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School of Molecular & Biomedical Science |
Trichophyton concentricumOn Sabouraud's dextrose agar, colonies are slow growing, raised and folded, glabrous becoming suede-like, mostly white to cream coloured, but sometimes orange-brown coloured, often deeply folded into the agar which may produce splitting of the medium in some cultures. Reverse is buff to yellow-brown to brown in colour. Cultures consist of broad, much-branched, irregular, often segmented, septate hyphae which may have "antler" tips resembling T. schoenleinii. Chlamydoconidia are often present in older cultures. Microconidia and macroconidia are not usually produced, although some isolates will produce occasional clavate to pyriform microconidia. Note hyphal segments may artificially resemble macroconidia.
Kaminski's Dermatophyte Identification SchemeLittman Oxgall Agar (Difco): Small, heaped and folded, blue-grey, suede to glabrous colonies with no reverse or diffusible pigment. Lactritmel Agar (Mycopathologia 91:57-59, 1985): Colonies tend to be flatter, dull-white, suede-like, almost glabrous with a yellow-brown reverse pigment. Microscopic morphology is similar to that described above, however occasional clavate to pyriform microconidia are usually present. Note occasional, small, slender, smooth thin-walled macroconidia with 2-3 septa have been reported on specialized media like lactritmel agar, bean pod agar and hay infusion agar. Sabouraud's Dextrose Agar with 5% NaCl: Small, stunted, heaped and folded, cream to buff, glabrous colonies with no reverse pigment. 1% Peptone Agar: Flat, white, suede-like colony with a pale yellow-brown reverse. Hydrolysis of Urea: Negative after 7 days. Vitamin Free agar (Difco Trichophyton Agar No.1): Growth occurs on vitamin free agar (T1) but is usually slightly better on media containing thiamine i.e. T3 = T1 + thiamine and inositol, and T4 = T1 + thiamine. The slight enhancement of growth in the presence of thiamine helps to distinguish T. concentricum from T. schoenleinii, although this does not occur in all strains. Hair Perforation Test ("in vitro"): Negative at 28 days. Clinical significance:Trichophyton concentricum is an anthropophilic fungus which causes chronic widespread non-inflammatory tinea corporis known as tinea imbricata because of the concentric rings of scaling it produces. It is not known to invade hair. Infections among Europeans are rare. Distribution is restricted to the Pacific Islands of Oceania, South East Asia and Central and South America. Mycosis: DermatophytosisFurther reading:Rippon, J.W. 1988. Medical Mycology. 3rd Edition. W.B. Saunders Co., Philadelphia, USA
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