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School of Molecular & Biomedical Science |
Trichophyton rubrum granular strainOn Sabouraud's dextrose agar, colonies are flat to slightly raised, white to cream, suede-like with a pinkish-red reverse. Microscopically, most cultures have numerous clavate to pyriform microconidia and moderate numbers of smooth, thin walled multiseptate, slender cylindrical macroconidia. Older cultures may show numerous chlamydospores with few clavate to pyriform microconidia.
Kaminski's Dermatophyte Identification Scheme:Littman Oxgall Agar (Difco): Raised, greyish, suede-like colonies with some radial folding and a greenish-yellow diffusible pigment. Lactritmel Agar (Mycopathologia 91:57-59, 1985): Flat, white to rose pink, suede-like to granular colonies with a pinkish to wine-red reverse. Numerous broad clavate to pyriform microconidia and moderate numbers of smooth, thin-walled, slender cylindrical macroconidia are present. A few chlamydospores may be present in older cultures. Sabouraud's Dextrose Agar with 5% NaCl: A very stunted, heaped and folded, glabrous, cream thallus, later developing a dark red central spot. Reverse is a brownish-yellow colour. 1% Peptone Agar: Flat, white to cream, glabrous to suede-like colony with no reverse pigment. Hydrolysis of Urea: Positive at 7 days Vitamin Free agar (Difco Trichophyton Agar No.1): Good growth indicating no special nutritional requirements. Culture shows white to cream suede-like colonies with a pinkish-red to wine-red reverse. Hair Perforation Test ("in vitro"): Positive. The above morphological and cultural characteristics are typical of Trichophyton rubrum granular type. Two other strains or varieties of the T. rubrum granular type have been recognized. 1. T. rubrum var. rhodainiiMicroscopically similar to granular type except many of the thin-walled macroconidia often show terminal appendages. Colonies are characteristically hyperpigmented with a violet to red-violet, heaped and folded, glabrous surface and a deep red-violet reverse 2. T. rubrum African typeMicroscopically similar to granular strains, except the macroconidia usually have terminal appendages. Colonies are powdery and will produce characteristic wine-red reverse pigmentation on pigment stimulating media. May or may not show characteristic red reverse pigment on primary isolation media. Clinical significance:Trichophyton rubrum granular strain is a frequent cause of tinea corporis in South East Asia and in Aborigines living in the Northern Territory of Australia. However, since the Vietman War, it has been spread throughout the world, especially to those countries with returning troops or to those receiving refugees, where it has often been described as a new species. The granular strain of T. rubrum represents the parent strain of T. rubrum downy type; the later evolved by establishing a niche in feet (tinea pedis) when the former was imported into Europe around the turn of the century. It should be stressed that intermediate strains between the two types do occur and that many culture and morphological characteristics overlap. Invaded hairs show ectothrix or endothrix infection but do not fluoresce under Wood's ultra-violet light. 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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