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School of Molecular & Biomedical Science |
Trichophyton mentagrophytesOn Sabouraud's dextrose agar, colonies are generally flat, white to cream in colour, with a powdery to granular surface. Some cultures show central folding or develop raised central tufts or pleomorphic suede-like to downy areas. Reverse pigmentation is usually a yellow-brown to reddish-brown colour. Numerous single-celled microconidia are formed, often in dense clusters. Microconidia are hyaline, smooth-walled, and are predominantly spherical to subspherical in shape, however occasional clavate to pyriform forms may occur. Varying numbers of spherical chlamydoconidia, spiral hyphae and smooth, thin-walled, clavate shaped, multicelled macroconidia may also be present.
Kaminski's Dermatophyte Identification Scheme:Littman Oxgall Agar (Difco): Raised greyish-white, suede-like to downy colony. Some cultures may show a diffusible yellow to brown pigment. Lactritmel Agar (Mycopathologia 91:57-59, 1985): Cultures are flat, white to cream in colour, with a powdery to granular surface. Some cultures develop raised central tuft or pleomorphic downy areas. Reverse pigmentation is yellow-brown to pinkish-brown to red-brown. Microscopic morphology similar to that described above, with predominantly spherical microconidia, often forming in dense clusters, and varying numbers of spherical chlamydoconidia, spiral hyphae and smooth, thin-walled, clavate, multiseptate macroconidia. Sabouraud's Dextrose Agar with 5% NaCl: Cultures are heaped and folded, buff to brown in colour, with a suede-like surface texture and characteristically have a very dark reddish-brown submerged peripheral fringe and reverse pigmentation. 1% Peptone Agar: Flat, cream coloured, powdery to granular colonies with no reverse pigment. Hydrolysis of Urea: Positive within 7 days (usually 3 to 5 days). Vitamin Free agar (Difco Trichophyton Agar No.1): Good growth indicating no special nutritional requirements. Cultures are flat, cream coloured, with a powdery to suede-like surface, and have a reddish-brown reverse pigmentation. Hair Perforation Test ("in vitro"): Positive within 14 days. T. mentagrophytes, (granular variety or zoophilic form are not acceptable varietal names) can be distinguished from other T. intergigitale by (a) its granular appearance on the 1% Peptone agar, (b) it's microscopic morphology of more spherical microconidia and generally greater numbers of macroconidia and (c) a yellow to brown diffusible pigment is often seen on the Littman Oxgall agar. Clinical significance:T. mentagrophytes is the zoophilic form of T. mentagrophytes with a world-wide distribution and a wide range of animal hosts including mice, guinea-pigs, kangaroos, cats, horses, sheep and rabbits. Produces inflammatory skin or scalp lesions in humans, particularly in rural workers. Kerion of the scalp and beard may occur. Invaded hairs show an ectothrix 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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