Photoinactivation of Candida albicans by its own endogenous porphyrins

Abstract

The possibility of photoeradicating the prokaryotic microorganism Candida albicans by enhancing its endogenous porphyrin production and accumulation was investigated in this study. Induction of porphyrin synthesis was performed by the addition of delta-aminolevulinic acid (ALA), or its hydrophobic derivative ALA methyl ester (m-ALA). Photoinactivation of C. albicans was performed under blue light (407-420 nm) illumination. A decrease in viability of about 1.6 or 2.1 orders of magnitudes was obtained with a light dose of 36 J/cm(2) for an initial concentration of 100-mg/ml ALA or m-ALA, respectively. Endogenous porphyrins extracted from the cells showed that cultures incubated with m-ALA accumulated a relatively higher amount of endogenous porphyrins than ALA, indicating better transport through the yeast cell barriers. When a combination of miconazole and ketoconazole (antifungal agents) is given at a sub-inhibitory concentration (0.5 microg/ml each) with an inducer, a 2.1 or 3.2 orders of magnitude decrease in viability is caused with ALA or with m-ALA, respectively, upon illumination. Fluorescence intensities of the accumulated porphyrins as demonstrated by FACS indicate that the combination of the two azole drugs and an inducer cause a relatively high amount of endogenous porphyrins. Although the additive action of both azole drugs allow better penetration of the inducer, especially m-ALA photoeradication remained limited because of an acidic pH generated in the presence of the inducer. The acidic pH is probably the cause for the inefficiency of the photodynamic treatment. More hydrophobic inducers than m-ALA and less acidic must be investigated to improve the photodynamic treatment by endogenous-induced porphyrins.