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Exophiala

Exophiala species are common environmental fungi often associated with decaying wood and soil enriched with organic wastes. However, several species notably E. jeanselmei complex and E. spinier complex, are well documented human pathogens. Clinical manifestations include mycetoma (especially for E. jeanselmei complex), localized cutaneous infections, subcutaneous cysts, endocarditis and cerebral and disseminated infections. Phaeohyphomycosis caused by Exophiala species has been reported in both normal and immunosuppressed patients.

Species Descriptions

  • Exophiala dermatitidis

    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).

    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).

    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).

    Antifungal Susceptibility: E. dermatitidis (Duate et al. 2013 and Australian National data); MIC µg/mL.
    No <0.008 0.016 0.03 0.06 0.125 0.25 0.5 1 2 4 >8
    AmB 44 1 2 25 16
    VORI 44 4 12 20 1 4 2 1
    POSA 1 1
    ITRA 44 10 13 6 9 4 1 1
    E. dermatitidis data from 27 isolates (Fothergill et al. 2009); MIC µg/mL.
    AmB Range 0.125-1; MIC90 = 1 VORI Range 0.06-1; MIC90 = 0.25
    ITRA Range <0.015-0.5; MIC90 = 0.5 POSA Range <0.015-0.25; MIC90 = 0.06
  • Exophiala jeanselmei complex

    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.

    E. jeanselmei Mature conidiogenous cells rocket-shaped, slightly darker than the
    supporting hyphae, with regular tapering annellated zones.
    E. oligosperma Mature conidiogenous cells remain concolorous with supporting hyphae
    and may be intercalary and lateral, the latter being flask or rocket-shaped.
    Annellated zones have the appearance of inconspicuous flat scars.
    Chlamydospores are absent. 
    E. nishimurae  Similar morphology to E. oligosperma, however large
    chlamydospore-like cells are present.
    E. xenobiotica A segregant genotype of the E. jeanselmei complex with less
    melanised conidiogenous cells.
    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).

    Antifungal Susceptibility: E. jeanselmei (Australian National data); MIC µg/mL.
    No <0.008 0.016 0.03 0.06 0.125 0.25 0.5 1 2 4 >8
    AmB 9 1 3 2 2 1
    VORI 9 2 2 1 1 1 2
    POSA 6 1 2 2 1
    ITRA 9 2 3 2 2
    E. jeanselmei data from eight isolates (Fothergill et al. 2009); MIC µg/mL.
    AmB Range 0.125-1; MIC90 = 1 VORI Range 0.06-0.5; MIC90 = 0.5
    ITRA Range <0.015-0.125; MIC90= 0.125 POSA Range <0.015-0.03; MIC90= 0.03
    Exophiala oligosperma
    Antifungal Susceptibility: E. oligosperma  Australian National data); MIC µg/mL.
    No <0.008 0.016 0.03 0.06 0.125 0.25 0.5 1 2 4 >8
    AmB 2 2
    VORI 2 1 1
    POSA 2 1 1
    ITRA 2 1 1
    E. oligosperma data from 40 isolates (Fothergill et al. 2009); MIC µg/mL.
    AmB Range 0.125-1; MIC90 = 0.5 VORI Range <0.015-4; MIC90 = 2
    ITRA Range <0.015-0.25; MIC90 = 0.25 POSA Range <0.015-0.06; MIC90 = 0.03
    Exophiala xenobiotica
    Antifungal Susceptibility: E. xenobiotica (Australian National data); MIC µg/mL.
    No <0.008 0.016 0.03 0.06 0.125 0.25 0.5 1 2 4 >8
    AmB 3 1 1 1
    VORI 3 3
    POSA 3 1 2
    ITRA 2 2 1
    E. xenobiotica data from 39 isolates (Fothergill et al. 2009); MIC µg/mL.
    AmB Range 0.125-1; MIC90 = 0.5 VORI Range <0.015-2; MIC90 = 1
    ITRA Range <0.015-1; MIC90 = 0.125 POSA Range <0.015-0.06; MIC90 = 0.03
  • Exophiala spinifera complex

    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.

    E. spinifera  Annellated zones are long with clearly visible, frilled annellations.
    E. attenuata  Annellated zones are inconspicuous and degenerate.

    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).

    Antifungal Susceptibility: E. spinifera (Australian National data); MIC µg/mL.
    No <0.008 0.016 0.03 0.06 0.125 0.25 0.5 1 2 4 >8
    AmB 5 1 2 1 1
    VORI 5 1 2 2
    POSA 4 1 3
    ITRA 5 1 4
    E. spinifera data from eight isolates (Fothergill et al. 2009); MIC µg/mL.
    AmB Range 0.25-1; MIC90 = 1 VORI Range <0.06-0.5; MIC90 = 0.25
    ITRA Range <0.015-0.5; MIC90 = 0.125 POSA Range <0.015-0.03; MIC90 = 0.03

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