Eradication of planktonic Vibrio parahaemolyticus and its sessile biofilm by curcumin-mediated photodynamic inactivation

Vibrio parahaemolyticus is the leading pathogen in seafoods. This study established the efficient blue light-emitting diode (LED) photodynamic inactivation (PDI) to eradicate Vibrio parahaemolyticus and its biofilm with photosensitizer curcumin, and the antibacterial and antibiofilm mechanisms were elucidated by determining the DNA integrity, protein changes, morphological alteration, gene expression levels, chemical composition and structural parameters of biofilm, etc. Results showed that the planktonic V. parahaemolyticus could not be visibly detectable on the medium after the curcumin-mediated PDI treatment with 1.0 mu M curcumin within 5 min (1.14 J/cm(2)), and its biofilm was almost completely eradiated with 20.0 mu M curcumin within 60 min (13.68 J/cm(2)). The cellular wall and proteins of V. parahaemolyticus were the vulnerable target for the PDI treatment. Meanwhile, the PDI efficiently inactivated the living cells, reduced the key chemical composition of extracellular polymeric substance and negatively altered the architectures of biofilm. Furthermore, the PDI treatment downregulated the expression of virulence genes (tdh and toxR) and biofilm formation genes (oxyR, aphA, luxR and opaR) of V. parahaemolyticus, which would impede the bacterial infection, colonization and biofilm formation. The study will enrich our knowledge of the PDI-induced inactivation of V. parahaemolyticus, hence unlock the design of novel PDI technology to eradicate bacteria in food industry.