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School of Molecular & Biomedical Science |
Trichophyton sp.Teleomorph: Arthroderma sp.The genus Trichophyton is characterised by the development of both smooth-walled macro- and microconidia. Macroconidia are mostly borne laterally directly on the hyphae or on short pedicels, and are thin- or thick-walled, clavate to fusiform, and range from 4-8 x 8-50 mm in size. Macroconidia are few or absent in many species. Microconidia are spherical, pyriform to clavate or of irregular shape and range from 2-3 x 2-4 mm in size. The presence of microconidia distinguishes this genus from Epidermophyton and the smooth-walled, mostly sessile macroconidia separate it from Microsporum. Twenty species have been recognised, however only the more common species are included in these descriptions. Note: species concepts in dermatophytes are currently in a state of flux. Recent molecular studies have shown that many species appear to be clonal and that there is little correlation between “genetic” and “phenotypic” species (Graser et al. 2006). The descriptions and species concepts provided in this publication are based on traditional morphological criteria which may not correspond to molecular identification results.
MIC data is limited. Antifungal susceptibility testing of individual strains is recommended.
The presence of microconidia distinguishes this genus from Epidermophyton and the smooth-walled, mostly sessile macroconidia separate it from Microsporum. Twenty species have been recognized, however in practice, two groups may be recognized on direct microscopy: In practice, two groups may be recognised on direct microscopy: 1. Those species that usually produce microconidia, macroconidia may or may not be present i.e. T. rubrum, T. interdigitale, T. mentagrophytes, T. equinum, T. erinacei, T. tonsurans, T. terrestre and to a lesser extent T. verrucosum, which may produce conidia on some media; and 2. Those species that usually do not produce conidia. Chlamydospores or other hyphal structures may be present, but microscopy is generally non-diagnostic; i.e. T. verrucosum, T. violaceum, T. concentricum, T. schoenleinii and T. soudanense. Many laboratories seem to have difficulty in distinguishing between species of Trichophyton, especially isolates of T. rubrum, T. interdigitale, T. mentagrophytes and T. tonsurans. Basically, the laboratories which consistently identify these fungi correctly do more work and use additional media and/or confirmatory tests. However, it must be stressed that no one single test is infallible, dermatophyte species are very variable organisms and many characteristics either overlap or are inconsistent. The Mycology Unit at the Adelaide Women’s and Children’s Hospital uses a dermatophyte identification scheme, devised by the late Geraldine Kaminski, comprising 6 different media to help identify and differentiate the various species and strains of Trichophyton. The media in this scheme are Littman Oxgall agar, Lactritmel agar, Sabouraud’s agar with 5% NaCl, 1% Peptone agar, Trichophyton agar No. 1, and hydrolysis of urea (see appendix for details). Kaminski's dermatophyte identification scheme [download pfd file 180 Kb].Practical Identification of Common Dermatophytes [download pdf file 120 Kb]
Clinical significance:The genus Trichophyton contains a number of important species that are the principle causative agents of animal and human dermatophytoses [tinea and ringworm]. 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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