Positions and Numbers ofFKSMutations in Candida albicans Selectively InfluenceIn VitroandIn VivoSusceptibilities to Echinocandin Treatment

Abstract

ABSTRACTCandidemia is the fourth most common kind of microbial bloodstream infection, withCandida albicansbeing the most common causative species. Echinocandins are employed as the first-line treatment for invasive candidiasis until the fungal species is determined and confirmed by clinical diagnosis. Echinocandins block theFKSglucan synthases responsible for embedding β-(1,3)-d-glucan in the cell wall. The increasing use of these drugs has led to the emergence of antifungal resistance, and elevated MICs have been associated with single-residue substitutions in specific hot spot regions ofFKS1andFKS2. Here, we show for the first time the caspofungin-mediatedin vivoselection of a double mutation within one allele of theFKS1hot spot 1 in a clinical isolate. We created a set of isogenic mutants and used a hematogenous murine model to evaluate thein vivooutcomes of echinocandin treatment. Heterozygous and homozygous double mutations significantly enhance thein vivoresistance ofC. albicanscompared with the resistance seen with heterozygous single mutations. The variousFKS1hot spot mutations differ in the degree of their MIC increase, substance-dependentin vivoresponse, and impact on virulence. Our results demonstrate that echinocandin EUCAST breakpoint definitions correlate with thein vivoresponse when a standard dosing regimen is used but cannot predict thein vivoresponse after a dose escalation. Moreover, patients colonized by aC. albicansstrain with multiple mutations inFKS1have a higher risk for therapeutic failure.