Photodynamic inactivation of microorganisms as an innovative approach to kill mucocutaneous and skin microorganisms

In 2002, the first documented case of a vancomycin-resistant S. aureus strain (MIC>or=32 microg/mL) was reported. Nowadays approximately 20% of S. aureus isolates in Europe are reported as methicillin-resistant. Besides bacteria infections, the emergence of fungal infections has increased considerably due factors such as immunosuppressive medications, broad-spectrum antibiotics, neutropenia and HIV infections. These tremendous effects underline the importance and the urgency to develop new alternative treatment approaches that are effective against infections caused by multi-resistant pathogens. Photodynamic inactivation of microorganisms (PDIM) is considered as a new approach, which utilizes a photoactive dye, oxygen and visible light to generate reactive oxygen species, which damage irreversible the pathogens during illumination. Cutaneous diseases caused by methicillin-resistant S. aureus or by fungal species are ideally suited to the treatment by PDIM for eradicating localized infections and for modulating wound healing due to the ability to deliver photosensitizer and light with topical application. The challenge of PDIM is to find a therapeutic window in vivo where multi-resistant microorganisms can be killed efficiently, thereby not harming the surrounding tissue or disturbing the residual bacteria-flora of the tissue. Different chemical classes of photosensitizers have demonstrate their potential to photoinactive Gram(+), Gram(-) and fungal cells. This review will focus on general photobiological and photochemical aspects of microbial inactivation by the photodynamic effect as well as to summarize the current knowledge about the possible application modalities of PDIM on localized infectious diseases in dermatology.