Activities of amphotericin B, fluconazole and Voriconazole against Candida bloodstream isolates determined by broth microdilution and disk diffusion methods

Abstract

Objective: Invasive fungal infections caused by Candida species have increased significantly. Candidemia is not only associated with a mortality, but also extends the duration of hospital stay and increases the cost for medical care. Although, the clinical presentations of the patients with candidemia caused by Candida albicans and non-albicans Candida species are indistinguishable, the susceptibilities to antifungal agents of these species are different. This study presents data on antifungal susceptibility profiles of Candida bloodstream isolates. Method: We tested a total of 90 strains, including 35 strains of Candida albicans, 25 strains of Candida tropicalis, 15 strains of Candida parapsilosis, 8 strains of Candida glabrata, 4 strains of Candida krusei and 3 strains of Candida kefyr. Susceptibility to amphotericin B, fluconazole and voriconazole was determined by Clinical Laboratory Standards Institute broth microdilution method (CLSI M27-A3) using RPMI 1640 as test medium supplemented with 2% glucose and disk diffusion methods were performed according to CLSI M44-A2 using methylene blue (0.5 μg/mL) and glucose (2%) enriched Mueller-Hinton agar. Results: In this study, 87.7%, 82.2% of Candida isolates were susceptible to fluconazole with the broth microdilution method and the disk diffusion method respectively, based on CLSI breakpoints. A further 6.6% were classified as susceptible-dose-dependent (8.5% C. albicans, 4.0% C. tropicalis and 25.0% C. glabrata) and fluconazole resistance was detected in 5.5% of all isolates by microdilution method. Four isolates of these strains were C. krusei (100%) and one strain was C. albicans (2.8%). 12.2% of Candida spp. were classified as susceptible-dose-dependent (17.1% C. albicans, 12.0% C. tropicalis, and 25.0% C. glabrata) and fluconazole resistance was detected in 5.5% of all isolates. Four isolates of these strains were C. krusei (100%) and one strain was C. albicans (2.8%) by disk diffusion method. All isolates were susceptible to amphotericin B and voriconazole using by two methods. Conclusion: Voriconazole and amphotericin B were active in-vitro against yeasts. As antifungal drug resistance may become more frequent, it is increasingly important to evaluate current antifungal susceptibility profiles of fungal pathogens.