On Sabouraud's dextrose agar, 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, he so called 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 chlamydoconidia are produced in older cultures. Rg-2 organism.
Cultures of Trichophyton tonsurans.
Hyphae, microconidia and macroconidia of T. tonsurans.
Kaminski's Dermatophyte Identification Scheme
Littman Oxgall Agar (Difco): Restricted colony with cream, sometimes greyish, suede-like folded surface with no reverse pigment.
Lactritmel Agar (Mycopathologia 91:57-59, 1985): Macroscopic and microscopic features as described as above for the primary culture.
Sabouraud's Dextrose Agar with 5% NaCl: Very stunted slow growing colony with dark brown surface and reverse.
1% Peptone Agar: Flat, white to cream suede-like surface with raised centre. No reverse pigment.
Hydrolysis of Urea: positive at 5 days.
Nutritional Tests on Trichophyton Agars (Difco): results demonstrate a partial requirement for thiamine.
T. tonsurans showing good growth on T4 agar
indicating a requirement for thiamine.
Hair Perforation Test ("in vitro"): Positive within 14 days.
Trichophyton tonsurans is an anthropophilic fungus with a world wide 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 the Australian Aborigine and African Americans. Invaded hairs show an endothrix infection and do not fluoresce under Wood's ultra-violet light.
Rebell, G., and D. Taplin. 1970. The Dermatophytes. 2nd. revised edition. University of Miami Press, Coral Gables, Florida. USA.
Rippon, J.W. 1988. Medical Mycology. 3rd Edition. W.B. Saunders Co., Philadelphia, USA.