Echinocandin-Induced Microevolution of Candida parapsilosis Influences Virulence and Abiotic Stress Tolerance

Abstract

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.

Triazole Evolution of Candida parapsilosis Results in Cross-Resistance to Other Antifungal Drugs, Influences Stress Responses, and Alters Virulence in an Antifungal Drug-Dependent Manner

“…Previous studies showed that FLU treatment in Galleria mellonella larvae is ineffective against FLU-resistant C. parapsilosis strains (31). This information, together with our results, indicates that adaptation to FLU does not imply a virulence cost in C. parapsilosis, as in the case of echinocandin adaptation (10). In C. glabrata PDR1 (CgPDR1), gain-of-function mutations not only lead to elevated azole MICs but also enhance virulence, indicating that CgPDR1 possibly regulates uncharacterized virulence factors (32).…”

“…Next, we generated the adapted (ADP) strains by incubating CLIB 214 cells in the presence of increasing amounts of one of the three different antifungal drugs. Following direct selection, the evolved (EVO) strains were derived from the adapted strains by repeated culturing in yeast extract-peptonedextrose (YPD) without the previously used antifungal following a scheme that we previously described (10) and that is shown in Fig. 1.…”

“…Generation of azole-evolved strains. Triazole-evolved strains were generated as described previously (10,37), with minor modifications (Fig. 1).…”

“…All experiments were repeated two times. We defined the defect scores as described previously (10): a score of 1 was a strong defect, in which the growth of the given evolved strain spot, which was three times more concentrated than that of the most diluted CLIB 214 spot in which growth appeared, was reduced (smaller colonies or lower colony numbers); a score of 2 was a medium defect, in which similar numbers of CFU appeared in the given evolved strain spot, which was two times more concentrated than the most diluted CLIB 214 spot in which growth appeared; and a score of 3 was a slight defect, in which the growth in the given evolved strain spot at one time the concentration of the most diluted CLIB 214 spot in which growth appeared was reduced or colonies smaller than the parental strain's colonies were present. In vivo infection of mice and determination of fungal burden.…”

“…Despite the concern over high echinocandin MIC values in vitro, patients with C. parapsilosis infection generally respond well to echinocandin treatment (9). In a previous study, we revealed how this paradoxical phenomenon can be explained: acquired echinocandin resistance leads to attenuated virulence in vivo, possibly due to a fitness cost (10). Interestingly, while C. albicans clinical isolates are rarely resistant to azole derivatives, azole-resistant C. parapsilosis and C. glabrata strains are frequently isolated from patients (11).…”