Effective photodynamic inactivation of curcumin in combination with ethylenediaminetetraacetic acid against Burkholderia gladioli pathovar cocovenenans.

The challenges presented by the high prevalence and mortality rates of Burkholderia gladioli pathovar cocovenenans (BGPC) in flat rice noodles (FRNs) have not been effectively addressed. Herein, we developed curcumin/ethylenediaminetetraacetic acid (EDTA)-mediated photodynamic treatment (PDT) as a novel antibacterial therapy for BGPC infection in FRNs. Through single-factor experiments and response surface methodology, the optimal processing parameters of PDT for BGPC inactivation were identified as follows: a photosensitizer solution containing 144 μmol/L curcumin and 0.32% (w/v) EDTA, exposure time of 21 min, and illumination at 43,900 lx. After treatment, the colony count of BGPC decreased by 3.02 log CFU/mL. In addition, the concentration of BGPC in flat rice noodle samples spiked with five BGPC isolates decreased by 2.93-3.15 log CFU/g from the initial inoculum concentration of approximately 8 log CFU/g. Moreover, bongkrekic acid production was completely inhibited in a toxin-producing strain after PDT. An in-depth investigation was performed to elucidate the action mechanism of curcumin/EDTA-mediated PDT in inhibiting BGPC. PDT exerts potent antibacterial effects through oxidative stress. PDT generated singlet oxygen to cause disruption of bacterial cell integrity (p < 0.0001) and structural damage of bacterial surfaces (p < 0.0001). Efflux of intracellular macromolecular contents was observed, accompanied by a sharp decline in adenosine triphosphate levels (p < 0.001), which contributed to impaired bacterial energy metabolism. PDT further caused RNA and DNA damage to impair genomic replication by inducing single- and double-strand breaks in the backbone. This oxidative stress induced cascade pathway finally promoted apoptosis and necrosis. In conclusion, curcumin/EDTA-mediated PDT storage can effectively prevent and control BGPC contamination in FRNs.