Establishment of epidemiological cutoff values against Fonsecaea monophora, an agent of chromoblastomycosis and cerebral phaeohyphomycosis

Fonsecaea monophora is a dematiaceous fungus with worldwide distribution that can cause chromoblastomycosis, an implantation mycosis and a neglected tropical disease. F. monophora also causes phaeohyphomycosis, including central nervous system infections like brain abscesses, with high mortality rates. In the absence of clinical breakpoints, epidemiological cutoff values (ECVs) can aid clinicians in monitoring antifungal resistance trends and guide initial antifungal selection. To establish F. monophora MIC distribution and ECVs, we performed antifungal susceptibility testing (AFST) on F. monophora isolates. AFST data on F. monophora isolates were collected at 14 laboratories during September 2023-May 2026. Species identification was previously confirmed by DNA sequence analysis. AFST was performed by CLSI M38 standard broth microdilution method for itraconazole, voriconazole, posaconazole, isavuconazole, ketoconazole, terbinafine, flucytosine, and amphotericin B. The ECVs were established using the iterative statistical method with ECOFFinder (v2.1) following CLSI M57 guidelines. We analyzed MIC results from 137 F. monophora isolates. The calculated ECVs were itraconazole, 2 μg/mL; voriconazole, 0.25 μg/mL; posaconazole, 1 μg/mL; isavuconazole, 0.25 μg/mL; and terbinafine, 0.5 μg/mL. Amphotericin B and flucytosine had bimodal distributions, and no ECVs were set. Ketoconazole did not have data from ≥100 isolates. These F. monophora ECVs can detect non-wild-type isolates to reevaluate antifungal treatment and investigate treatment failure associated with potential clinical resistance. Established through a global multicenter collaboration, these values provide a baseline to better understand the in vitro antifungal susceptibility profile of this species and monitor resistance.IMPORTANCEFonsecaea monophora is a dematiaceous fungus with worldwide distribution that can cause chromoblastomycosis, an implantation mycosis and neglected tropical disease of the skin and subcutaneous tissue. F. monophora also causes phaeohyphomycosis, including central nervous system infections like brain abscesses with high mortality rates. The paucity of antifungal susceptibility testing data on F. monophora complicates interpretation of minimum inhibitory concentration (MIC) values. We performed antifungal susceptibility testing on 137 F. monophora isolates to establish MIC distributions and epidemiological cutoff values (ECVs) for eight antifungals, including those commonly used to treat F. monophora infections. The calculated ECVs for commonly used antifungals were 2 μg/mL for itraconazole, 0.25 μg/mL for voriconazole, 1 μg/mL for posaconazole, and 0.5 μg/mL for terbinafine. ECVs can assist in selecting potential treatments for F. monophora and tracking antifungal resistance trends.