Photodynamic and peptide-based strategy to inhibit Gram-positive bacterial biofilm formation

Abstract

The self-produced extracellular polymeric matrix of biofilms renders them difficult to eliminate once they are established. This makes the inhibition of biofilm formation key to successful treatment of biofilm infection. Antimicrobial photodynamic therapy (aPDT) and antimicrobial peptides offer a new approach as antibiofilm strategies. In this study sub-lethal doses of aPDT (with chlorin-e6 (Ce6-PDT) or methylene blue (MB-PDT)) and the peptides AU (aurein 1.2 monomer) or (AU)₂K (aurein 1.2 C-terminal dimer) were combined to evaluate their ability to prevent biofilm development by Enterococcus faecalis. Biofilm formation was assessed by resazurin reduction, confocal microscopy, and infrared spectroscopy. All treatments successfully prevented biofilm development. The (AU)₂K dimer had a stronger effect, both alone and combined with aPDT, while the monomer AU had significant activity when combined with Ce6-PDT. Additionally, it is shown that the peptides bind to the lipoteichoic acid of the E. faecalis cell wall, pointing to a possible key mechanism of biofilm inhibition.

Keywords:

• Antimicrobial photodynamic therapy
• antimicrobial peptides
• biofilms
• Enterococcus faecalis
• lipoteichoic acid

Acknowledgements

The authors thank Dr Wade J. Sigurdson from the Confocal Microscope and Flow Cytometry Facility at the University at Buffalo (SUNY, Buffalo, NY, USA) for support during the acquisition of confocal images.

Disclosure statement

The authors declare no competing interests.

Additional information

Funding

The authors thank the Sao Paulo Research Foundation for their financial support [process numbers 2014/24581-5, 2016/18378-8 and 2018/23015-7 Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP] and the School of Pharmaceutical Sciences – UNESP for infrastructure and additional financial support.