The effect of limited exposure to antifungal agents on the germ tube formation of oral Candida albicans

Abstract

Candidal adherence has been implicated as the first step in the pathogenesis of oral candidosis, and germ tube formation by Candida albicans has been attributed as a co-factor that promotes adherence. Oral candidosis is treated with polyenes and the azole group of antifungal agents. As the intraoral concentrations of antifungals fluctuate considerably due to the dynamics of the oral cavity, we investigated the effect of short exposure to sub-lethal concentrations of antifungals on the germ tube formation of Candida albicans. After determining the minimum inhibitory concentration (MIC) of the antifungal agents, ten oral isolates of Candida albicans were exposed to sub-lethal concentrations of nystatin (6xMIC), amphotericin B (8xMIC), 5-fluorocytosine (8xMIC), ketoconazole (4xMIC) and fluconazole (4xMIC), for 1 h. Following removal of the antifungal agent and subsequent incubation in a germ tube-inducing medium, the germ tube formation of these isolates was quantified. When compared with the controls, exposure to nystatin and amphotericin B almost completely inhibited germ tube formation of all the isolates (mean percentage reduction of 97.68 and 97.52%, respectively; P<0.0001), while ketoconazole suppressed this activity to a lesser degree (30.84%; P=0.0174). However, 5-fluorocytosine- and fluconazole-mediated germ tube suppression was minimal (12.63 and 15.93%, respectively; P=0.3255 and P=0.3791). In clinical terms, these findings indicate that short exposure to sub-therapeutic levels of commonly prescribed antifungals may modulate candidal germ tube formation, and thereby the clearance of the organisms from the oral cavity.