The postantifungal effect (PAFE) of antimycotics on oral C. albicans isolates and its impact on candidal adhesion

Abstract

OBJECTIVE: Postantifungal effect (PAFE) is defined as the suppression of growth that persists following limited exposure of yeasts to antimycotics and subsequent removal of the drug. As there are no data on the PAFE of oral C albicans isolates the main aim of this investigation was to measure the PAFE of 10 oral isolates of C albicans following limited exposure (I h) to five antifungal drugs, including nystatin which has not been previously used in PAFE assays. A secondary aim of the study was to evaluate the biological significance of PAFE, using a nystatin pre‐exposed isolate of C albicans and observing its adherence to denture acrylic surfaces, during the PAFE period. DESIGN: A total of 10 oral isolates of C albicans were examined for the presence of the PAFE after I h exposure to five antifungal drugs, nystatin, amphotericin B, 5‐fluorocytosine, ketoconazole and fluconazole. PAFE was automatically assessed with the help of a Spectramax machine which utilizes the principle of periodic turbidometric assessment of growth rates at a given temperature over a given period. The data thus collected are automatically processed in a graphic format as a computer printout. The PAFE was determined as the difference in time (h) required for growth of the drug‐free control and the drug‐exposed test cultures to increase to 0.05 absorbance level following removal of the antifungal agent (by repeated washing). The adhesion of the single isolate to denture acrylic following limited exposure to nystatin was assessed by a previously described in vitro adhesion assay. RESULTS: Significant PAFE were observed for nystatin, amphotericin‐B and 5‐fluorocytosine. A marginal PAFE was observed for ketoconazole and little or none for fluconazole. The mean duration of the PAFE of nystatin, amphotericin‐B, 5‐fluorocytosine, ketoconazole and fluconazole were 2.89 (±0.27) h, 2.83 (±0.23) h, 3.18 (±0.31) h, 0.65 (±0.11) h and 0.16 (±0.06) h, respectively. The mean percentage reduction of adhesion of oral C albicans BU47204 to denture acrylic during the PAFE period following exposure to nystatin for 10, 30, 50, 70 and 90 min was 9.12%, 61.73%, 65.99%, 82.16% and 83.14%, respectively. CONCLUSIONS: These in vitro findings imply that even a short period of exposure to antifungals may result in modulation of the growth and the virulent attributes of C albicans, which however is largely dictated by the anti‐mycotic agent in question. Whether such mechanisms operate in vivo needs to be clarified by further studies.

Amphotericin B-Induced in vitro Postantifungal Effect on <b><i>Candida</i></b> Species of Oral Origin

“…There are reports on amphotericin B-induced PAFE on C. albicans , C. tropicalis and C. glabrata species [9,10,11]. However, there are no reports on PAFE elicited by amphotericin B on other Candida species of oral origin.…”

“…The MIC was read independently by two laboratory technicians. C. albicans ATCC 90028 and C. tropicalis ATCC 13803 were used as reference strains, as done in previous studies [6,9,10,11]. All experiments were repeated on 2 separate occasions with duplicate determinations on each occasion.…”

“…As in previous PAFE studies [9,10,11], amphotericin B (Sigma, St. Louis, Mo., USA) was dissolved in dimethylsulphoxide and absolute ethanol (3:2 ratio), respectively, and prepared initially as 10,000-µg solutions and stored at –20°C before use. It was thereafter suspended in the following medium during the exposure period (1 h) of yeasts: RPMI 1640 medium, buffered with 0.165 M morpholinopropanesulphonic acid containing L -glutamine and lacking sodium bicarbonate (Sigma, USA), in 1 litre of sterile distilled water, adjusted to a pH of 7.2 and filter sterilized [9,10,11].…”

“…It was thereafter suspended in the following medium during the exposure period (1 h) of yeasts: RPMI 1640 medium, buffered with 0.165 M morpholinopropanesulphonic acid containing L -glutamine and lacking sodium bicarbonate (Sigma, USA), in 1 litre of sterile distilled water, adjusted to a pH of 7.2 and filter sterilized [9,10,11]. This liquid RPMI was stored at 2–8°C.…”

“…The MIC values of amphotericin B were determined by the broth dilution technique [6,9] by performing twofold serial dilutions of the drug in microtitre plates using an inoculum of 1–5 × 10 5 colony-forming units/ml. The MIC was determined visually and spectrophotometrically at 595 nm following 24 h of incubation at 37°C.…”