Positions and Numbers of FKSMutations in Candida albicansSelectively Influence In Vitroand In VivoSusceptibilities to Echinocandin Treatment

ABSTRACTCandidemia is the fourth most common kind of microbial bloodstream infection, with Candida 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 the FKSglucan 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 of FKS1and FKS2. Here, we show for the first time the caspofungin-mediated in vivoselection of a double mutation within one allele of the FKS1hot spot 1 in a clinical isolate. We created a set of isogenic mutants and used a hematogenous murine model to evaluate the in vivooutcomes of echinocandin treatment. Heterozygous and homozygous double mutations significantly enhance the in vivoresistance of C. albicanscompared with the resistance seen with heterozygous single mutations. The various FKS1hot spot mutations differ in the degree of their MIC increase, substance-dependent in vivoresponse, and impact on virulence. Our results demonstrate that echinocandin EUCAST breakpoint definitions correlate with the in vivoresponse when a standard dosing regimen is used but cannot predict the in vivoresponse after a dose escalation. Moreover, patients colonized by a C. albicansstrain with multiple mutations in FKS1have a higher risk for therapeutic failure.