Enhanced antibacterial and antibiofilm functions of the curcumin-mediated photodynamic inactivation against Listeria monocytogenes

Photodynamic inactivation (PDI) is a promising and effective non-thermal sterilization technology. This study aimed to construct the enhanced antibacterial and anti-biofilm blue light-emitting diode PDI with edible photosensitizer curcumin against Listeria monocytogenes cocktail, and to elucidate its antibacterial mechanism by determining the DNA integrity, protein changes, morphological alteration, virulence gene expression, etc. Results showed that the curcumin-mediated PDI inactivated > 4 Log CFU/mL (> 99.99%) of planktonic cells within 5 min (0.54 J/cm(2)) with 0.2 mu M curcumin, and completely inactivated the pathogen within 5min with 1.0 mu M curcumin. Meanwhile, the PDI treatment negatively changed the architectural structure and markedly reduced the adhesion ability of the biofilms, resulting in a highly efficient eradiation. Antibacterial mechanism analysis indicated that the cytoplasmic DNA and protein not the outer membrane of the L. monocytogenes cells were the vulnerable attacking target for the curcumin-mediated PDI. Furthermore, the PDI treatment significantly down-regulated the expression of the virulence genes (inlA, hlyA and plcA) of L monocytogenes, which would decrease the ability of adhesion, invasion and escape of L. monocytogenes. Therefore, the curcuminmediated PDI is a valid and non-thermal technique in inactivating the planktonic and biofilm pathogens.