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Ascomycota

Ascomycota are commonly know as sac fungi, cup fungi, earth tongues, cramp balls, dung buttons, truffles or moulds.

Most common moulds belonging to the Hyphomycetes are ascomycetes. They may be saprobes, parasites (especially of plants), or lichen forming, mostly terrestrial; cosmopolitan (50 orders, 275 families, 3328 genera, 32,325 spp). Ascomycetes are characterized by septate hyphae with simple pores. Asexual reproduction by conidia. Sexual reproduction by ascospores, typically eight, in an ascus.  Asci are often housed in a fruiting body or ascocarp e.g. cleistothecia or perithecia.

Species Descriptions

  • Aphanoascus fulvescens

    Aphanoascus fulvescens is a soil-borne keratinolytic ascomycete that occasionally causes dermatomycosis in humans and animals.

    RG-2 organism.

    Morphological Description:
    Colonies are moderately fast growing, white to tan with the production of numerous spherical, pseudoparenchymatous, buff to light brown cleistothecia (non-ostiolate ascocarps). Asci are subspherical to ellipsoidal and eight-spored. Ascospores light brown, yellowish to pale brown in mass, irregularly reticulate, lens-shaped, 3.5-4.7 x 2.5-3.5 µm. Aphanoascus fulvescens has a Chrysosporium anamorph showing typical pyriform to clavate-shaped conidia with truncated bases, 15-17.5 x 3.7-6 µm, which are formed either intercalary, laterally or terminally.

    Molecular Identification: 
    ITS sequencing will differentiate most species. The calmodulin gene may also be useful (Cano et al. 2002, Halliday et al. 2015).

    Key Features: 
    Keratinolytic, cleistothecia, and a Chrysosporium anamorph.

    References: 
    Domsch et al. (2007), McGinnis (1980), de Hoog et al. (2000, 2015), Cano and Guarro (1990), Cano et al. (2002).

  • Chaetomium

    The genus Chaetomium contains between 160 and 180 species. All are saprophytic being isolated from soil, straw, dung and plant debris. Several species are thermophilic and can grow at temperatures above 37C. Chaetomium species are important agents for the decomposition of cellulose waste and plant materials, and are only rarely isolated in medical mycology laboratories.

    RG-1 organisms.

    Morphological Description: 
    Chaetomium is a common ascomycete characterised by the formation of darkly-pigmented, globose, ovoid, barrel to flask-shaped, ostiolate ascocarps (perithecia) beset with dark-coloured terminal hairs (setae) which are straight, branched or curved. Asci are clavate to cylindrical, typically eight-spored and evanescent. Ascospores are one-celled, darkly-pigmented, smooth-walled, of varying shape, mostly ovoid, ellipsoidal or lemon-shaped. Chlamydospores and solitary conidia may also be produced.

    Molecular Identification: 
    Lee and Hanlin (1999) established the phylogenetic relationships of Chaetomium based on ribosomal DNA sequences. ITS sequencing may be useful for identification of some clinical species.

    Key Features: 
    Ascomycete producing darkly-pigmented ostiolate perithecia beset with long dark terminal setae.

    References: 
    Ames (1963), Seth (1970), Millner (1975), Domsch et al. (2007), Ellis and Keane (1981), Ellis (1981), von Arx (1986), de Hoog et al. (2000, 2015).

    Antifungal Susceptibility: Chaetomium species very limited data (McGinnis and Pasarell 1998a, Serena et al. 2003, Barron et al. 2003 and Australian National data); MIC µg/mL.
    Antifungal Range MIC90 Antifungal  Range MIC90
    AmB 0.125-16 4 VORI 0.125-0.5 0.5
    ITRA 0.03-0.25 0.125 POSA <0.03-1 0.5

A list of Mycology References cited for the identification of medically important fungi is available for viewing

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