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School of Molecular & Biomedical Science |
Trichophyton violaceumOn Sabouraud's dextrose agar, colonies are very slow growing, glabrous or waxy, heaped and folded and a deep violet in colour. Cultures often become pleomorphic, forming white sectors and occasional non-pigmented strains may occur. Hyphae are relatively broad, tortuous, much branched and distorted. Young hyphae usually stain well in lactophenol cotton blue, whereas older hyphae stain poorly and show small central fat globules and granules. No conidia are usually seen, although occasional pyriform microconidia have been observed on enriched media. Numerous chlamydoconidia are usually present, especially in older cultures. RG-2 organism.
Nutritional requirements: T. violaceum has a partial nutrient requirement for thiamine. There is minimal growth on casein vitamin-free agar (Trichophyton Agar No. 1), and slightly better growth on vitamin-free agar plus thiamine (Trichophyton Agar No. 4). The partial requirement for thiamine separates this organism from T. gourvillii, T. rubrum, and other species that may produce purple pigmented colonies.
Clinical significance:Trichophyton violaceum is an anthropophilic fungus causing inflammatory or chronic non-inflammatory finely scaling lesions of skin, nails, beard and scalp, producing the so-called "black dot" tinea capitis. Distribution is world-wide, particularly in the Near East, Eastern Europe, USSR and North Africa. Invaded hairs show an endothrix infection and do not fluoresce under Wood's ultra-violet light. Mycosis: DermatophytosisFurther reading: Rippon, J.W. 1988. Medical Mycology. 3rd Edition. W.B. Saunders Co., Philadelphia, USA.
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