In Vitro Amphotericin B Susceptibility of Korean Bloodstream Yeast Isolates Assessed by the CLSI Broth Microdilution Method, Etest, and Minimum Fungicidal Concentration Test

Abstract

Although amphotericin B (AMB) has a wide spectrum of activity that encompasses the majority of yeast isolates, there have been recent reports suggesting that some yeast isolates exhibit decreased susceptibility to AMB. However, in vitro AMB susceptibility of yeast species isolates from blood cultures in Korea has not been fully surveyed. A total of 92 bloodstream yeast isolates from four Korean hospitals, representing 10 Candida species (69 isolates) and 4 non-Candida yeast species (23 isolates) were evaluated. AMB minimum inhibitory concentrations (MICs) were determined by two methods: the CLSI method and Etest. AMB minimum fungicidal concentrations (MFCs) were also determined. For all 92 yeast isolates, the CLSI method generated a restricted range of MICs (0.125 to 4 microgram/mL) with 3.3% exhibiting MICs > or =2 microgram/mL, and the corresponding MFC values ranged from 0.25 to 8 microgram/mL with 26.1% showing MFCs > or =2 microgram/mL. Etest produced the widest distribution of MICs, ranging from 0.03 to 32 microgram/mL. High AMB MICs (> or =0.38 microgram/mL) by Etest was observed in 34.8% of the isolates: Candida krusei (100%), Candida rugosa (100%), Trichosporon asashii (100%), Candida glabrata (82%), and Yarrowia lipolytica (75%). Etest disclosed that all isolates of Candida guilliermondii, Candida lusitaniae, Candida pelliculosa and Kodamaea ohmeri were highly susceptible to AMB (MIC < or =0.19 microgram/mL). Our study showed that Etest may be more useful to discriminate yeast isolates with reduced susceptibility to AMB, and some isolates of less common yeast species from Korea may have decreased AMB susceptibilities.