Curcumin-Mediated Photodynamic Inactivation of Vibrio parahaemolyticus Biofilms on Stainless Steel: Oxidative Damage and Degradation of Exopolysaccharides

Vibrio parahaemolyticus biofilms on stainless steel surfaces pose a serious threat to food safety. This study investigated the anti-biofilm efficacy and eradication mechanism of curcumin -mediated photodynamic inactivation (PDI) by targeting exopolysaccharides, a key component of extracellular polymeric substances (EPS) within biofilms. Results showed that the PDI treatment with 60 μM curcumin and 9.17 J/cm 2 blue light irradiation eradicated V. parahaemolyticus biofilms by >60% and killed 5.0 log CFU/mL cells. Such robust efficiency was attributed to the fact that the PDI treatment greatly cleaved the glycosidic linkages and reduced molecular weight of exopolysaccharides, consequently destroying the structures of hydrogen-bonding networks. These changes decreased the hydrophobicity, reduced the adhesion work and diminished the interfacial tension of EPS matrix, which caused a profound loss of both cohesive and interfacial stability of the biofilm. As a result, the PDI treatment induced the structural disruption and fragmentation of the biofilm network, which contributed to the above high reductions of biomass and sessile cells. This study elucidates the mechanism of PDI against biofilms by targeting the key component of EPS, thereby providing theoretical guidance for the development of potent PDI.