First Case of Candidemia Caused by Fluconazole-Resistant Candida orthopsilosis Harboring the ERG11 G458S Mutation in a Hematopoietic Stem Cell Transplant Recipient in Asia.

Candidemia poses a life-threatening complication for immunocompromised patients, including those undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). Non-albicans Candida species are increasingly recognized as causative pathogens in this population, with azole resistance having emerged as a global concern. Candida orthopsilosis, a member of the Candida parapsilosis species complex, is generally considered susceptible to azole antifungal agents. Although sporadic reports of azole-resistant isolates have surfaced worldwide, no such cases have been documented in Japan. Furthermore, genetic evaluations of azole-resistant C. orthopsilosis have primarily been conducted in Europe. We present the first case of fluconazole-resistant C. orthopsilosis bloodstream infection in a 73-year-old man following allo-HSCT for acute myeloid leukemia in Japan. Whole-genome sequencing identified an ERG11 G458S substitution, a known mechanism of fluconazole resistance in C. orthopsilosis, representing the first identification of this mutation outside Europe. Our findings highlight the importance of continued surveillance of antifungal resistance in C. orthopsilosis.