Effects of sub-inhibitory concentrations of antifungal agents on adherence of Candida spp. to buccal epithelial cells in vitro

Abstract

The adherence of three Candida spp. to human buccal epithelial cells following treatment of the yeast with subinhibitory concentrations of amphotericin B, nystatin, miconazole nitrate and 5-fluorocytosine was investigated in vitro. Preincubation of C. albicans, C. tropicalis or C. kefyr with these antifungals inhibited their adherence to varying degrees (reduction between 17% and 78% of the control value). Pretreatment of yeast for a short period (1 h) had less effect on adhesion than pretreatment for a long period (24h). Furthermore, treating C. albicans with a combination of amphotericin B plus 5-fluorocytosine, both at 1/8 MIC level, led to stronger adherence inhibition than that obtained for yeast pretreated with either one alone at 1/4 MIC levels. Exposure of C. albicans to antifungals affected the outer cell envelope, as observed by scanning electron microscopy, it also suppressed germination significantly, again to a different extent depending on the antifungal used. Compared with the control grown yeasts, an increase in the excretion of extracellular polymer into the supernatant of yeast cultured with various antifungals was observed. Chemical composition of this material showed that it is mannoprotein in nature containing hexoses (85-90%) and protein (7-9%). Mannose was the major sugar making about 87% of the total carbohydrates. Our results suggest that antifungals, at sub-inhibitory concentrations, have multiple effects on Candida and point to the possibility of using these drugs in the prophylaxis against candidosis.