Photodynamic inactivation of bacteria to decolonize meticillin-resistant Staphylococcus aureus from human skin

To prevent infections that arise from the skin surface it is necessary to decolonize human skin prior to any proposed treatment or surgical intervention. Photodynamic inactivation of bacteria (PIB) uses cationic photosensitizers that attach to the surface of bacteria, generate reactive oxygen species on light irradiation and thereby kill bacteria via oxidative mechanisms.

To evaluate the potential and the safety of PIB for decolonization of bacteria from skin.

PIB with the new photosensitizer SAPYR [2-((4-pyridinyl)methyl)-1H-phenalen-1-one chloride] was initially tested against different bacterial species in vitro. Then, ex vivo porcine skin samples were used as a model for decolonization of different bacteria species. The numbers of viable bacteria were quantified and the mitochondrial activity of skin cells was histologically analysed (using nitroblue tetrazolium chloride, NBTC). The same procedure was performed for human skin and meticillin-resistant Staphylococcus aureus (MRSA).

The in vitro studies showed a 5 log₁₀ reduction of all tested bacterial species. On ex vivo porcine skin samples, PIB reduced the viability of all tested bacterial species by at least 3 log₁₀ steps. On human skin samples ex vivo, PIB reduced the number of viable MRSA by maximal 4·4 log₁₀ steps (1000 μmol L^-1 SAPYR, incubation time 10 min, 60 J cm^-2 ). NBTC staining showed normal mitochondrial activity in skin cells after all PIB modalities.

The results of this study show that PIB can effectively and safely kill bacteria like MRSA on the skin surface and might have the potential of skin decolonization in vivo.