Diversity of novel and emerging pathogenic fungi in Hong Kong

Abstract

The incidence of mycotic infections, especially in immunocompromised individuals, is on the rise. The application of molecular identification has recognised a number of fungi, particularly those previously considered nonpathogenic, as emerging causes of mycoses. Yet, the aetiology for quite a number of fungal infections remains unknown. In the present study, it was hypothesised that novel and emerging pathogenic fungi could be identified using the consolidated species recognition method. The aim of the current project was to characterise the clinical spectrum of these novel and emerging fungal pathogens in Hong Kong.

A total of 54 clinical, veterinary, and associated environmental fungi were retrieved and included in this work. These fungi, together with 45 related reference strains, were studied by phenotypic characterisation (including the examination of macro- and micromorphologies, growth test, and/or biochemical profiling), molecular phylogenetics (based on the internal transcribed spacer region, 18S and/or 26S/28S nuclear ribosomal DNAs, and/or other housekeeping protein-coding genes), matrix-assisted laser desorption/ionisation–time-of-flight mass spectrometry (MALDI–TOF MS), and/or antifungal susceptibility test. This polyphasic approach revealed that 38 of these 54 fungal strains represented 23 different described species across three different ascomycetous classes. Many of these species are uncommon aetiological agents of fungal infections, yet their clinical significance should not be underestimated. One of these species, Engyodontium album, was found to be phylogenetically and chemotaxonomically distantly related to its parent genus. Three of the remaining strains (HKU35T, HKU39T, and HKU49T) exhibited morphological features different from any other known fungal species and were found to occupy phylogenetic and/or chemotaxonomic positions distinct from other closely related species. New genera and/or species were proposed to describe these fungal taxonomic novelties.

The novel fungi Hongkongmyces pedis genus novum et species nova and Phialemoniopsis hongkongensis species nova were recognised as causes of subcutaneous phaeohyphomycoses. The opportunistic pathogen Engyodontium album was transferred to Parengyodontium genus novum, and the new name Parengyodontium album combinatio nova was erected. A third previously unknown species, Aspergillus hongkongensis species nova, was also described as the aetiological agent of onychomycosis. Moreover, several other Aspergillus species (including Aspergillus flavus, Aspergillus sydowii, Aspergillus terreus, Aspergillus tubingensis, Aspergillus unguis, and Aspergillus welwitschiae), 14 nondermatophytic moulds (including Acremonium sclerotigenum–Acremonium egyptiacum complex, Cephalotheca foveolata, Chaetomium globosum, Cladosporium halotolerans, Cladosporium lebrasiae, Didymella gardeniae, Exophiala oligosperma, Microascus gracilis, Nigrospora sphaerica, Pithomyces maydicus, Purpureocillium lilacinum, Rhinocladiella similis, Sagenomella keratitidis, and Simplicillium obclavatum), and six additional potentially novel fungal species (of the families Amorosiaceae, Sympoventuriaceae, or Trichomeriaceae; or of the genera Arthrinium, Paracremonium, or Pyrenochaetopsis) were found to be emerging agents of nail infections. The emergence of Trichomonascus ciferrii as causes of human granular myringitis and Fusarium solani species complex as causes of systemic infections in elasmobranchs was also recognised. There was a large variation in the antifungal susceptibility profiles amongst the clinical/veterinary fungal isolates tested, highlighting the importance of accurate species identification for the determination of suitable treatments for patient management.

In conclusion, a diverse spectrum of less well-known fungi has been recognised as emerging infectious agents. Three novel pathogenic fungi were also discovered and described.