Hepatic phaeohyphomycosis due to <i>Pleurostoma hongkongensis</i>, a novel species

Abstract

Background: The genus Pleurostoma houses Phialophora-like fungi which possess a creamy white-to-pale yellow colony appearance with no diffusible pigment and produce small-to-large, subspherical-to-allantoid conidia at the phialide tips. These fungi are mainly found in soil, woody plants, and sewage. Within this genus, P. repens, P. richardsiae, and P. ootheca have been reported to cause phaeohyphomycosis in humans. In this study, we isolated a novel dematiaceous mould pathogen, HKU44T, from a 65-year-old Chinese male patient. Preliminary morphological analysis and ITS sequencing showed that this fungus belonged to the genus Pleurostoma but its exact species identity could not be ascertained. Materials/methods: The clinical history of the patient was reviewed. The colony and microscopic morphologies of strain HKU44T was examined for its phenotyptic characteristics. The ITS, 18S rDNA, 28S rDNA, and β-tubulin gene of HKU44T , along with an additional 28 strains of the species P. richardsiae, P. ochraceum, P. repens, and P. ootheca were amplified by conventional PCR and sequenced. The DNA sequences were then compared with each other by pairwise alignment and the phylogenetic relationship of HKU44T and other Pleurostoma species were inferred using the maximum likelihood method. Results: Histological examination of the abscess wall biopsy collected from the patient showed numerous fungal hyphae. HKU44T, the mold recovered from the abscess sample, exhibited typical phenotypes shared by Pleurostoma species, including hyaline-to-pale brown colonies as well as branched, septate hyphae and subspherical, hyaline-to-brown conidia. Pairwise alignment of the ITS sequence of HKU44T and those of the type strains of P. richardsiae, P. ochraceum, P. repens, and P. ootheca showed 87.32%, 86.49%, 88.57%, and 88.87% similarities, respectively. Phylogenetic trees of all the four DNA markers showed that HKU44T is phylogenetically distinct from all four Pleurostoma species, although it is most closely related to P. ootheca and P. repens. The results suggested that HKU44T is a novel species of the genus Pleurostoma, which we propose to name it Pleurostoma hongkongenesis sp. nov. Conclusions: A novel fungal pathogen, Pleurostoma hongkongenesis., was discovered from the subhepatic abscess of a liver failure patient in Hong Kong, and this fungus is capable of causing invasive phaeohyphomycosis.