Spectrum of clinically significant melanized fungi in NIH hospitalized patients and their antifungal susceptibility profiles

Melanized fungi have occasionally been identified as causative agents of severe phaeohyphomycoses, chromoblastomycosis, and mycetoma. In a retrospective study conducted from January 2012 to December 2022, a total of 133 melanized fungi were isolated from hospitalized patients at the NIH Clinical Center, both with and without known underlying predisposing factors. Isolate identification was based on phenotypic characteristics, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS), and PCR sequencing of the rDNA internal transcribed spacer (ITS) region. Members of the black yeast order Chaetothyriales were the most prevalent (40, 30%), predominantly Exophiala dermatitidis (30/40, 75%). Other major groups included: Capnodiales (30, 22.6%), Pleosporales (24, 18%), Mycosphaerellales (19, 14.3%), Calosphaeriales (8, 6%), and Venturiales (7, 5.3%). MALDI-ToF often failed to accurately identify the isolates, except for E. dermatitidis, which yielded scores ≥2. ITS sequencing was effective in accurately identifying the melanized fungi encountered in clinical settings. Antifungal susceptibility testing against eight antifungal agents showed that azoles, micafungin, and terbinafine exhibited in vitro activity against most isolates. In contrast, olorofim and amphotericin B were less effective. Notably, Phaeoacremonium species (Calosphaeriales) exhibited distinct antifungal susceptibility patterns. Accurate identification of melanized fungi in clinical laboratories is essential for selecting effective antifungal therapy, understanding susceptibility patterns to available agents, supporting epidemiological monitoring, and ultimately enhancing clinical outcomes in patients affected by these often complex and opportunistic infections.