Sensitivity of Candida albicans Germ Tubes and Biofilms to Photofrin-Mediated Phototoxicity

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.

Susceptibility of Candida albicans to photodynamic therapy in a murine model of oral candidosis

“…[17][18][19][20][21][22][23][24] The results of the present investigation demonstrated significant reduction of CFU/mL of C. albicans from tongues of mice after 400, 500, and 1000 mg/L of Photogem associated with LED light (305 J/cm 2 ) (455 and 630 nm). There is only one report describing a dose-dependent photoeradication of C. albicans in an immunodeficient murine model.…”

“…A dose-dependent inhibition of metabolic activity was observed after treatment of C. albicans strains with Photofrin (0.01 to 10 mg/L) and illumination with a light fluence of 9 J/cm 2 from an Hg arc lamp. 20 Chabrier-Roselló et al 23 also observed a dose-dependent reduction of metabolic activity of C. albicans biofilms mediated by 10 mg/L of Photofrin and with broadbrand illumination by visible light at fluences ranging from 0.9 to 18 J/cm 2 . However, it has been shown that photosensitization of Candida and subsequent susceptibility to PDT can be reduced dramatically by culture conditions, such as the type of culture medium and the presence of albumin.…”

“…are susceptible to photoinactivation. [17][18][19][20][21][22][23][24] Usually, dyes (toluidine blue and methylene blue) and porphyrins are used as PS combined with red laser light. However, light sources with simpler technology and lower cost than lasers, such as light-emitting diodes (LED), have been successfully applied in PDT.…”

Antimicrobial Photodynamic Inactivation Inhibits Candida albicans Virulence Factors and Reduces In Vivo Pathogenicity

“…Besides the known fungicidal activity of APDI (7,11,24), we observed that sublethal photodynamic action had a temporarily fungistatic effect on C. albicans, and the extent of this activity was dependent on the amount of energy delivered to the cell-PS system, even under conditions bellow the photoinactivation threshold. The increase in lag phase observed immediately after APDI suggested that cell growth was arrested.…”

The role of singlet oxygen and oxygen concentration in photodynamic inactivation of bacteria

“…In addition, the generation of singlet oxygen is very sensitive to oxygen concentration, which may play a role in the photodynamic inactivation of bacteria comparable to that in eukaryotic cells (24). The experiments were carried out with Photofrin, one of the most widely used and clinically approved photosensitizers in photodynamic therapy, which also demonstrates antimicrobial efficacy (25)(26)(27).…”