Curcumin-mediated photodynamic inactivation (PDI) against DH5α contaminated in oysters and cellular toxicological evaluation of PDI-treated oysters.

Abstract

The objective of this study was to evaluate the bactericidal effect of curcumin (CUR)-mediated photodynamic inactivation (PDI) against Escherichia coli DH5α in vitro and in oysters, then further investigate the edible security of PDI-treated oysters based on cellular toxicological methods. First, DH5α cells were irradiated by a 470 nm LED light source with an energy density of 3.6 J/cm2. Colony forming units (CFU) were counted and the viability of DH5α cells was calculated after treatment with CUR-mediated PDI. Intracellular production of reactive oxygen species (ROS) was studied by measuring the fluorescence of 2, 7-dichlorofluorescein (DCF) using a flow cytometry. Membrane permeability was measured using confocal laser scanning microscopy (CLSM) with propidium iodide (PI) staining. After that, the bactericidal effect of CUR-mediated PDI was evaluated in oysters which were pre-contaminated with DH5α cells. Finally, cellular toxicology of PDI-treated oysters was evaluated through morphological observation, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, DNA ladder assay, and nuclear staining. Results showed that the viability of DH5α was significantly decreased in a CUR concentration-dependent manner and resulted in an approximately 3.5-log reduction at the concentration of 20 μM. After treatment with CUR-mediated PDI (20 μM, 3.6 J/cm2), the ROS level in DH5α cells and the membrane permeability markedly increased. Our data demonstrated that CUR-mediated PDI had a good decontamination effect against DH5α contaminated in oysters. After incubation with PDI-treated oysters, fibroblasts L929 cell morphology, MTT absorbance and cell apoptosis had no obvious changes. Our findings preliminarily demonstrated that CUR-mediated PDI-treated oysters had no cytotoxicity to fibroblasts.