Synergetic antimicrobial effect of chlorin e6 and hydrogen peroxide on multi-species biofilms

Abstract

Antimicrobial photodynamic therapy (aPDT) has been considered as a potential alternative to antibiotics for the treatment of biofilm infections. There is evidence that an additional H₂O₂ enhances the antimicrobial efficacy of aPDT. However, the minimum H₂O₂ concentration to achieve this synergistic effect is unclear. A saliva-derived multi-species biofilm was treated with the photosensitizer chlorin e6 (Ce6, 50 µM), H₂O₂ (0.3, 3.3, 33.3 mM), or their combination for 5 min, followed by no irradiation or irradiation at 15 J (cm²)⁻¹ (λ = 450 nm or 660 nm), with or without oxygen. Biofilm viability and metabolic activity were evaluated. The combination of 33.3 mM H₂O₂ and Ce6-aPDT strongly enhanced antimicrobial efficacy compared with either component alone, irrespective of oxygen availability and irradiation wavelength. In particular, the combination resulted in a 6.6-log colony forming unit (CFU) reduction anaerobically under blue irradiation. This combination is a promising treatment for biofilm infections, especially those thriving in an anaerobic microenvironment.

Keywords:

• Photodynamic therapy
• chlorin e6
• hydrogen peroxide
• biofilm
• oxygen

Acknowledgements

The authors thank Paul W. Bible from the College of Arts and Sciences of Marian University in Indianapolis, Indiana, for language editing.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Research and Development Foundation of the West China Hospital of Stomatology, Sichuan University (No. RD-02-201905).