Rate ofFKSMutations among Consecutive Candida Isolates Causing Bloodstream Infection

Abstract

ABSTRACTPreciseFKSmutation rates amongCandidaspecies are undefined because studies have not systematically screened consecutive, disease-causing isolates. The Sensititre YeastOne (SYO) assay measures echinocandin MICs againstCandidawith less variability than reference broth microdilution methods. However, clinical breakpoint MICs may overstate caspofungin nonsusceptibility compared to other agents. Our objectives were to determineCandidaFKSmutation rates by studying consecutive bloodstream isolates and to determine if discrepant susceptibility results were associated withFKSmutations.FKShot spots were sequenced in echinocandin-intermediate and -resistant isolates and those from patients with breakthrough candidemia or ≥3 days of prior echinocandin exposure. Overall, 453 isolates from 384 patients underwent susceptibility testing; 16% were echinocandin intermediate or resistant. Intermediate susceptibility rates were higher forCandida glabratathan for other species (P< 0.0001) and higher for caspofungin than for other agents (P< 0.0001). Resistance rates were similar between agents.FKSmutations were detected in 5% of sequenced isolates and 2% of isolates overall. Corresponding rates amongC. glabrataisolates were 8% and 4%, respectively. AmongCandida albicansisolates, rates were 5% and <1%, respectively. Mutations occurred exclusively with prior echinocandin exposure and were not detected in other species. Isolates with discrepant susceptibility results did not harborFKSmutations. Mutation rates among isolates resistant to ≥2, 1, and 0 agents were 75%, 13%, and 0%, respectively. In conclusion,FKSmutations were uncommon among non-C. glabrataspecies, even with prior echinocandin exposure. Discrepancies in echinocandin susceptibility by SYO testing were not driven by mutations and likely reflect imprecise caspofungin clinical breakpoints.