Site-Directed Mutagenesis of the 1,3-β-Glucan Synthase Catalytic Subunit of and Susceptibility Assays Suggest Its Sensitivity to Caspofungin.

The echinocandin caspofungin inhibits the catalytic subunit Gsc1 of the enzymatic complex synthesizing 1,3-β-glucan, an essential compound of the fungal wall. Studies with rodents showed that caspofungin is effective against asci. However, its efficacy against asci of , the species infecting exclusively humans, remains controversial. The aim of this study was to assess the sensitivity to caspofungin of the Gsc1 subunit, as well as of those of and infecting, respectively, rats and mice. In the absence of an established culture method for species, we used functional complementation of the gsc1 deletant. In the fungal pathogen , mutations leading to amino acid substitutions in Gsc1 confer resistance to caspofungin. We introduced the corresponding mutations into the genes using site-directed mutagenesis. In spot dilution tests, the sensitivity to caspofungin of the complemented strains decreased with the number of mutations introduced, suggesting that the wild-type enzymes are sensitive. The MICs of caspofungin determined by Etest and YeastOne for strains complemented with enzymes (respectively, 0.125 and 0.12 μg/ml) were identical to those upon complementation with the enzyme of , for which caspofungin presents low MICs. However, they were lower than the MICs upon complementation with the enzyme of the resistant species (0.19 and 0.25 μg/ml). Sensitivity levels of Gsc1 enzymes of the three species were similar. Our results suggest that is sensitive to caspofungin during infections, as are and .