DESCRIPTIONS OF MEDICAL FUNGI

Descriptions of Medical Fungi 213
Trichophyton tonsurans is an anthropophilic fungus with a worldwide distribution which
causes inflammatory or chronic non-inflammatory finely scaling lesions of skin, nails
and scalp. It is a common cause of tinea capitis in Australian Aborigines and African
Americans. Invaded hairs show an endothrix infection and do not fluoresce under
Wood’s ultra-violet light.
RG-2 organism.
Morphological Description: Colonies show considerable variation in texture and
colour. They may be suede-like to powdery, flat with a raised centre or folded, often
with radial grooves. The colour may vary from pale-buff to yellow, (the sulfureum form
which resembles Epidermophyton floccosum), to dark-brown. The reverse colour
varies from yellow-brown to reddish-brown to deep mahogany. Hyphae are relatively
broad, irregular, much branched with numerous septa. Numerous characteristic
microconidia varying in size and shape from long clavate to broad pyriform, are borne
at right angles to the hyphae, which often remain unstained by lactophenol cotton blue.
Very occasional smooth, thin-walled, irregular, clavate macroconidia may be present
on some cultures. Numerous swollen giant forms of microconidia and chlamydospores
are produced in older cultures.
Confirmatory Tests:
Mycosel Agar: Chlamydospore-like structures produced by 5 days is characteristic of
T. tonsurans (Mochizuki et al. 2013).
Hydrolysis of Urea: positive at 5 days.
Trichophyton tonsurans Malmsten
T1
T4
a
b
Nutritional Tests on Trichophyton Agars: results demonstrate a partial requirement
for (a) thiamine. T1 = vitamin free agar, (b) T4 = vitamin free + thiamine agar.
Hair Perforation Test: Positive within 14 days.
Key Features: microscopic morphology, culture characteristics, endothrix invasion of
hairs and partial thiamine requirement.
References: Rebell and Taplin (1970), Ajello (1972), Vanbreusegham et al. (1978),
Rippon (1988), McGinnis (1980), Domsch et al. (1980), Kane et al. (1997) and de
Hoog et al. (2000, 2015).