DESCRIPTIONS OF MEDICAL FUNGI

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Descriptions of Medical Fungi
Trichophyton equinum (Matruchot & Dassonville) Gedoelst
Synonomy: Trichophyton equinum var. autotrophicum J.M.B. Smith et al.
Trichophyton equinum is a zoophilic fungus causing ringworm in horses and rare
infections in humans. It has a worldwide distribution except for the autotrophicum strain
which is restricted to Australia and New Zealand. Invaded hairs show an ectothrix
infection but do not fluoresce under Wood’s ultra-violet light.
RG-2 organism.
Morphological Description: Colonies are usually flat, but some may develop gentle
folds or radial grooves, white to buff in colour, suede-like to downy in texture, and are
similar to T. mentagrophytes. Cultures usually have a deep-yellow submerged fringe
and reverse which later becomes dark red in the centre. Microscopically: abundant
microconidia which may be clavate to pyriform and sessile or spherical and stalked
are formed laterally along the hyphae. Macroconidia are only rarely produced, but
when present are clavate, smooth, thin-walled and of variable size. Occasional nodular
organs may be present and the microconidia often undergo a transformation to produce
abundant chlamydospores in old cultures.
Confirmatory Tests:
Lactritmel Agar: Flat spreading, white to cream-coloured, powdery to granular surface
with a central downy papilla, and deep brownish-red reverse. Microscopic morphology
as described above.
Hydrolysis of Urea: Positive in 4-5 days.
a
b
Nutritional Tests on Trichophyton Agars: (a) Most strains require nicotinic acid for
growth except those from Australia and New Zealand, which are autotrophic (b). T1 =
vitamin free agar, T5 = vitamin free + nicotinic acid agar.
Hair Perforation Test: Negative; but positive for the autotrophicum strains.
Molecular Diagnostics: Species identification supported by ITS sequencing (Gräser
et al. 1999a; Chen et al. 2011).
Key Features: Microscopic morphology, culture characteristics, nicotinic acid
requirement and clinical lesions in horses. Most strains require nicotinic acid for growth
except autotrophic strains.