Antifungal drug susceptibility of oral Candida albicans isolates may be associated with apoptotic responses to Amphotericin B.

BACKGROUND: Candida albicans is the important opportunistic fungal pathogens which can cause oral Candidiasis and even more seriously systemic infection. Apoptosis of C. albicans induced by environmental factor such as weak acid and antifungal drugs were studied recently. Illustrating the phenomenon of apoptosis in C. albicans may help us to discover new antifungal therapy by activating the fungal cells to suicide.

METHODS: Two oral C. albians clinical isolates which isolated respectively from healthy host [Strain 23C: minimal inhibition concentration (MIC) is 0.125 microg/ml for Amphotericin B (AmB)] and advanced cancer patient (Strain 28A: MIC is 2 microg/ml for AmB), were induced by 1 microg/ml AmB in vitro for 200 min, and then studied the apoptosis markers using terminal deoxynucletidyltransferase-mediated dUTP nick end labeling (TUNEL) (shown by diaminobenzidine and fluorescent isothiocyanate), and the ultrastructure of cell nuclear using transmission electron microscope (TEM), quantitative analysis using flow cytometry for the rapid exposure of phosphatidylserine at the outer membrane and propodium iodide (PI) double staining. C. albicans conference strain YEM30 was used as the control strain.

RESULTS: With TUNEL assay and TEM, we detected the typical characteristics of apoptosis. Strain 23C (with low MIC) showed significantly higher percentage of apoptosis (19.92%) compared with Strain 28A (with high MIC) which was isolated from the cancer patient (7.29%) (P < 0.01). In addition, 7.3% of early apoptosis cells of Strain 23C can form colonies on the plates, while 15% for Strain 28A. None of the PI+ cells can form colony.

CONCLUSIONS: Apoptosis of oral C. albicans isolates can be induced by AmB. The feature of antifungal drug susceptibility of the oral C. albicans clinical isolates may associate with the response of apoptosis inducing.