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School of Biological Sciences
The University of Adelaide

Dr David Ellis

Microsporum nanum

Teleomorph: Arthroderma obtusum

Colonies are flat, cream to buff in colour with a suede-like to powdery surface texture. Young colonies have a brownish-orange pigment which deepens into a dark reddish-brown with age. Cultures produce numerous small ovoid to pyriform macroconidia with 1-3 cells, but mostly 2 cells, with relatively thin, finely echinulate (rough) walls, and broad truncate bases. Many macroconidia are borne on conidiophores (stalks) which do not stain readily. Occasional clavate microconidia are present, which distinguishes M. nanum from some species of Chrysosporium.  RG-2 organism.

Microsporum nanun infection of pigs.

Culture of Microsporum nanum
Culture of Microsporum nanum.

Macroconidia of M. nanum
Macroconidia of M. nanum.

Clinical significance:

Microsporum nanum is a geophilic and zoophilic fungus frequently causing chronic non-inflammatory lesions in pigs and a rare cause of tinea in humans. Also present in soil of pig-yards. Infections in man usually contacted directly from pig or fomites. Invaded hairs may show a sparse ectothrix or endothrix infection but do not fluoresce under Wood's ultra-violet light. The geographical distribution is world-wide.

Mycosis: Dermatophytosis

Further reading:

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