Cold atmospheric plasma degrades methylene blue and shifts bacterial inactivation during photodynamic therapy
Ki Ho Baek1, Joo Young Park1, Ye-Bin Yoon1
1Advanced Bio and Healthcare Materials Research Division, Korea Institute of Materials Science, Changwon, 51508, Republic of Korea.
Abstract:
Photodynamic therapy (PDT) and cold atmospheric plasma can inactivate bacteria via oxidative stress. Here we examined their combined action against Staphylococcus aureus (S. aureus) using methylene blue (MB)-mediated PDT with a red organic light-emitting diode (OLED) and surface dielectric barrier discharge (SDBD). Under individual treatments, S. aureus inactivation by both PDT and SDBD varied with MB concentration and exposure time. In the presence of MB, plasma rapidly degraded MB, and the effect of microbial inactivation was reduced compared with MB-free conditions. When PDT and SDBD were applied simultaneously, bacterial reduction increased from approximately 1.4 log at 10 min to 4.8 log at 20 min, while MB decreased markedly. This suggests that early inactivation was dominated by MB-mediated photodynamic action, whereas later inactivation was sustained by secondary reactive species produced from SDBD after MB depletion. Photolysis modeling suggested that OLED emission did not substantially alter plasma-generated reactive species, supporting a mechanism driven by time-dependent changes in liquid chemistry rather than gas-phase interference. Acute NIH/3T3 screening showed reduced metabolic activity, indicating the need for cytocompatible dose optimization. These results provide a mechanistic basis for time-dependent pathway shifts during combined MB-PDT and SDBD.
Insights
Combining photodynamic therapy (PDT) and cold atmospheric plasma enhances bacterial inactivation. The study reveals a time-dependent shift in mechanisms, moving from photodynamic action to plasma-generated reactive species for improved Staphylococcus aureus killing.
Area of Science:
- Microbiology
- Biophysics
- Biomedical Engineering
Background:
- Photodynamic therapy (PDT) and cold atmospheric plasma (CAP) are antimicrobial strategies utilizing oxidative stress.
- Both PDT and CAP have shown efficacy against bacteria like Staphylococcus aureus (S. aureus).
- Investigating combined PDT and CAP may offer synergistic antimicrobial effects.
Purpose of the Study:
- To examine the combined effects of methylene blue (MB)-mediated PDT and surface dielectric barrier discharge (SDBD) on S. aureus inactivation.
- To elucidate the underlying mechanisms and time-dependent pathway shifts during combined treatment.
- To assess the impact of plasma on MB degradation and vice versa.
Main Methods:
- S. aureus inactivation was assessed using MB-mediated PDT with red organic light-emitting diode (OLED) and SDBD.
- MB concentration, exposure time, and treatment combinations were varied.
- Photolysis modeling was used to analyze reactive species dynamics.
- Cytocompatibility was evaluated using NIH/3T3 cell metabolic activity assays.
Main Results:
- Individual PDT and SDBD treatments showed variable S. aureus inactivation based on MB concentration and time.
- Plasma rapidly degraded MB, reducing inactivation under initial combined conditions.
- Simultaneous PDT and SDBD achieved significant bacterial reduction (1.4 log at 10 min to 4.8 log at 20 min) as MB depleted.
- OLED emission did not significantly alter plasma-generated reactive species, indicating liquid chemistry shifts drive the mechanism.
Conclusions:
- Combined MB-PDT and SDBD exhibit time-dependent antimicrobial efficacy against S. aureus.
- Early inactivation is driven by MB-PDT, while later stages rely on plasma-generated reactive species after MB degradation.
- Optimization of cytocompatibility is necessary for clinical translation, highlighting the potential of this combined approach.
Related Concept Videos
01:26Physical Methods for Controlling Microbial Growth: Radiation and Filtration
01:23Physical Methods for Controlling Microbial Growth: Temperature