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Updated: Mar 19, 2026
An In Vitro Model to Study the Effect of 5-Aminolevulinic Acid-mediated Photodynamic Therapy on Staphylococcus aureus Biofilm
Published on: April 16, 2018
Sub-lethal doses of photodynamic therapy affect biofilm formation ability and metabolic activity of Enterococcus
M Pourhajibagher1, N Chiniforush2, S Shahabi3
1Department of Microbiology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Background:
During photodynamic therapy (PDT) in the treatment of a primary endodontic infection, it is extremely likely that microorganisms would be exposed to sub-lethal doses of PDT (sPDT). Although sPDT cannot kill microorganisms, it can considerably influence microbial virulence. This study was conducted to characterize the effect of sPDT using toluidine blue O (TBO), methylene blue (MB), and indocyanine green (ICG) on biofilm formation ability and metabolic activity of Enterococcus faecalis.
Methods:
The antimetabolic and antibiofilm potential of ICG-, TBO-, and MB-sPDT against E. faecalis was analyzed at sub-lethal doses (1/2-1/64 minimum inhibitory concentration) using the XTT reduction assay, crystal violet assay, and scanning electron microscopy.
Results:
Higher doses of sPDT adversely affected biofilm formation ability and metabolic activity. ICG-, TBO-, and MB-PDT at a maximum sub-lethal dose markedly reduced the formation of biofilm up to 42.8%, 22.6%, and 19.5%, respectively. ICG-, TBO-, and MB-sPDT showed a marked reduction in bacterial metabolic activity by 98%, 94%, and 82%, respectively. ICG-PDT showed a stronger inhibitory effect on biofilm formation in E. faecalis than MB- and TBO-PDT at sub-lethal levels. Interestingly, a gradual increase in metabolic activity and biofilm formation upon exposure to a lower dose of test sPDT were observed.
Conclusion:
sPDT showed dual effect on biofilm formation ability and metabolic activity of E. faecalis. High doses revealed antimetabolic and antibiofilm potential activity, whereas lower doses had conflicting results. Hence, when PDT is prescribed in clinical settings, the dose of PDT used in vivo should be taken into consideration.
Insights
Sub-lethal photodynamic therapy (sPDT) affects Enterococcus faecalis virulence. Higher sPDT doses inhibit biofilm formation and metabolic activity, while lower doses yield conflicting results, impacting clinical PDT applications.
Area of Science:
- Microbiology
- Biomedical Engineering
- Dental Therapeutics
Background:
- Sub-lethal photodynamic therapy (sPDT) may influence microbial virulence during endodontic treatment.
- Enterococcus faecalis is a common pathogen in persistent endodontic infections.
- Understanding sPDT effects on E. faecalis is crucial for optimizing treatment outcomes.
Purpose of the Study:
- To investigate the impact of sPDT using toluidine blue O (TBO), methylene blue (MB), and indocyanine green (ICG) on E. faecalis biofilm formation.
- To characterize the effect of sPDT on the metabolic activity of E. faecalis.
- To evaluate the dose-dependent effects of sPDT on E. faecalis virulence factors.
Main Methods:
- E. faecalis was exposed to sPDT using ICG, TBO, and MB at varying sub-lethal concentrations.
- Biofilm formation was quantified using the crystal violet assay.
- Metabolic activity was assessed via the XTT reduction assay.
- Microbial morphology was visualized using scanning electron microscopy.
Main Results:
- Higher sPDT doses significantly reduced E. faecalis biofilm formation (up to 42.8% with ICG) and metabolic activity (up to 98% with ICG).
- ICG-sPDT demonstrated the most potent antibiofilm and antimetabolic effects.
- Lower sPDT doses paradoxically increased metabolic activity and biofilm formation, indicating a dual dose-dependent effect.
Conclusions:
- sPDT exhibits a dual effect on E. faecalis biofilm formation and metabolic activity.
- High-dose sPDT possesses significant antimetabolic and antibiofilm potential.
- Careful consideration of PDT dosage is essential for effective clinical application in endodontics.
