Assessment of the effect of amphotericin B on the vitality of Candida albicans

The processes involved in cell death are complex, and individual techniques measure specific fractions of the total population. The interaction of Can dida albicans with amphotericin B was measured with fluorescent probes with different cellular affinities. These were used to provide qualitative and quantitative information of physiological parameters which contribute to fu ngal cell viability. SYBR Green I and 5,(6)-carboxyfluorescein were used to assess membrane integrity, and bis-(1,3-dibutylbarbituric acid)trimethine oxonol and 3,3-dihexyloxacarbocyanine iodide were used to evaluate alterati ons in membrane potential. The fluorescent indicators were compared with re plication competency, the conventional indicator of viability, By using the se tools, the evaluation of the response of C. albicans to amphotericin B t ime-kill curves delineated four categories which may represent a continuum between alive and dead. The data showed that replication competency (CFU pe r milliliter) as determined by conventional antifungal susceptibility techn iques provided only an estimate of inhibition. Interpretation of fluorescen t staining characteristics indicated that C. albicans cells which were repl ication incompetent after exposure to greater than 0.5 mu g of amphotericin B per mi still maintained degrees of physiological function.