Glucan synthase inhibition helps define clinical susceptibility to echinocandin drugs in Candida albicans and Candida glabrata.

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

Jersey city (EEUU)

Congreso; 9th ASM Conference on Candida and Candidiasis.; 2008

Background: Antifungal susceptibility testing has not breakpoints established for Echinocandin drugs (ED). However the CLSI is considering establishing > or = 2 mg/ml as a breakpoint for ED based on correlation of MIC (M-27 method, 24 hrs, and prominent growth reduction) and independently-assessed outcomes of patients. The objective of this study is to compare the MIC and IC50 values of a collection of C. albicans y C. glabrata ED resistant strains to analyse the suitability of this breakpoint. Methods: A collection of 30 C. glabrata (27 ED Resistant) and 27 C. albicans (21 ED resistant) were studied. MIC values were obtained using the M-27 method (prominent growth reduction) reading at 24 and 48 hrs. FKS genes were amplified and sequenced. Glucan synthase (GS) was isolated by product entrapment and activity was assessed by glucan polymerization assay. IC50 values for GS were determined using a sigmoidal response curve (variable slope). MIC values were compared with IC50s using log2 MIC vs Log10 IC50 plotting (MI plots). Results: 48 % of the C. albicans strains showed a mutation in the FKS1p F641 aa, and 38 % harbour an AA change at the S645 position. On the other hand, substitutions at the S663 position in Fks1p (equivalent to S645 in C. albicans) were the most common mutation founded (33 %) in C. glabrata. C. albicans mutants showed at least 100- fold higher IC50 values for anidulafungin (ANF) and caspofungin (CSF) than wild type strains. Micafungin (MCF) IC50 values were on average 30- fold higher for C. albicans mutants. In C. glabrata, mutant GSs showed 300-fold higher IC50 values for MCF than the wild type strains while ANF and CSF IC50 values were 60-fold higher for mutants. When the C. albicans vs ANF and MCF MI plots were analyzed all the strains with IC50 > 100 ng/ml (100-fold higher than wild types) had an MIC > 0.25 mg/ml. For C. albicans vs CSF all the strains with IC50 > 100 ng/ml showed an MIC > 2 mg/ml. Moreover there were no changes if the MIC was read at 24 hrs or 48 hrs. Conversely, for C. glabrata it can not be established a breakpoint reading the MICs at 24 hrs. For this specie 94% of the mutant strains with MIC > 1 mg/ml showed ANF IC50 values > 10 ng/ml. All the mutant strains showing a CSF MIC > 1 mg/ml had IC50 values > 30 ng/ml, while 85% of the mutants presenting MCF MIC > 0.25 mg/ml showed IC50 values > 10 ng/ml. Conclusion: These analyses support a susceptibility breakpoint for ANF and MCF against C. albicans of > 0.25 mg/ml and a breakpoint of > 2.0 mg/ml for CSF reading the MIC at 24hrs. On the other hand, for C. glabrata these breakpoints could be > 1.0 mg/ml for ANF and CSF but > 0.25 mg/ml for MCF reading the MIC at 48 hrs.