Flow Cytometry Antifungal Susceptibility Testing of Candida Species and Comparison with Etest

Flow cytometric (FCM) susceptibility test as well as Etest were used for determination of the susceptibility of 20 Candida isolates to fluconazole, amphotericin B and ketoconazole. Minimum inhibitory concentrations (MICs) were read by Etest after 24h. Using FCM, 4 hours incubation were needed for azoles (fluconazole and ketoconazole) and only 2hrs for amphotericin B to obtain MICs results comparable to those of Etest. Agreement of sensitivity between the two methods was high for fluconazole and ketoconazole regarding C.albicans (Kappa 0.727 but was much lower for amphotericin B in both C.albicans and C.nonalbicans (Kappa 0.40 0.377 respectively). Concerning MICs, regression analysis demonstrated that MICs from flow cytometry and Etest were positively correlated, (r = 0.8 p 0.01). Our study points out the advantages of the flow cytometry approach in antifungal susceptibility testing of candida species over Etest, since speed remains a major problem, inspite of being expensive. Etest was time consuming, yet it did not need any special equipment, so it could be used in any laboratory. However, more studies are needed to assess values of each technique for routine antifungal susceptibility testing.