Studies on the phylogenesis of pathogenic 'black yeasts'

A Case of Recalcitrant Phaeohyphomycosis of the Face Caused by Exophiala lecanii-corni

We describe a case of recalcitrant phaeohyphomycosis caused by Exophiala lecanii-corni, which was previously reported as Exophiala jeanselmei, infection. A 63-year-old Japanese woman presented with a 15-year history of multiple pruritic erythematous patches and plaques on the face. Histopathological examination and fungal culture revealed phaeohyphomycosis by E. jeanselmei. The attempted treatments included 6 g/day 5-flucytosine (5-FC), 100 mg/day itraconazole (ITCZ), and local hyperthermia. 5-FC was effective initially, but the patient deteriorated after discontinuation. Subsequently, she was referred to our hospital. Histopathological examination showed granuloma with multinucleated giant cells with infiltrating fungal hyphae in the dermis. The causative fungus was finally identified as E. lecanii-corni by ribosomal RNA gene analysis. The patient improved after receiving 200 mg/day ITCZ orally for 15 months with local hyperthermia. In the present case, we confirmed the identification of E. lecanii-corni as the causative agent by molecular methods. We also emphasize the importance of combination therapy with antimycotic agents and local hyperthermia in phaeohyphomycosis.

Exophiala dermatitidis isolates from various sources: using alternative invertebrate host organisms (Caenorhabditis elegans and Galleria mellonella) to determine virulence

Exophiala dermatitidis causes chromoblastomycosis, phaeohyphomycosis and fatal infections of the central nervous system of patients with Asian background. It is also found in respiratory secretions from cystic fibrosis (CF) patients. In this study a variety of E. dermatitidis strains (isolates from Asia, environmental and CF) were characterized in their pathogenicity by survival analyzes using two different invertebrate host organisms, Caenorhabditis elegans and Galleria mellonella. Furthermore, the morphological development of hyphal formation was analyzed. E. dermatitidis exhibited pathogenicity in C. elegans. The virulence varied in a strain-dependent manner, but the nematodes were a limited model to study hyphal formation. Analysis of a melanin-deficient mutant (Mel-3) indicates that melanin plays a role during virulence processes in C. elegans. The strains isolated from Asian patients exhibited significantly higher virulence in G. mellonella compared to strains from other sources. Histological analyzes also revealed a higher potential of invasive hyphal growth in strains isolated from Asian patients. Interestingly, no significant difference was found in virulence between the Mel-3 mutant and their wild type counterpart during infection in G. mellonella. In conclusion, invasive hyphal formation of E. dermatitidis was associated with increased virulence. This work is the basis for future studies concerning E. dermatitidis virulence.

The mycobiota of the salterns

Solar salterns are constructed as shallow multi-pond systems for the production of halite through evaporation of seawater. The main feature of salterns is the discontinuous salinity gradient that provides a range of well-defined habitats with increasing salinities, from moderate to hypersaline. These present one of the most extreme environments, because of the low levels of biologically available water and the toxic concentrations of ions. Up to the year 2000, hypersaline environments were considered to be populated almost exclusively by prokaryotic microorganisms till fungi were reported to be active inhabitants of solar salterns. Since then, numerous fungal species have been described in hypersaline waters around the world. The mycobiota of salterns is represented by different species of the genus Cladosporium and the related meristematic melanized black yeasts, of non-melanized yeasts, of the filamentous genera Penicillium and Aspergillus and their teleomorphic forms (Eurotium and Emericella), and of the basidiomycetous genus Wallemia. Among these, two species became new model organisms for studying the mechanisms of extreme salt tolerance: the extremely halotolerant ascomycetous black yeast Hortaea werneckii and the obligate halophilic basidiomycete Wallemia ichthyophaga.

Identification, classification, and phylogeny of the pathogenic species Exophiala jeanselmei and related species by mitochondrial cytochrome b gene analysis

We analyzed a 402-bp sequence of the mitochondrial cytochrome b gene of 34 strains of Exophiala jeanselmei and 16 strains representing 12 related species. The strains of E. jeanselmei were classified into 20 DNA types and 17 amino acid types. The differences between these strains were found in 1 to 60 nucleotides and 1 to 17 amino acids. On the basis of the identities and similarities of nucleotide and amino acid sequences, some strains were reidentified: i.e., two strains of E. jeanselmei var. hetermorpha and one strain of E. castellanii as E. dermatitidis (including the type strain), three strains of E. jeanselmei as E. jeanselmei var. lecanii-corni (including the type strain), three strains of E. jeanselmei as E. bergeri (including the type strain), seven strains of E. jeanselmei as E. pisciphila (including the type strain), seven strains of E. jeanselmei as E. jeanselmei var. jeanselmei (including the type strain), one strain of E. jeanselmei as Fonsecaea pedrosoi (including the type strain), and one strain of E. jeanselmei as E. spinifera (including the type strain). Some E. jeanselmei strains showed distinct nucleotide and amino acid sequences. The amino-acid-based UPGMA (unweighted pair group method with the arithmetic mean) tree exhibited nearly the same topology as those of the DNA-based trees obtained by neighbor joining, maximum parsimony, and maximum likelihood methods.

Report of chronic subcutaneous abscesses caused by Exophiala spinifera

A case of phaeohyphomycosis with subcutaneous abscesses involving skin, muscle and bone was caused by Exophiala spinifera. This is the first report of E. spinifera causing bone degeneration in Recife-PE, Brazil.

Clinical and mycological spectra of Wangiella dermatitidis infections

The article reviews 37 cases of phaeohyphomycosis from the world literature up to 1992 accepted as being caused by Wangiella dermatitidis. The various clinical aspects of these infections are characterized, and the nomenclatural implications in the history of this emerging pathogen are discussed.

Mitochondrial DNA analysis of Exophiala jeanselmei and Exophiala dermatitidis

Mitochondrial DNA (mtDNA) analysis with Hae III, Hind III and Msp I was performed in 45 Exophiala jeanselmei strains (30 Phialophora jeanselmei and 154 Phialophora gougerotii strains) and 31 Exophiala dermatitidis strains. The results were as follows, 1) P. jeanselmei and P. gougerotii are identical, 2) E. jeanselmei is classified into 18 types based on restriction profiles, 3) two strains of E. jeanselmei CBS 577.76 and CBS 578.76 are identified as E. dermatitidis, 4) E. dermatitidis has no intraspecific variation and is definitely distinct from E. jeanselmei, 5) E. jeanselmei is suggested to be a complex organism because of extensive mtDNA polymorphism.

Exophiala pisciphila. A study of its development

Exophiala pisciphila is a dematiaceous fungus that belongs to a group of fungi known as the 'black yeasts'. It was isolated from the skin lesions of a smooth dogfish, Mustelus canis Mitchill, that had been born in the shark exhibit tank of the New York Aquarium. The different stages of development of this fungus were studied by light microscopy and scanning electron microscopy to illustrate the morphology and surface structures of conidia and mycelium. The list of marine and fresh water fish, which have been infected by Exophiala spp. and Exophiala-like fungi has been up-dated. Potato Dextrose Agar and Malt Agar proved to be the best growth media, while Corn Meal Agar proved to be the best medium for studying the morphological features of the conidia and mycelial development of E. pisciphila, which exhibited polymorphic conidiogenesis.

Further studies on the phylogenesis of the genus Exophiala and Hortaea

The conidial ontogenesis of the pathogenic black yeasts is studied at an ultrastructural level and their phylogenesis is discussed. Five cultures of Exophiala dermatitidis, four of E. jeanselmei, one of E. moniliae, one of E. spinifera and six of H. werneckii were observed using a scanning electron microscope. The conidial ontogenesis of the Exophiala species is not pleomorphic but only annellidic. There are definite differences in morphology of annellated tips among the Exophiala species. The ontogenesis of Hortaea werneckii consists of a combination of sympodial and annellidic conidiogenesis. Its sympodial anamorph is unique and the annellidic anamorph is considered to be a homology of the sympodial one.

Pathogenicity of Exophiala jeanselmei for ddY mice

The pathogenicity of three cultures isolated as Phialophora jeanselmei was compared with that of three cultures of Phialophora gougerotii using ddY mice. One hundred and twenty mice were used. They were divided into 6 groups consisting of 20 each. Each culture was evaluated in 20 mice. Mice were inoculated intravenously with 0.2 ml of a 1% (wet weight/vol.) yeast-like cell suspension and sacrificed at adequate intervals until the 30th day. As results, 1) the virulence of the three cultures each of P. jeanselmei and P. gougerotii to ddY mice was mild. 2) These cultures were not neurotropic. 3) P. gougerotii survived longer in the mice than P. jeanselmei. 4) There were no major differences in histopathology of the lesions in the mice inoculated with the two taxa.