Intrinsic reduced susceptibility of Candida parapsilosis, Candida orthopsilosis and Candida metapsilosis is due to a single naturally occurring polymorphism in FKS1.

GARCIA-EFFRON, GUILLERMO; KATIYAR, SANTOSH K.; PARK, STEVEN; EDLIND, THOMAS D.; PERLIN, DAVID S.

Jersey city (EEUU)

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

Background: Candida parapsilosis emerged as a common cause of invasive fungal infection. Recently two C. parapsilosis related species has been identified C. orthopsilosis and C. metapsilosis. All three species showed higher echinocandin drugs (ECD) MIC values. It was suggested that a mutation in FKS1p could be the responsible for this phenotype. Despite its epidemiological importance and the therapeutic implications of a reduced ECD susceptibility, the mechanism of this intrinsic ECD resistance has never been elucidated. Methods: Fifteen strains were used (3 C. parapsilosis, 2 C. metapsilosis, 2 C. orthopsilosis, 4 C. albicans - 3 wild type and 1 P649H mutant strains - , 2 C. glabrata - 1 wt and 1 P667T mutant strains). Moreover 1 S. cerevisiae strain harboring the FKS1p P647A mutation was obtained by site directed mutagenesis. FKS genes were amplified and sequenced. Glucan Synthase (GS) was isolated from each strain by product entrapment and ECD activity was assessed by glucan polymerization assay. The kinetic properties of the GS were also studied using Lineweaver-Burk plots (Vmax and Km) and Dixon plottings (Ki). Results: The GS titration curves showed equivalent pattern of increase in Ki values for the C. parapsilosis and it related species than for C. albicans and C. glabrata strains harboring the equivalent mutation. Moreover this mutation confers the equivalent GS kinetic variations (Vmax reduction) in these different Candida species (Vmax: 6.07 nmol.min-1 on average for the wild type strains and 1.16 nmol.min-1 for mutants). Furthermore in S. cerevisiae mutant GS enzyme shows 100-fold increases in Ki values, comparable to those obtained for C. parapsilosis, C. orthopsilosis and C. metapsilosis. Conclusion: The FKS1 Hot Spot 1 C-terminus aa. (660A) is necessary and sufficient to confer ECD resistance in C. parapsilosis, C. orthopsilosis  and C. metapsilosis.