Candida species are a major cause of life-threatening bloodstream infections worldwide. Although Candida albicans is responsible for the vast majority of infections, the clinical relevance of other Candida species has also emerged over the last twenty years. This shift might be due in part to changes in clinical guidelines, as echinocandins became the first line of therapeutics for the treatment. Candida parapsilosis is an emerging non-albicans Candida species that exhibits lower susceptibility levels to these drugs. Candida species frequently display resistance to echinocandins, and the mechanism for this is well-known in C. albicans and Candida glabrata, where it is mediated by amino acid substitutions at defined locations of the β-1,3-glucan synthase, Fks1p. In C. parapsilosis isolates, Fks1p harbors an intrinsic amino acid change at position 660 of the hot spot 1 (HS1) region, which is thought to be responsible for the high MIC values. Less is known about acquired substitutions in this species. In this study, we used directed evolution experiments to generate C. parapsilosis strains with acquired resistance to caspofungin, anidulafungin, and micafungin. We showed that cross-resistance was dependent on the type of echinocandin used to generate the evolved strains. During their characterization, all mutant strains showed attenuated virulence in vivo and also displayed alterations in the exposure of inner cell wall components. The evolved strains harbored 251 amino acid changes, including three in the HS1, HS2, and HS3 regions of Fks1p. Altogether, our results demonstrate a direct connection between acquired antifungal resistance and virulence of C. parapsilosis IMPORTANCE Candida parapsilosis is an opportunistic fungal pathogen with the ability to cause infections in immunocompromised patients. Echinocandins are the currently recommended first line of treatment for all Candida species. Resistance of Candida albicans to this drug type is well characterized. C. parapsilosis strains have the lowest in vitro susceptibility to echinocandins; however, patients with such infections typically respond well to echinocandin therapy. There is little knowledge of acquired resistance in C. parapsilosis and its consequences on other characteristics such as virulence properties. In this study, we aimed to dissect how acquired echinocandin resistance influences the pathogenicity of C. parapsilosis and to develop explanations for why echinocandins are clinically effective in the setting of acquired resistance.

This research was supported by GINOP-2.3.2-15-2016-00035 and NKFIH K123952. T.G.’s research group acknowledges support from the Spanish Ministry of Economy, Industry, and Competitiveness (MEIC) for grant BFU2015-67107 cofounded by European Regional Development Fund (ERDF), from the Catalan Research Agency (AGAUR) SGR857, and a grant from the European Union’s Horizon 2020 research and innovation program under grant agreement ERC-2016-724173, the Marie Sklodowska-Curie grant agreement H2020-MSCA-ITN-2014-642095. H.M.M. and N.E.L.-P. are supported by Consejo Nacional de Ciencia y Tecnología (reference PDCPN2014-247109, and FC 2015-02-834), and Universidad de Guanajuato (reference 1025/2016; CIIC 95/2018). L.B. is supported by NKFIH grant K112294.