In vitro antifungal susceptibilities of Candida species to liposomal amphotericin B, determined using CLSI broth microdilution, and amphotericin B deoxycholate, measured using the Etest

The antifungal susceptibilities of 598 isolates of Candida spp. (bloodstream, other sterile sites) to liposomal amphotericin B (L-AmB) versus amphotericin B (AmB) were determined. Minimal inhibitory concentrations (MICs) were calculated using the Clinical and Laboratory Standards Institute broth microdilution (BMD; M27-A3) method for L-AmB and the E-test method for AmB. The MIC50/MIC90 (µg ml-1) values for L-AmB BMD and AmB E-test were 0.25/1 and 0.19/0.5, respectively. The overall essential agreement (± 2 dilutions) was 91.5%, ranging from 37.5% (Candida lusitaniae) to 100% (Candida glabrata and Candida krusei). Categorical agreement (CA) between the two methods was categorized on the basis of previously published breakpoint (susceptible/resistant MIC cut-off of 1 µg ml-1). The overall CA at the 48-h reading was 97.3%, ranging from 72.7% (C. krusei) to 100% (Candida albicans). Major and very major discrepancies occurred in 2.3% and 0.3%, respectively. Spearman's rho was 0.48 (p < 0.0001). These results demonstrate the utility of the AmB E-test as a surrogate marker to predict the sensibility and resistance of Candida species to L-AmB, and thus to support its use in antifungal treatment.