motility genes (fliP, flgE) and the regulatory gene degU, which would decrease the Lm ability of adhesion. In contrast, berberine increased the expression of motility genes (fliP, flgE, motA) the most, while curcumin predominantly up-regulated the virulence and stress response gene prfA. This study contributes to a better understanding of the interactions between L.monocytogenes and photosensitizers, and may help advance blue light technology against this pathogen through suitable photosensitizer selection and antimicrobial treatment optimization.