Chapter 18: Antimicrobial Effects of Photosensitized Silicon Phthalocyanine (Pc) 4

The incidence and prevalence of bacterial and fungal infections will continue to increase because of (i) more frequent use of broad-spectrum antibiotics and antifungals as well as immunosuppressive medications (ii) increased number of invasive medical procedures and (iii) higher incidence of neutropenia and HIV infections. In addition to the adverse side effects, the growing resistance against both antibiotic and antifungal agents has driven the continuing search for alternative treatment modalities. One promising option is photodynamic therapy (PDT). Numerous in vitro studies have clearly demonstrated activity of PDT against viruses, bacteria, yeast-like fungi and dermatophytes, using photosensitizers that include phenothiaziniums, porhyrins and phthalocyanines. Our lab has demonstrated that PDT sensitized by silicon phthalocyanine (Pc) 4 can efficiently induce cell death of Candida albicans, Trichophyton rubrum and Staphylococcus aureus. Because of the mechanism of action of PDT, which involves oxidative damage to cell membranes, microbial killing was observed in all species, regardless of their susceptibility or resistance to standard antimicrobial agents.