Exophiala

Synonymy: 
Wangiella dermatitidis, Phaeococcomyces exophialae.

Exophiala dermatitidis has been isolated from plant debris and soil and is a recognised causative agent of mycetoma and phaeohyphomycosis in humans (Zeng et al. 2007; Kirchhoff et al., 2019).

RG-2 organism.

Morphological description: 
Colonies are slow growing, initially yeast-like and black, becoming suede-like, olivaceous-grey with the development of aerial mycelium with age. A brown pigment is often produced in the agar. The initial yeast-like phase is characterised by unicellular, ovoid to elliptical, budding yeast-like cells. The yeast-like cells are hyaline and thin-walled when young becoming darkly pigmented (dematiaceous) and thick-walled when mature. With the development of mycelium, flask-shaped to cylindrical annellides are produced. Conidia are hyaline to pale brown, one-celled, round to obovoid, 2-4 x 2.5-6 µm, smooth-walled and accumulate in slimy balls at the apices of the annellides or down their sides. Cultures grow at 42C and on media containing 0.1% cycloheximide.

Molecular identification:
ITS and/or D1/D2 sequencing is recommended for species identification (Halliday et al. 2015).

MALDI-ToF MS:
Appears to be a promising identification tool with an extensive database (Kondori et al., 2015; Ozhak-Baysan et al., 2015).

 References: 
de Hoog and Hermanides-Nijhof (1977), McGinnis (1980), Hohl et al. (1983), Nishimura and Miyaji (1983), Matsumoto et al. (1984), Dixon and Polak-Wyss (1991), de Hoog et al. (2000, 2015).

Exophiala jeanselmei has a worldwide distribution and is a recognised causative agent of mycetoma and phaeohyphomycosis in humans. Zeng et al. (2007) presented an overview of the medically important Exophiala species.

E. jeanselmei has long been recognised as heterogeneous (de Hoog 1977). Recent molecular studies have redefined Exophiala jeanselmei and three additional species have been identified: E. oligosperma, E. nishimurae and E. xenobiotica (Vitale and de Hoog, 2002, de Hoog et al. 2003, 2006). These species are morphologically very similar and can best be distinguished by genetic analysis Zeng et al. (2014).

Molecular identification: 
ITS and/or D1/D2 sequencing is recommended for species identification (Halliday et al. 2015).

Morphological description:
Conidiogenous cells are predominantly annellidic and erect, multicellular conidiophores are absent. No growth at 40C.

Exophiala jeanselmei

RG-2 organism.

Morphological description: 
Colonies are initially smooth, greenish-grey to black, mucoid and yeast-like, becoming raised and developing tufts of aerial mycelium with age, often becoming dome-shaped and suede-like in texture. Reverse is olivaceous-black. Numerous ellipsoidal, yeast-like, budding cells are usually present, especially in young cultures. Scattered amongst these yeast-like cells are larger, inflated, subglobose to broadly ellipsoidal cells (germinating cells) which give rise to short torulose hyphae that gradually change into unswollen hyphae. Conidia are formed on lateral pegs either arising apically or laterally at right or acute angles from essentially undifferentiated hyphae or from strongly inflated detached conidia. Conidiogenous pegs are 1-3 µm long, slightly tapering and imperceptibly annellate. Conidia are hyaline, smooth, thin-walled, broadly ellipsoidal, 3.2-4.4 x 1.2-2.2 µm, and with inconspicuous basal scars. Cultures grow at 37C but not at 40C.

 References: 
de Hoog and Hermanides-Nijhof (1977), de Hoog (1977, 1985), McGinnis and Padhye (1977), McGinnis (1978b, 1980), Domsch et al. (1980), Nishimura and Miyaji (1983), Matsumoto et al. (1987), Dixon and Polak-Wyss (1991), Badali et al. 2010, de Hoog et al. (2000, 2003, 2006, 2015).

Exophiala oligosperma

Exophiala xenobiotica

Synonymy: 
Phialophora spinifera; Rhinocladiella spinifera

E. spinifera has a worldwide distribution and is a recognised causative agent of mycetoma and phaeohyphomycosis in humans. Zeng et al. (2007) presented an overview of the medically important Exophiala species.

Recent molecular studies have re-examined Exophiala spinifera and have recognised two species: E. spinifera and E. attenuata (Vitale and de Hoog, 2002). These two species are morphologically very similar and can best be distinguished by genetic analysis.

Molecular identification: 
ITS sequencing is recommended for accurate species identification (Zeng and de Hoog, 2008).

Morphological description: 
Conidiogenous cells are predominately annellidic and erect, multicellular conidiophores that are darker than the supporting hyphae are present. No growth at 40C.

Exophiala spinifera

RG-2 organism.

Morphological description: 
Colonies are initially mucoid and yeast-like, black, becoming raised and developing tufts of aerial mycelium with age, finally becoming suede-like to downy in texture. Reverse is olivaceous-black. Conidiophores are simple or branched, erect or sub-erect, spine-like with rather thick brown pigmented walls. Conidia are formed in basipetal succession on lateral pegs either arising apically or laterally at right or acute angles from the spine-like conidiophores or from undifferentiated hyphae. Conidiogenous pegs are 1-3 µm long, slightly tapering and imperceptibly annellate. Conidia are one-celled, subhyaline, smooth, thin-walled, sub-globose to ellipsoidal, 1.0-2.9 x 1.8-2.5 µm, and aggregate in clusters at the tip of each annellide. Toruloid hyphae and yeast-like cells with secondary conidia are typically present.

Note: 
Yeast cells show the presence of capsules in India Ink stained mounts and cultures will grow on media containing 0.1% cycloheximide. No growth at 40C.

 References: 
de Hoog and Hermanides-Nijhof (1977), McGinnis and Padhye (1977), Domsch et al. (1980), McGinnis (1980), Nishimura and Miyaji (1983), de Hoog (1985), Matsumoto et al. (1987), Dixon and Polak-Wyss (1991), de Hoog et al. (2000, 2003, 2006, 2015).