Frequency of fks Mutations among Candida glabrata Isolates from a 10-Year Global Collection of Bloodstream Infection Isolates

Abstract

bAmong 119 echinocandin non-wild-type (non-WT) Candida glabrata strains from two global surveys, mutations in fks hot spots (HSs) were detected in 28 (from 7 countries and 8 U.S. states): 24 strains (85.7%) had non-WT MICs for micafungin, 22 (78.6%) for anidulafungin, and 25 (89.3%) for caspofungin. The most common FKS substitutions among non-WT strains were at positions F659 (n ‫؍‬ 7) and S663 (n ‫؍‬ 7). Three isolates displaying WT MIC results had F625Y, L630I, and D632Y substitutions or non-HS mutations. Mutations that have been reported to decrease the echinocandin binding to the 1,3-␤-D-glucan synthase were categorized as resistant by applying the new CLSI breakpoint criteria for all three echinocandins. Candida glabrata is a leading human fungal pathogen that causes life-threatening infections and poses a challenge to antifungal therapeutic options due to its refractory susceptibility to the azole agents and the ability to develop resistance to both azoles and the echinocandins (1, 2). Echinocandin resistance in C. glabrata is usually caused by the acquisition of point mutations in hot spot (HS) regions of the fks gene encoding the 1,3-␤-D-glucan synthase (GS), the target of the echinocandin class (3). Furthermore, it is thought that the haploid nature of C. glabrata makes it particularly adept at acquiring resistance mutations.Due to the spectrum and fungicidal potency against Candida spp., the echinocandin agents (anidulafungin, caspofungin, and micafungin) are recommended as first-line therapy for most patients with invasive candidiasis, followed by de-escalation to fluconazole, as directed by the susceptibility of the infecting organism. Resistance to the systemically active echinocandin and azole antifungal agents is distinctly uncommon among bloodstream infection isolates of C. albicans, C. tropicalis, and C. parapsilosis; however, the emergence of resistance to both classes of antifungal agents is now evident for C. glabrata (4), suggesting that this species requires greater monitoring for resistance. Furthermore, a 10-year study conducted in a single U.S. medical center found that the presence of an elevated caspofungin MIC (Ͼ0.12 g/ml) or micafungin MIC (Ͼ0.06 g/ml) served as a sensitive screen for the presence of clinically significant mutations in the fks gene (2).In the present study, we evaluated all C. glabrata strains collected during two global surveillance programs from 2001 to 2011 that displayed MIC values above the epidemiologic cutoff values (ECVs) or had non-wild-type (non-WT) MICs (5, 6) for one or more of the echinocandins upon initial testing. Isolates were retested by the reference broth microdilution (BMD) method (7,8) and were evaluated for the presence of fks mutations.A total of 119 C. glabrata isolates were selected for analysis and were equally distributed among the two surveillance studies and throughout the years tested. These were all isolates that upon initial testing displayed non-WT MIC values for one or more of the echinocandins (micafungin, 26 isolates with non-WT MI...

Rapid Detection of FKS -Associated Echinocandin Resistance in Candida glabrata

“…In theory, such unresolved susceptible/resistant classification is a concern for directing antifungal therapy. In reality, however, it may be only trivial to the diagnostic value of this FKS genotyping method, because the frequency of T1896A mutationcaused D632E is very low (estimated as Ͻ0.5% of all FKS HS mutations) based on several large-scale epidemiological studies on FKS mutations (6,12,18,19,22,23). Nevertheless, an F625F silent mutation-specific MB probe was designed to address this susceptible/resistant uncertainty.…”

Molecular Characterization and In Vitro Antifungal Susceptibility of Candida Glabrata Clinical Isolates with Reduced Echinocandin Susceptibility and High Level Multi-Azole Resistance

“…Any genetic alteration of the primary structure of the protein will affect the ability of the drug and its analogues to bind and/or inhibit the enzyme function. However, we did not find any amino acid change at the HS 1 region which has previously been associated with drug target modification dependent reduction in echinocandin susceptibility in different Candida species [24,25,34]. The increase in MICs detected after the 2nd isolate and all of the isolates thereafter, could be the cumulative effect of multiple amino acid changes outside the HS1 region.…”

“…In C. glabrata, RES is usually caused by the acquisition of point mutations in HS regions of the fks gene [24,25]. In a recent study of 119 C. glabrata isolates, FKS alterations were detected in 31% of strains with elevated MICs to echinocandins, 28 of the 37 strains had HS substitutions [24]. Other known mechanisms such as efflux and reduced permeation of the drug into the cell appear to play no significant role in conferring RES.…”

“…Investigators have reported the emergence of various Candida species with either reduced echinocandin susceptibility (RES) or echinocandin resistance (ECR) [21][22][23][24][25]. Several studies have shown that the primary mechanism for resistance to the echinocandins appears to be the alteration of glucan synthase, in particular Fks1/Fks2 [22,[26][27][28][29].…”

“…Most of the amino acid mutations on the Fks1p related to RES appear to be confined to two regions of the protein and have been designated 'hot spot' 1 (HS1) and 'hot spot' 2 (HS2), located on the amino terminal and the carboxyl terminal halves of the protein, respectively [30]. In C. glabrata, RES is usually caused by the acquisition of point mutations in HS regions of the fks gene [24,25]. In a recent study of 119 C. glabrata isolates, FKS alterations were detected in 31% of strains with elevated MICs to echinocandins, 28 of the 37 strains had HS substitutions [24].…”