The effect of glucose and human serum on 5-aminolevulinic acid mediated photodynamic inactivation of Candida albicans

In response to the growing number of life-threatening infections caused by opportunistic Candida albicans fungi we have examined and discussed the effect of glucose and human serum on the efficiency of photosensitization of C. albicans cells with 5-aminolevulinic acid (5-ALA) used as a precursor of protoporphyrin IX (PpIX). We used 630 nm laser diode as an excitation source to enhance the penetration depth and diminish unwanted light scattering, additionally the experiments were performed in planktonic and biofilm cultures to differentiate the results obtained for cells showing various phenotypic characteristics. Based on performed experiments it became obvious that the incubation of C. albicans fungal cells with 5-ALA in the presence of glucose caused a significant increase in concentration of intracellular PpIX, resulting in a higher efficacy of photo-toxic effect. The observed results were rationalized by the role of glucose as an energy source, which supported the active transport of 5-ALA into cells. In contrary to glucose, the presence of human serum caused a significant reduction in PpIX concentration in C. albicans cells with exogenous delivery of 5-ALA, resulting in a less efficient photo-fungicidal effect. In general, the obtained results contributed to the current search for efficient, light activated anti-fungal treatments of high efficiency.