Candidacidal activities of zinc compounds based on incubation time, pH, and ionic strength - An in vitro study

Given the antifungal activity of zinc compounds against Candida albicans, this study aimed to investigate the effects of incubation time, pH, and ionic strength on their candidacidal activity against C. albicans.

Two zinc compounds (zinc chloride and sulfate) and three C. albicans strains (ATCC 10231, 11006, and 18804) were used. The parameters considered include incubation times of immediate, 10, 60, and 120 min, pH of 5.5, 5.0, 4.5, and 4.0, and ionic strength of mimicking human saliva, 100, 150, and 200 mM. The candidacidal activity was determined by comparing colony numbers on the experimental and control plates.

The candidacidal activities of the zinc compounds significantly increased with increasing incubation time, decreasing pH, and increasing ionic strength. Significant levels of candidacidal activity were detected even within 10 min of incubation. The zinc compounds provided additional candidacidal activity under each pH and ionic strength condition. However, the effects of adding zinc compounds were less than those of lowering pH or increasing ionic strength. The candidacidal activities at each incubation time, pH, and ionic strength varied depending on the zinc compound and C. albicans strain; lower activities in zinc chloride and the 18804 strain.

The candidacidal activity of the zinc compounds occurred immediately. They provided additional candidacidal activities even at low pH or high ionic strength environments. Oral healthcare products containing zinc compounds can provide antifungal activities in a changing oral environment.