Improved Candida spp. Echinocandin Susceptibility Determination by the Addition of Bovine Serum Albumin (BSA).

GARCIA-EFFRON, GUILLERMO; PARK, STEVEN; PERLIN, DAVID S.

San Francisco (EEUU)

Congreso; 49 th Interscience Conference on Antimicrobial Agents and Chemotherapy; 2009

American Society for Microbiology

Background: Echinocandins disrupt the fungal cell wall integrity by inhibiting the ß-1,3-glucan synthase complex. Studies have shown that echinocandins are highly bound to serum proteins, thus altering their antifungal properties, resulting in improved in vitro discrimination between FKS wild type and mutant Candida spp. isolates.  In a previous study, the addition of 50% serum to the MIC assay can improve the identification of echinocandin-resistant Candida spp.  However, this modification cannot be applied to CLSI M27A3 due to safety and standardization difficulties of serum. We evaluated bovine serum albumin (BSA) as an alternative to serum. Methods: A collection of 60 Candida spp. (C. albicans, C. glabrata, C. tropicalis, C. krusei and C. parapsilosis) that included 34 FKS mutants was used in this study.  Echinocandin susceptibility testing was performed following CLSI method M27-A3 with or without 50% serum or BSA. ß-1,3-glucan synthase complexes were isolated and the activity of the echinocandins against the purified proteins was assessed by a polymerization assay in the presence of 50% serum or BSA. A sigmoidal response curve was used to determine the 50% inhibitory concentration (IC50) values for ß-1,3-glucan synthase complex inhibition. Results: Increased MICs (2- to 16-fold) and IC50s (5- to 20-fold) to echinocandins were found with all the strains in the presence of 50% serum. Similar increases in MICs and IC50s were also observed with 50 mg/ml BSA.  Interestingly, 4/17 of the C. glabrata isolates used in this study were unable to grow in the presence of serum, this was not observed with BSA. Conclusion: The use of BSA in echinocandin susceptibility testing can better discriminate between resistant and susceptible Candida spp. isolates as previously demonstrated with 50% serum. Highly standardized BSA avoids the safety disadvantages of serum and can be used in modifying the CLSI document. Furthermore BSA does not inhibit the growth of C. glabrata as seen with serum in some of the strains tested.