ABSTRACT
Candida albicans is a commensal yeast normally present in small numbers as normal oral flora. In a certain condition, however, the yeast may proliferate and/or become invasive resulting in oral candidiasis such as denture stomatitis, and may even cause life-threatening systemic candidiasis. The present study was undertaken to test whether polyphosphate (polyP), which has been shown to be a strong antibacterial agent against a variety of oral pathogens, has antifungal effect on C. albicans. C. albicans ATCC 90027 was grown in Sabouraud-Dextrose broth with or without polyP. Anti-C. albicans activity of polyPs with various chain lengths was determined by measuring the growth of candidal cells at 540 nm. polyPs with chain length of 3 (polyP3) or higher effectively inhibited the candidal growth when added at the very beginning of the culture, whereas orthophosphate and pyrophosphate failed to do so. At the concentration of 0.05 percent, all the polyPs tested inhibited candidal growth. The effect of polyP65 that showed stronger anti-candidal effect than others at the concentrations tested and of Calgon (hexametapolyphosphate, practical grade) was further examined. The concentration of 0.03 percent was enough for polyP65 and Calgon to suppress candidal growth throughout the 48-h incubation. PolyP65 added to the growing C. albicans at its exponential phase was as much effective in inhibiting the candidal growth as added at the very beginning of the culture. It was found that 93.8 and 96.9 percent of the yeast cells lost their viability when polyP65 was added to growing C. albicans at the concentrations of 0.03 and 0.05 percent, respectively. Intracellular nucleotide release from the candidal cells incubated with polyP65 was only slightly increased and the nucleotide release was not reversed by the addition of divalent metal ions like Mg++ and Ca++. Under the transmission electron microscope, although the majority of growing C. albicans cells appeared to be atypical in their shape in the presence of polyP65, only a small number of the cells were observed to be lysed. The overall results suggest that polyP has a strong fungicidal activity against C. albicans, in which chelation-mediated cell lysis may not play the major role, but other novel mechanisms that possibly affect the viability of the yeast may be involved. Since polyP also has a strong antibacterial effect on oral pathogens, it may well be used for the prevention and treatment of a variety of oral diseases caused by a wide spectrum of microorganisms including C. albicans.