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 24 hours. Using FCM, 4 hours incubation were needed for azoles [fluconazole and ketoconazole] and only 2 hours 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 and 0.377, respectively]. Concerning MICs, regression analysis demonstrated that MICs from flow cytometry and Etest were positively correlated. This 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, in spite 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

Susceptibility testing of candida for fluconazole by Etest, fungitest and Broth Micro-dilution method

Three methods for fluconazole susceptibility testing of 120 isolates of Candida [54 C. albicans, 36 C. tropicalis, 12 C. krusei, 12 C. glabrata and 6 C. parapsilosis] were compared; namely the Broth Micro-dilution adaptation of the NCCLS method, the Pluconazole Etest, and the Fungitest system. The results of both Etest [read at 24 hours of incubation] and Fungitest were not statistically different and were found to be comparable to the standardized Broth-Micro dilution method. The agreement between the 24-hour Etest reading and the standard broth Micro-dilution method used for fluconazole susceptibility testing of Candida spp. as a whole was excellent [81%] and it ranged between fair to good [66%] for C. krusie and excellent 83%, 86%, and 100% for Candida albicans, C. tropicalis and C. glabrata respectively. The 48-hour Etest reading agreement with the reference Micro-dilution method was fair to good [55%] for all Candida spp. collectively as well as for C. albicans, but poor for C. tropicalis [30%] and C. glabrata [38%]. Major discrepancy was found only in one case [0.83%] and minor discrepancies were found in 9 cases [7.5%] by 24-hour Etest, while by 48-hour Etest, major discrepancies were found in 9 [7.5%] cases and minor discrepancies in 15 [12.5%] cases. Fungitest agreement studies with the standard test showed excellent agreement for C spp. as a whole and for C. albicans [79% and 76%] and fair to good agreement for C. tropicalis [73%]. Regarding Fungitest, major discrepancies were found in 4 cases [3.33%] and minor discrepancies were found in 11 cases [9.16%]. Etest and Fungitest are promising alternatives to the NCCLS reference methods for fluconazole susceptibility testing of Candida yet, further development is necessary to standardize their media, incubation conditions, and test procedures before their introduction as routine methods in the clinical microbiology laboratory