Antibacterial photodynamic therapy using water-soluble formulations of hypericin or mTHPC is effective in inactivation of Staphylococcus aureus

Antibacterial photodynamic treatment (APDT) might prove valuable as an alternative to the application of chemoantibiotics for the treatment of staphylococcal infections. The rapid uptake of the photosensitizing agent into bacteria allows for selective killing of microorganisms whilst sparing the eukaryotic host tissue, but also requires removal of excessive dye after the incubation period. We tested water-soluble formulations of hypericin (PVP-hypericin) and m-tetrahydroxyphenylchlorin (Fospeg (R)), which could be applied as aqueous sprays and removed easily by flushing with buffers, for their efficiency in killing Staphylococcus aureus. For both sensitizers, 100 nM of the photoactive substance incubated for 5 min and illuminated for 30 min at 75 mW cm(-2) lead to a 4-5 log unit reduction in bacterial count. At a concentration of 300 nM (incubation time 5 min), 30 min illumination at 25 mW cm(-2) is more effective than 10 min illumination at 75 mW cm(-2) (both resulting in the same fluence). We suggest both substances as promising candidates for treatment of staphylococcal infections in wounds with APDT.