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School of Molecular & Biomedical Science |
Microsporum canis var. equinumBasionym: Microsporum equinum (Delacroix & Bodin) Gueguen Microsporum equinum is now considered to be a genotypic synonym of Microsporum canis (de Hoog et al. 2000), however we propose it be maintained as a variety of M. canis due to phenotypic and epidemiologic differences. Colonies are flat, spreading, suede-like, pale buff to pale salmon, usually with some radial furrows. A buff to pinkish-buff to yellow-brown reverse pigment is produced. Note: only a few strains produce conidia on primary isolation, however growth on urea agar usually stimulates the production of macroconidia. Macroconidia are small (especially when compared to those produced by M. canis), broad, irregular, spindle-shaped, 18-60 x 5-15 mm with rough thick walls and few septa. Microconidia are pyriform to clavate in shape, 3-9 x 1.5-3.5 mm, but are rarely produced. RG-2 organism.
Growth on Rice Grains: Poor with minimal surface growth, usually being visible only as a brown discolouration. This is one of the features which distinguish M. canis var. equinum from M. canis. Reverse Pigment on Potato Dextrose Agar: Salmon to pinkish-brown (M. canis is bright yellow). Lactritmel Agar: Colonies are usually flat, spreading, with a fine, whitish suede-like surface and a very pale yellow-brown reverse. Microscopic morphology as described above. Vitamin Free Agar (Trichophyton Agar No.1): Good growth indicating no special nutritional requirements. Cultures are flat, white, suede-like to downy, with a yellow-brown reverse. Hair Perforation Test: Negative after 28 days. Key Features: macroconidial shape and size, inability to perforate hair in vitro, and poor growth on polished rice grains. Clinical significance:Microsporum equinum is a rare cause of ringworm of horses. Invaded hairs show an ectothrix infection and fluoresce a bright greenish-yellow under Wood's ultra-violet light. Rarely infects man or other animal species. Reported from Australia, Europe and North America. Mycosis: DermatophytosisFurther 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.
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