Amphotericin B susceptibility testing of Candida lusitaniae isolates by flow cytofluorometry: comparison with the Etest and the NCCLS broth macrodilution method

A flow cytofluorometric susceptibility test (FCST) was used for rapid deter mination of the susceptibility of Candida lusitaniae isolates to amphoteric in B. The test is based on the decrease in fluorescence intensity of cells stained with 3,3'-dipentyloxacarbocyanine iodide (DiOC(5)(3)), a membrane p otential-sensitive cationic dye, after drug treatment. A total of 58 C. lus itaniae clinical isolates including strains known to be amphotericin B-resi stant on the basis of in-vivo and/or in-vitro data were tested. MICs were d etermined concurrently by the NCCLS broth macrodilution method and the Etes t, both with antibiotic medium 3. Regression analysis demonstrated that the data from the FCST and the Etest were better correlated (r = 0.93, n = 59, P < 0.001) than those from the FCST and the NCCLS method (r = 0.63, n = 59 , P < 0.001). The FCST readily identified a series of putatively susceptibl e and resistant isolates. Our study points out the advantages of the flow c ytometry approach in antifungal susceptibility testing of yeasts, since spe ed remains a major problem in conventional tests.