Hepatic phaeohyphomycosis due to a novel dematiaceous fungus, Pleurostoma hongkongense sp. nov., and importance of antifungal susceptibility testing

Pleurostoma species are wood-inhabiting fungi and emerging opportunistic pathogens causing phaeohyphomycosis. In this study, we isolated a dematiaceous fungus, HKU44 T , from the subhepatic abscess pus and drain fluids of a liver transplant recipient with post-transplant biliary and hepatico-jejunostomy bypass strictures. Histology of the abscess wall biopsy showed abundant fungal hyphae. The patient survived after a second liver transplant and antifungal therapy. On SDA, HKU44 T grew initially as white powdery colonies which turned beige upon maturation. Hyphae were septate and hyaline. Phialides were monophialidic and laterally located, generally closely associated to a cluster of conidia which were usually reniform. Phylogenetic analyses showed that HKU44 T is most closely related to, but distinct from, Pleurostoma ootheca and Pleurostoma repens. These suggested that HKU44 T is a novel Pleurostoma species, for which the name Pleurostoma hongkongense sp. nov. is proposed. Antifungal susceptibility testing showed that Pleurostoma species possessed high MICs/MECs for fluconazole, 5-flucytosine and the echinocandins; whereas they exhibited a high strain-to-strain variability to the susceptibilities to the other triazoles. As for amphotericin B, ∼65% of the Pleurostoma strains had low MICs (≤1 µg/mL). DNA sequencing should be performed to accurately identify fungi with Pleurostoma/Phialophora-like morphologies, so is antifungal susceptibility testing for patients with Pleurostoma infections.