Trichophyton tonsurans
| Trichophyton tonsurans | |
|---|---|
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| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Eurotiomycetes |
| Order: | Onygenales |
| Family: | Arthrodermataceae |
| Genus: | Trichophyton |
| Species: | T. tonsurans |
| Binomial name | |
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Trichophyton tonsurans Malmsten (1848) |
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Trichophyton tonsurans is a fungus in the family Arthrodermataceae that causes ringworm infection of the scalp. It was first recognized by David Gruby in 1844. Isolates are characterized as the "–" or negative mating type of the Arthroderma vanbreuseghemii complex. This species is thought to be conspecific with T. equinum, although the latter represents the "+" mating strain of the same biological species Despite their biological conspecificity, clones of the two mating types appear to have undergone evolutionary divergence with isolates of the T. tonsurans-type consistently associated with Tinea capitis (particularly in children) whereas the T. equinum-type, as its name implies, is associated with horses as a regular host. Phylogenetic relationships were established in isolates from Northern Brazil, through fingerprinting polymorphic RAPD and M13 markers. There seems to be lower genomic variability in the T. tonsurans species due to allopatric divergence. Any phenotypic density is likely due to environmental factors, not genetic characteristics of the fungus.
Trichophyton tonsurans may be identified through analysis of its fast-growing colonies. Colonies tend to be flat, powdery, and yellow with a reddish undercolour. It develops into a folded colony, and may vary in colour from off-white to grey, with dark pigments that may diffuse into the medium. The younger colonies fluoresce green on Sabouraud's agar, and are also flat, but are mahogany red or lemon-yellow coloured. On this agar the fungus grows peripherally and develops into a flatter, creamy disk with raised edges.Trichophyton tonsurans also produces many inflated, pear-shaped microconidia, borne on matchstick-like stalks. It also forms fewer macroconidia that are 4-6 cells long, with thick cell walls.
A different simple method for identification at early stages is through the detection of chlamydospore-like structures (CLS), which are found on the reverse side of the culture under light microscopy. Chlamydospores are asexual spores that are created through hyphal modification, often with thick cell walls arising from the deposition of hydrophobic materials along the original cell wall. After inoculation on culture media (such as commonly used Mycosel agar), mycelia extend into the media and create the CLS. Normally, strains will produce CLS regardless of the media it is grown on. CLS growth is essentially unaffected by antibiotic treatment with chloramphenicol, as well as by cycloheximide. After 5 days of incubation, CLS production will be evident, suggesting the fungus is highly likely to be T. tonsurans.
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