DESCRIPTIONS OF MEDICAL FUNGI

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Descriptions of Medical Fungi
Microsporum Gruby
A recent multilocus phylogenetic study the has reviewed the taxonomy of the
dermatophytes. Arthroderma now contains 21 species, Epidermophyton one species,
Lophophyton one species, Microsporum three species, Nannizzia nine species
and Trichophyton 16 species. In addition, two new genera have been introduced:
Guarromyces containing one species and Paraphyton three species (de Hoog et al.
2016).
The genus Microsporum is now restricted to just three species: M. audouinii, M.
canis and M. ferrugineum. The remaining geophilic and zoophilic species, previously
considered Microsporum species, have been transferred to the genera Lophophyton
and Nannizzia.
Microsporum species may form both macro- and microconidia, although they are not
always present. Cultures are mostly granular to cottony, yellowish to brownish, with a
cream-coloured or brown colony reverse. Macroconidia are hyaline, multiseptate, with
thick rough cell walls, and are clavate, fusiform or spindle-shaped. Microconidia are
single-celled, hyaline, smooth-walled, and are predominantly clavate in shape.
Note: Strains of M. canis often do not produce macroconidia and/or microconidia on
primary isolation media and subcultures onto polished rice grains or lactritmel agar
are recommended to stimulate sporulation. These non-sporulating strains of M. canis
are often erroneously identified as M. audouinii and it is surprising just how many
laboratories have difficulty in differentiating M. canis and M. audouinii.
Molecular Identification: ITS sequencing is recommended (Gräser et al. 1998, 2000,
Brillowska-Dabrowska et al. 2013).
References: Rebell and Taplin (1970), Rippon (1988), McGinnis (1980), Domsch et
al. (1980), Ajello (1977), Weitzman et al. (1986), Mackenzie et al. (1986), Kane et
al. (1997), de Hoog et al. (2000, 2015), Gräser et al. (1999a, 2008). Cafarchia et al.
(2013).
a
b
(a) Microsporum audouinii showing poor growth on rice grains, usually being
visible only as a brown discolouration. (b) Microsporum canis on rice grains
showing good growth, yellow pigmentation and sporulation.