Among emerging non-albicans Candida species, Candida parapsilosis is of particular concern as a cause of nosocomial
bloodstream infections in neonatal and intensive care unit patients. While
fluconazole and
echinocandins are considered effective treatments for such
infections, recent reports of
fluconazole and
echinocandin resistance in C. parapsilosis indicate a growing problem. The present study describes a novel mechanism of antifungal resistance in this organism affecting susceptibility to
azole and
echinocandin antifungals in a clinical isolate obtained from a patient with prosthetic valve
endocarditis. Transcriptome analysis indicated differential expression of several genes in the resistant isolate, including upregulation of
ergosterol biosynthesis pathway genes ERG2, ERG5, ERG6, ERG11, ERG24, ERG25, and UPC2 Whole-genome sequencing revealed that the resistant isolate possessed an ERG3 mutation resulting in a G111R amino acid substitution.
Sterol profiles indicated a reduction in
sterol desaturase activity as a result of this mutation. Replacement of both mutant alleles in the resistant isolate with the susceptible isolate's allele restored wild-type susceptibility to all
azoles and
echinocandins tested. Disruption of ERG3 in the susceptible and resistant isolates resulted in a loss of
sterol desaturase activity, high-level
azole resistance, and an
echinocandin-intermediate to -resistant phenotype. While disruption of ERG3 in C. albicans resulted in
azole resistance,
echinocandin MICs, while elevated, remained within the susceptible range. This work demonstrates that the G111R substitution in Erg3 is wholly responsible for the altered
azole and
echinocandin susceptibilities observed in this C. parapsilosis isolate and is the first report of an ERG3 mutation influencing susceptibility to the
echinocandins.