Phialophora dermatitidis; its morphology and biology

Exophiala oligosperma causing olecranon bursitis

A 62-year-old male with a history of Wegener's granulomatosis and immunosuppressive therapy presented with chronic olecranon bursitis. A black velvety mould with brown septate hyphae and tapered annellides was isolated from a left elbow bursa aspirate and was identified as an Exophiala species. Internal transcribed sequence rRNA sequencing showed the isolate to be identical to Exophiala oligosperma. The patient was successfully treated with aspiration and intrabursal amphotericin B.

Fruiting studies in species of Capronia (Herpotrichiellaceae)

A recently described protocol for the in vitro production of ascomata was employed to determine the sexual incompatibility systems of five species of Capronia. The formation of mature ascomata in isolates derived from single ascospores demonstrated that C. epimyces, C. mansonii, and C. munkii n. sp. are homothallic. In contrast, fertile ascomata were observed only in mass-ascospore isolates and pairwise crosses between specific single-ascospore isolates in C. dactylotricha n. sp. and C. moravica. The Exophiala anamorphs of C. dactylotricha and C. munkii are described and a Phialophora-like synanamorph is reported for the former species. Germinating ascospores of C. munkii formed conidiogenous cells directly, while the ascospores of the remaining species germinated to produce germ tubes and hyphae. The application of the terms 'microcyclic conidiation' to secondary conidium production and 'sclerotial body' and 'stroma' to the multicellular structures produced by species of Capronia and Exophiala are discussed.

Pleoanamorphic life cycle of Exophiala (Wangiella) dermatitidis

The anamorph life cycle of the black yeast Exophiala (Wangiella) dermatitidis is described. The fungus is dimorphic, yeast cells being the prevalent form of propagation. The fungus is strongly hydrophilic, probably completing its anamorph life cycle in submersion. Adaptation to dry conditions is slow. Types of conidiogenesis comprise annellidic, phialidic and sympodial reproduction, in addition to isotropic development. Phialoconidia fail to germinate under the conditions tested, and thus may have a function other than dispersal. Sterile, multicellular bodies resembling a Capronia teleomorph are described.

Phaeohyphomycosis caused by Exophiala jeanselmei treated with itraconazole

Phaeohyphomycotic cysts developed on the right knee of a 72-year-old woman undergoing immunosuppressive treatment for ulcerative colitis 6 years after accidental inoculation of soil in a bicycle accident. The lesions were red, firm, slightly raised, 0.5-1 cm in size and completely asymptomatic. The diagnosis was made by histopathological examination of three excised cysts and by repeated isolation of Exophiala jeanselmei in pure culture. The excised cyst walls contained large numbers of dematiaceous fungal elements in the form of hyphae, yeast-like cells and some cells dividing internally by a transverse septum. The patient was treated with 200 mg of itraconazole daily, but the treatment had to be stopped because of severe side-effects after 6 weeks. Histologically the cysts were cleared of dematiaceous elements, but E. jeanselmei could still be isolated from one of two skin biopsies 1 month after the end of therapy.

Nutritional physiology and selective isolation of Exophiala dermatitidis

The nutritional physiology of ten strains of Exophiala dermatitidis was investigated. The growth reactions to lactose, citrate, nitrate, nitrite, lysine, creatine and creatinine differ from those found in closely related black yeasts. In addition, it is the only Exophiala species which is able to grow at 40 degrees C. A selective medium containing meso-erythritol as sole carbon source was evaluated. This medium is particularly useful for the isolation of black yeasts from lungs of patients with cystic fibrosis as well as from the environment.

Cerebral phaeohyphomycosis caused by an Exophiala species

A 45-year-old woman was found to have cerebral phaeohyphomycosis caused by an Exophiala species. The portal of entry of the fungus remained unknown. Despite surgery and antimycotic therapy the patient died from circulation failure. The fungus is compared to several related Exophiala species.

Deoxyribonucleic acid hybridization studies of Exophiala dermatitidis and Exophiala jeanselmei

Exophiala dermatitidis and Exophiala jeanselmei share similar morphological features and have been confused with each other. To clarify the relationship between the two fungi, we conducted a deoxyribonucleic acid (DNA)-DNA hybridization study using a dot blot method. Between E. dermatitidis and E. jeanselmei, only a very low level of DNA relatedness was seen and it was confirmed that these two fungi are distinct species based on DNA similarity. Close correspondence of DNA from the isolates of E. dermatitidis was obtained, whereas the isolates of E. jeanselmei were divided into 6 groups according to their DNA similarity and a possibility was shown that E. jeanselmei is composed of genetically heterogeneous groups. The subdivision of the species E. jeanselmei by the DNA-DNA hybridization method was in agreement with serotyping exoantigens. This result suggests that DNA-DNA hybridization studies provide an excellent tool for the identification and grouping of pathogenic dematiaceous fungi.

Sarcinomyces phaeomuriformis: a new dematiaceous hyphomycete

Sarcinomyces phaeomuriformis is described as a new species in the genus Sarcinomyces Lindner. Currently, the taxon is known to occur only in Japan as a causal agent of phaeohyphomycosis. The colonies are initially yeast-like, which on aging become dry, granular, heaped, friable and black. The initial growth consists of single cells which form multiple broad-based buds and by a successive budding process produce chains of blastoconidia. In its blastic conidiogenesis, S. phaeomuriformis resembles Phaeococcomyces catenatus. However, mature colonies consist of thick-walled, pale to dark brown muriform cells which develop broad-based buds. The buds, after separating from their parent cells, either bud or enlarge and divide internally by septations laid down in different planes to become muriform. Conidiogenesis that gives rise to multiple, broad-based blastic and thallic-sarcinic conidia characterizes S. phaeomuriformis.

Use of carbohydrate and nitrate assimilations in the identification of dematiaceous fungi

A total of 61 isolates of dematiaceous fungi, including Exophiala jeanselmei, Wangiella dermatitidis, Fonsecaea pedrosoi, Phialophora verrucosa, and a few isolates of related organisms were evaluated for their ability to assimilate 13 carbohydrates and sodium nitrate. Results indicated that patterns of assimilations can facilitate specific identifications when used with microscopic morphologic features. Eleven isolates of W. dermatitidis demonstrated negative results for nitrate assimilation, although most of the other fungi tested had positive reactions. The tests did aid in separating this very complex group of fungi.

Pathogenicity of a fungus resembling Wangiella dermatitidis isolated from edible mushrooms

A fungus resembling the human pathogen Wangiella dermatitidis (Kano) McGinnis, a dematiaceous hyphomycete, was recovered from imported desiccated "black fungus" mushrooms (Auricularia polytrichia (Mont.) Sacc.), a food item popular in Far Eastern cuisine. Except for its conidia, which are mostly reniform to allantoid rather than ovoid as is characteristic for W. dermatitidis, and the undecided mode of conidiogenesis, the isolate closely resembles W. dermatitidis in gross and microscopic morphology, thermotolerance, and general and neurotrophic infectivity patterns in mice injected intraperitoneally. The foodborne isolate was also infective for infant mice inoculated by oral intubation. The systematic position of the isolate is still under investigation. There has been no previous report of W. dermatitidis or of a fungus resembling it occurring in or on foods or of the infectivity of a fungus for a mammalian host by oral intubation.

Studies on the phylogenesis of pathogenic 'black yeasts'

This paper deals mainly with the conidium ontogenesis and phylogenesis of black yeasts such as E. jeanselmei, E. gougerotii, E. dermatitidis and E. spinifera. The conidium ontogenesis of E. jeanselmei, E. gougerotii and E. dermatitidis was almost the same. One to five annellated tips were observed through a scanning microscope at the apices of conidiogenous cells, which were bottle- or jar-shaped. Annellations on the tips looked like fringes and the conidiogenous cells of these three species were annellides. Annellated projections occurred on hyphae and annelloconidia were also produced from them. Occasionally, secondary annellides occurred from primary ones. They looked like moniliform hyphae. Daughter conidia sometimes budded directly from mother cells. The shapes and sizes of the conidia of these species were very similar to each other. The conidium ontogenesis of E. spinifera was annellidic as well. However, a single annellated tip usually occurred on an annellide. The annellated tips of the fungus were long and more than 20 annellations were observed on their walls. The conidiogenesis of the four species of Exophiala is only annellidic. There were no differences in the biological examinations except KNO3 assimilation among these four species. The growth of E. jeanselmei and E. gougerotii was poor at 37 degrees C. The GC contents of E. jeanselmei 1171, E. gougerotii B-1800, E. dermatitidis MM-7 and E. spinifera DU-3342 were 54.6, 54.6, 56.6 and 59.7%, respectively.

Serological analysis and pathogenic potentials of Wangiella dermatitidis isolated from bats

Five isolates of Wangiella dermatitidis from macroscopically asymptomatic bats were analysed by the agar-gel immunodiffusion tests and the mouse inoculation studies on virulence. No cross-reactivity among the antigens and antisera prepared from the bat and human isolates was observed. The fungus was shown to be neurotropic, of low infectivity and not implicated as a potential opportunistic pathogen. Differences in the antigenic composition and pathogenic potentials between isolates of the same fungus of different origins may reflect adaptation of the fungus in different hosts.

Nuclear division in temperature-sensitive multicellular mutants of Wangiella dermatitidis

Temperature-sensitive morphological mutants of Wangiella dermatitidis were stained with mithramycin, a fluorescent nuclear stain. Multicellular forms of the mutants each contained two or more nuclei, documenting that nuclear division accompanied the yeast-to-multicellular form conversion.

Thermotolerance of Wangiella dermatitidis

A variety of diagnostic tests used by many laboratories to identify isolates of Wangiella dermatitidis (= Fonsecaea dermatitidis) were evaluated. Thirteeen isolates of W. dermatitidis were studied with respect to their ability to grow at 25, 37, 40, 45, and 50 degrees C, colonial and micromorphology, gelatin liquefaction, and hydrolysis of casein, xanthine, hypoxanthine, and tyrosine. All 13 isolates showed growth at 25, 37, and 40 degrees C but failed to grow at higher temperatures. The ability of W. dermatitidis to grow at 40 degrees C can be useful in its identification.

Temperature-sensitive multicellular mutants of Wangiella dermatitidis

Three temperature-sensitive morphological mutants of Wangiella dermatitidis were isolated and characterized. The mutants grew in the yeastlike morphology at the permissive temperature (25 degrees C) but expressed a multicellular (Mc) phenotype at the restrictive temperature (37 degrees C). Cultures of Mc 2 and 3 incubated at the restrictive temperature showed rapid reductions in the percentage of budded cells in the population. In contrast, budding continued for several generations in cultures of Mc 1. Incubation of cultures of Mc 2 and 3 at the restrictive temperature for 48 h resulted in nearly total conversion of yeastlike cells to the multicellular form; about 50% of the cells of Mc 1 had converted to multicellular forms after 48 h at the restrictive temperature. Studies using radiolabeled compounds documented that DNA, RNA, and protein synthesis continued at the restrictive temperature. The results suggest that multicellularity is the result of inhibition of bud emergence and cell separation without inhibition of growth nuclear division, and cytokinesis.

Effect of carbon source on conidiogenesis in Fonsecaea dermatitidis, agent of chromomycosis

Hormiscium dermatitidis Kano is a well known etiological agent of cutaneous and generalized chromomycosis. However, the generic designation of this fungus has long been a much debated question. The results of the present study of the type culture ATCC 28869 indicate that the fungus is polymorphic, producing a Phialophora state in media containing glucose or maltose and a Cladosporium state in media containing galactose or melibiose. Morphologically and developmentally this chromomycotic agent is closely related to Fonsecaea pedrosoi (Brumpt) Negroni and should be classified as Fonsecaes dermatitidis (Kano) Carrion.

Budding in the dimorphic fungus Phialophora dermatitidis

Ultrastructural comparisons of yeast and hyphal bud formation in Phialophora dermatitidis reveal that bud initiation is characterized by a blastic rupture of the outer portion of the yeast or hyphal wall and the emergence of a bud protuberance through the resulting opening. The wall of the emerging bud is continuous, with only an inner wall layer of the parental yeast or hypha. The outer, ruptured portion of the parental wall typically forms a collar around the constricted emergence region of the developing bud. The cytoplasm within the very young emerging bud invariably contains a small number of membrane-bound vesicles. The septum formed between the daughter bud and the parental yeast or hypha is a complete septum devoid of a septal pore, septal pore plug, or any associated Woronin bodies characteristic of simple septa of the moniliform or true hyphae. These observations suggest that yeast bud formation and lateral hyphal bud formation in the dimorphic fungus P. dermatitidis involve a growth process which occurs identically in both the yeast and mold phase of this human pathogenic organism.

Morphologica and structural changes during the yeast-to mold conversion of Phialophora dermatitidis

The details of the morphological and structural events occurring during yeast-to-mold conversion of the human pathogenic fungus Phialophora dermatitidis as seen by phase-contrast microscopy and electron microscopy are described and illustrated. Budding yeasts growing exponentially were observed to have thin walls and a cytoplasm exhibiting the characteristics of rapidly growing cells including numerous mitochondria, abundant ribosomes, few vacuoles, and little accumulation of storage material. In contrast, thick-walled yeasts were characterized by less apparent or significantly fewer mitochondria and ribosomes and the presence of considerable amounts of storage materials. Microscope observations of yeast-to-mold conversion revealed that only thick-walled yeasts having prominent lipid bodies in their cytoplasm converted to hyphal forms. Typically, the thick-walled yeast formed two to a number of moniliform hyphal cells which in turn often produced true hyphae. The results indicated that yeasts of P. dermatitidis must acquire spore-like characteristics by becoming thick-walled and by accumulating considerable endogenous substrate reserves before they convert and produce hyphae.