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

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Abstract
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 (1 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. A total of 10 oral isolates of C. albicans were examined for the presence of the PAFE after 1 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. 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. 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 antimycotic agent in question. Whether such mechanisms operate in vivo needs to be clarified by further studies.