[Comparison of broth microdilution and E-test methods for the antifungal susceptibility testing of Candida spp....

The incidence of serious fungal infections, particularly invasive Candida infections exhibit an increasing trend in the last decades since the number of patients receiving immunosuppressive treatment is increasing. This situation eventually results in an increment in resistance to antifungal agents. The aim of this study was to compare the standard broth microdilution (BMD) and E-test methods for antifungal susceptibility testing of Candida species isolated from blood cultures in our hospital, against fluconazole, voriconazole, caspofungin and amphotericin B. A total of 46 Candida strains isolated from the blood cultures by BACTEC 9000 (Becton Dickinson, USA) and identified by conventional techniques and API 20C AUX (BioMerieux, France) during January 2006-December 2007, were included into this study. The identification results of the isolates were as follows: C. albicans (23), C. parapsilosis (10), C. tropicalis (5), C. krusei (3), C. famata (2), C. glabrata (1), C. guilliermondii (1), C. kefyr (1). The antifungal susceptibilities were determined by BMD method described in Clinical and Laboratory Standards Institute M27-A3 document and E-test. Only two isolates (C. albicans and C. globrata) were found to be resistant to fluconazole with E-test but susceptible with BMD. The minimal inhibitory concentration (MIC) values of caspofungin were higher (MIC = 1-2 microg/ml) in C. parapsilosis compared to other Candida species using E-test. Only one C. albicans was resistant to voriconazole by E-test (MIC = 4 microg/ml), but it was susceptible by BMD (MIC = 0.08 microg/ml). Since definite resistance breakpoints do not yet exist for amphotericin B, MIC values were considered for amphotericin B and it was found that all strains had identical low MIC values (< 0.002-0.5). When E-test results were compared with the standard BMD results, MIC values were in agreement 80.4% for fluconazole, 84.7% for amphotericin B, 95.6% for voriconazole and 93.4% for caspofungin. These results indicated that the most frequently isolated Candida species among blood cultures was C. albicans, followed by C. parapsilosis and these isolates had low antifungal resistance rates. When voriconazol and caspofungin susceptibilities were considered, both E-test and BMD susceptibility results were in good aggreement in comparison to fluconazol and amphotericin B. E-test can be considered as a compatible method for the antifungal susceptibility testing of Candida species compared to standard broth microdilution method.