Abstract
Treatment of mucocutaneous and cutaneous Candida albicans infections with photosensitizing agents and light, termed photodynamic therapy (PDT), offers an alternative to conventional treatments. Initial studies using the clinically approved photosensitizer Photofrin demonstrated the susceptibility of C. albicans to its photodynamic effects. In the present study, we have further refined parameters for Photofrin-mediated photodynamic action against C. albicans and examined whether mechanisms commonly used by microorganisms to subvert either antimicrobial oxidative defenses or antimicrobial therapy, including biofilm formation, were operative. In buffer and defined medium, germ tubes preloaded with Photofrin retained their photosensitivity for up to 2 hours, indicating the absence of degradation or export of Photofrin by the organism. The addition of serum resulted in a gradual loss of photosensitivity over 2 hours. In contrast to an adaptive response by germ tubes to oxidative stress by hydrogen peroxide, there was no adaptive response to singlet oxygen-mediated stress by photodynamic action. C. albicans biofilms were sensitive to Photofrin-mediated phototoxicity in a dose-dependent manner. Finally, the metabolic activity of C. albicans biofilms following photodynamic insult was significantly lower than that of biofilms treated with amphotericin B for the same time period. These results demonstrate that several of the mechanisms microorganisms use to subvert either antimicrobial oxidative defenses or antimicrobial therapy are apparently not operative during Photofrin-mediated photodynamic treatment of C. albicans. These observations provide support and rationale for the continued investigation of PDT as an adjunctive, or possibly alternative, mode of therapy against cutaneous and mucocutaneous candidiasis.
Highlights
The fungus Candida albicans commonly colonizes the epithelial surfaces of the body, with the oropharyngeal cavity and the vaginal tract as primary sites of mucosal colonization [4]
These results demonstrate that several of the mechanisms microorganisms use to subvert either antimicrobial oxidative defenses or antimicrobial therapy are apparently not operative during Photofrin-mediated photodynamic treatment of C. albicans
We defined conditions of photodynamic treatment that resulted in significant phototoxicity to C. albicans while reducing the time of exposure of the organism to Photofrin, minimizing the concentration of Photofrin needed, and minimizing the fluence of irradiation applied to the organism
Summary
The fungus Candida albicans commonly colonizes the epithelial surfaces of the body, with the oropharyngeal cavity and the vaginal tract as primary sites of mucosal colonization [4]. C. albicans grows as a biofilm on epithelial surfaces [10, 20] and prosthetic devices [23, 34], contributing to the failure of antifungal therapy and recurrent infection. Treatment of superficial C. albicans infections with photosensitizing agents and light, termed photodynamic therapy (PDT), offers an alternative to conventional treatments [8, 9]. Initial studies [3] using Photofrin demonstrated the susceptibility of C. albicans to its photodynamic effects. We have further refined parameters for Photofrin-mediated photodynamic action against C. albicans and examined whether mechanisms commonly used by microorganisms to subvert either antimicrobial oxidative defenses or antimicrobial therapy, including biofilm formation, were operative
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