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

ABSTRACT

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.

KEYWORDS:

• Liver
• phaeohyphomycosis
• dematiaceous fungus
• Pleurostoma
• Pleurostoma hongkongense
• novel species

Acknowledgements

This work was partly supported by the Innovation and Technology Fund Midstream Research Programme for Universities (MRP/026/18) of the Innovation and Technology Commission, the Government of the Hong Kong Special Administrative Region. Any opinions, findings, conclusions or recommendations expressed in this material/event (or by members of the project team) do not reflect the views of the Government of the Hong Kong Special Administrative Region, the Innovation and Technology Commission or the Innovation and Technology Fund Research Projects Assessment Panel. We are grateful to Mrs Adrien Szekely of NCPF for providing the NCPF reference strains for free; Professor Maiken C. Arendrup and Dr Karin M. Jørgensen of SSI for providing the CNM-CL and CNM-CM reference strains for free; as well as the curators, especially Mr Travis W. Adkins, of NRRL for providing the NRRL reference strains for free. We also thank the Electron Microscope Unit of The University of Hong Kong which helped process the samples for scanning electron microscopy.

Disclosure statement

Patrick C. Y. Woo has provided scientific advisory/laboratory services for Gilead Sciences, Incorporated; International Health Management Associates, Incorporated; Merck & Corporation, Incorporated; Micología Molecular S.L. and Pfizer, Incorporated. The other authors report no conflicts of interest. The funding sources had no role in study design, data collection, analysis, interpretation, or writing of the report. The authors alone are responsible for the content and the writing of the manuscript. Part of this study has been presented as an abstract for the 30^th European Congress of Clinical Microbiology and Infectious Diseases.

Additional information

Funding

This work was partly supported by the Innovation and Technology Fund Midstream Research Programme for Universities (grant number MRP/026/18) of the Innovation and Technology Commission, the Government of the Hong Kong Special Administrative Region. Any opinions, findings, conclusions or recommendations expressed in this material/event (or by members of the project team) do not reflect the views of the Government of the Hong Kong Special Administrative Region, the Innovation and Technology Commission or the Innovation and Technology Fund Research Projects Assessment Panel.