Novel FKS Mutations Associated with Echinocandin Resistance in C. glabrata and C. tropicalis.

BONILLA, HECTOR; GARCIA-EFFRON, GUILLERMO; CHUA, DANIEL JOSEPH; TOMADA, JON RUPERT; DIPERSIO, JOSEPH; GHANNOUM, MAHMOUD; PERLIN, DAVID S.

San Francisco (EEUU)

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

American Society for Microbiology

Background: Echinocandins (EC) inhibit fungal cell wall biosynthesis through non-competitive inhibition of ¦Â1,3-D-glucan synthase complex (GS). EC clinical and microbiological resistance is uncommon, but reported with several Candida spp. Clinical failures have been associated more with C. parapsilosis. Mutations in FKS genes that encode subunits of the GS have been implicated in EC resistance in Candida spp. We report on 3 Candida spp. isolates (2 C. glabrata and 1 C. tropicalis) showing clinical and microbiological EC resistance.Methods: Antifungal susceptibility tests were performed following the CLSI M27-A3 document. C. glabrata FKS1 and FKS2 and C. tropicalis FKS1 genes (GenBank accession nos. XM_446406, XM_448401 and EU676168, respectively) were sequenced at the hot spot (HS) regions. GS was isolated by product entrapment and activity was assessed by a glucan polymerization assay. A sigmoidal response curve was used to determine the 50% inhibitory concentration (IC50) values for GS inhibition. C. glabrata ATCC 90030 and C. tropicalis ATCC 750 were used as control strains.Results: DNA sequence analysis of the resistant strains showed that C. tropicalis and one of the C. glabrata strains harbor amino acid substitutions at Fks1p (F641S [C.albicans equivalent] and S629P, respectively) while the other strain showed a S663P change at Fks2p. The mutant isolates showed higher MIC values (¡Ý 16-fold) than wild type strains for all the EC drugs. Moreover, the GS isolated from the mutant strains, showed 25- to >1000-fold higher IC50 values than wild type GSsConclusions: All the EC resistant isolates showed newly described amino acid substitutions in the highly conserved Fksp HS regions linked with elevated MIC and IC50 values. These results reinforce the idea that modification of Fksp at hot spot regions is the common mechanism for EC resistance in Candida spp.