Amphotericin B susceptibility of Candida species assessed by rapid flow cytometric membrane potential assay

A method for detection of the susceptibility of Candida species to amphotericin B is described. The technique is a modification of a similar flow cytometric technique designed to detect antibiotic susceptibility of Staphylococcus aureus. Membrane potential changes caused by the antibiotic are measured flow cytometrically by using the fluorescent membrane potential-sensitive dye 3,3'-dipentyloxacarbocyanine iodide. One strain each of C. albicans and C. tropicalis (both sensitive to amphotericin B) and one strain of C. tropicalis (resistant to amphotericin B) were used to validate the method. Sensitivity or resistance was easily determined after 30 min of incubation in the presence of the antibiotic, and the drug effect was evident in a dose-dependent manner.