Electroporation enhances antimicrobial photodynamic therapy mediated by the hydrophobic photosensitizer, hypericin.

The effective transport of photosensitizers (PS) across the membrane and the intracellular accumulation of PS are the most crucial elements in antimicrobial photodynamic therapy (aPDT). However, due to the morphological complexity of Gram-negative bacteria the penetration of PS is limited, especially hydrophobic PS. Electroporation (EP) could increase the effectiveness of aPDT, by promoting the formation of transient pores that enhance the permeability of the bacterial membrane to PS. In this study we evaluated the combination of aPDT mediated by the hydrophobic PS, hypericin and EP (aPDT/EP) against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. These bacteria were exposed to light (590 nm) in the presence of hypericin (4 μM), following electroporation. The results showed that aPDT/EP inactivated 3.67 logs more E. coli and 2.65 logs more S. aureus than aPDT alone. Based on these results we suggest that EP can potentiate the aPDT effect.