KCS

Photodynamic inactivation (PDI) of microorganisms is based on the concept that a dye, known as a photosensitizer, should be localized preferentially in the bacteria and not in the surrounding tissues or cells, and subsequently activated by low doses of visible light of an appropriate wavelength to generate free radicals or singlet oxygen that are toxic to target microorganisms.1 Due to the bacterial resistance to current antibiotics, the bacterial photodynamic inactivation has been developed as an alternative approach to antimicrobial drug treatment. To more closely mimic the conditions likely to be experienced in vivo, the photodynamic therapy was carried out on the S. aureus bacterial cells as the most important organism that can cause a range of mild to severe infections in skin and burn wounds2 in the presence of human blood plasma and human serum albumin (HSA), representing a model more comparable to wound fluid. PDI experiments were performed using a LED (40 mW/cm-2) and newly synthesized methyl (pyro)pheophorbide-a, bearing non-aromatic cyclic compound as the photosensitizers. Results indicate that microorganisms could be successfully photoinactivated by tropolone methyl (pyro)pheophorbide-a derivatives when suspended in phosphate buffered saline (PBS), however changing the medium into 4.5% and 7% HSA/PBS solutions reduced the effectiveness of lethal photosensitization of bacteria, showing a significant inhibition of PDI on S.aureus. The same results were obtained with human blood plasma; however reduce in PDI sensitivity has appeared less considerable than HSA solutions. Use of PDI in order to treat the skin/burn wound infections may represent a useful alternative to conventional antimicrobial treatments and thereby may help to reduce the emergence of antibiotic resistance. Although the results of these in vitro studies are promising, in vivo studies are needed to ascertain whether appreciable bacterial kills can be obtained in a wound model.