Evolution of Fluconazole Resistance Mechanisms and Clonal Types of Isolates from a Tertiary Care Hospital in South Korea.

We investigated the evolution of fluconazole resistance mechanisms and clonal types of Candida parapsilosis isolates from a tertiary care hospital in South Korea. A total of 45 clinical isolates, including 42 collected between 2017 and 2021 and 3 collected between 2012 and 2013, were subjected to antifungal susceptibility testing, sequencing of fluconazole resistance genes (, , , and ), and microsatellite typing. Twenty-two isolates carried Y132F (=21; fluconazole MIC = 2 to >256 mg/L) or Y132F+R398I (=1; fluconazole MIC = 64 mg/L) in and four isolates harbored N1132D in (fluconazole MIC = 16 to 64 mg/L). All 21 Y132F isolates exhibited similar microsatellite profiles and formed a distinct group in the dendrogram. All four N1132D isolates displayed identical microsatellite profiles. Fluconazole MIC values of the Y132F isolates varied depending on their mutation status (number of isolates, year of isolation, and MIC): K177N (=8, 2012 to 2020, 2 to 8 mg/L); K177N + heterozygous G982R (=1, 2017, 64 mg/L); K177N + heterozygous S614P (2, 2019 to 2020, 16 mg/L); and K177N + homozygous S614P ( = 10, 2020 to 2021, 64 to > 256 mg/L). Our study revealed that Y132F in and N1132D in were the major mechanisms of fluconazole resistance in C. parapsilosis isolates. Furthermore, our results suggested that the clonal evolution of Y132F isolates persisting and spreading in hospital settings for several years occurred with the acquisition of heterozygous or homozygous mutations associated with a gradual increase in fluconazole resistance.