Dual-Stage Blue-Light-Guided Membrane and DNA-Targeted Photodynamic Inactivation Using Octyl Gallate for Ultraefficient Eradication of Planktonic Bacteria and Sessile Biofilms

Abstract

This study aimed to investigate the synergistic bactericidal activity and mechanism of dual-stage light-guided membrane and DNA-targeted photodynamic inactivation (PDI) by the combination of blue light (BL, 420 nm) and the food additive octyl gallate (OG) against Vibrio parahaemolyticus in planktonic and biofilm growth modes. While OG serves as an outstanding exogenous photosensitizer, the planktonic cells were not visibly detectable after the OG-mediated PDI treatment with 0.2 mM OG within 15 min (191.7 J/cm 2 ), and its biofilm was nearly eradicated within 60 min (383.4 J/cm 2 ). Gram-positive Staphylococcus aureus was more susceptible to the PDI than Gram-negative V. parahaemolyticus. The cellular wall and proteins, as well as DNA, were the vulnerable targets for PDI. The membrane integrity could be initially disrupted by OG bearing a hydrophilic head and a hydrophobic tail via transmembrane insertion. The enhancement of OG uptake due to the first-stage light-assisted photochemical internalization (PCI) promoted the accumulation of OG in cells. It further boosted the second-stage light irradiation of the photosensitizer-inducing massive cell death. Upon the second-stage BL irradiation, reactive oxygen species (ROS) generated through the OG-mediated PDI in situ could extensively deconstruct membranes, proteins, and DNA, as well as biofilms, while OG could be activated by BL to carry out photochemical reactions involving the formation of OG−bacterial membrane protein (BMP) covalent conjugates and the interactions with DNA. This dual-stage light-guided subcellular dual-targeted PDI strategy exhibits encouraging effects on the eradication of planktonic bacteria and sessile biofilms, which provides a new insight into the development of an ultraeffective antimicrobial and biofilm removing/reducing technique to improve microbiological safety in the food industry.

Alkyl Gallates as Potential Antibiofilm Agents: A Review

“…Shi et al [ 52 ] investigated the bactericidal and antibiofilm effects of photodynamic inactivation (PDI) against the foodborne pathogen Vibrio parahaemolyticus using the combined action of OG, a food additive, and the application of BL. PDI was used on the pathogen, in both planktonic and biofilm growth forms, to target cell membranes and DNA.…”

Ultraefficient OG-Mediated Photodynamic Inactivation Mechanism for Ablation of Bacteria and Biofilms in Water Augmented by Potassium Iodide under Blue Light Irradiation

“…To observe the three-dimensional (3D) structure of biofilms, samples were collected by confocal laser scanning microscopy (CLSM) (Leica TCS SP8 Scan Head, Germany) with the LIVE/ DEAD Backlight Bacterial Viability Kits (Molecular Probes, Invitrogen, USA). 10 2.5. Eradication of the Mature Biofilm.…”

“…Our previous studies demonstrated that OG could insert into the cell membrane due to its superior affinity toward the membrane, inducing membrane rupture and cellular constituent leakage. 10 Besides, the internalized OG can further interfere with the activity of the ETC on the cytoplasmic membrane and interact with intracellular DNA with the formation of a stable complex. 20 These multitargeted modes of action between OG and biomolecules make OG exert an excellent bactericidal ability regardless of the absence or the presence of oxygen.…”

“…Moreover, OG induced the enhanced uptake and extensive disruption of the cytoplasmic membrane via both "transmembrane insertion" and "PCIlike". 10 II. The formation of ROS.…”

“…In our previous study, we found that gallic acid (GA) and its alkyl esters showed significant killing effects on foodborne microorganisms, of which octyl gallate (OG) displayed superior bacteriostatic activity against foodborne pathogens (Pseudomonas aeruginosa, Escherichia coli, Vibrio parahaemolyticus, Staphylococcus aureus, and Listeria monocytogenes). 10,11 Most recently, to our surprise, OG as a novel photosensitizer under illumination with blue or UVA light at low concentrations endows PDI with intriguing bactericidal efficacy to rapidly eradicate pathogens and nuisance biofilms in a relatively short time due to both photodynamic and intrinsic antibacterial properties of OG itself. 0.15 mM OGmediated PDI with UVA (14.58 J/cm 2 ) exhibited rapid and efficient inactivation of E. coli (>5 Log cfu/mL) within 30 min and complete killing of S. aureus within only 5 min 12 Blue light (420 nm, 210 mW/cm 2 ) and 0.4 mM OG induced high levels of toxic ROS, resulting in a >5 log cfu/mL decrease in the viable cell number of Pseudomonas fluorescens within 15 min.…”