Echinocandin susceptibility testing of Candida spp. using the EUCAST EDef 7.1 and CLSI M27-A3 standard procedures: Analysis of the influence of Bovine Serum Albumin Supplementation, Storage Time and Drug Lots.

ARENDRUP, MAIKEN CAVLING; RODR¨ªGUEZ-TUDELA, JUAN LUIS; PARK, STEVEN; GARCIA, GUILLERMO; DELMAS, GUILLAUME; CUENCA-ESTRELLA, MANUEL; GÓMEZ-LÓPEZ, ALICIA; PELIN, DAVID S.

ANTIMICROBIAL AGENTS AND CHEMOTHERAPY

AMER SOC MICROBIOLOGY

Lugar: Washington (EEUU); Año: 2011 vol. 55 p. 1580 - 1587

0066-4804

The MICs of the echinocandins against Candida isolates with fks mutations are higher than those of wild type (WT) isolates. However, the MIC ranges of susceptible and mutant populations overlap or are poorly separated. It was recently reported that a greater separation could be achieved in the presence of serum. To more fully explore this possibility, we compared the performance of the reference microdilution methods using standard and bovine serum albumin (BSA) supplemented growth medium. Anidulafungin, caspofungin and micafungin MICs were determined according to the EUCAST and CLSI methods and with 50% BSA in the medium for 93 clinical isolates (no./no. of mutants): C. albicans (20/10), C. glabrata (19/10), C. dubliniensis (2/1), C. krusei (16/3), C. parapsilosis (19), and C. tropicalis (19/4). Stability of the plates was tested after storage at -80¡ãC for two and six months, respectively, and performance of two different lots of caspofungin was investigated. The addition of BSA to the medium resulted in higher MICs (1-9 2-fold dilution steps) for all isolates and compounds. The increase was greatest for anidulafungin and micafungin, and among WT isolates for C. parapsilosis. The number of very major errors (VME) was reduced (24% (20/84) vs. ¡Ü7% (6/84)) using BSA supplemented EUCAST medium but not for the CLSI method (6% vs. 9%). MIC results were unchanged after six months storage of test plates. The two lots of caspofungin yielded identical results. Addition of BSA to the EUCAST medium increases the ability to differentiate between WT isolates and isolates harboring resistance mutations.