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Trichophyton tonsurans
''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.〔
==Colony morphology==
''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''.〔
Responses of ''T. tonsurans'' to different growth conditions and nutrient media is useful in aiding identification. For example, growth is enhanced in the presence of thiamine,〔 and this exogenous requirement for thiamine distinguishes ''T. tonsurans'' from similar species.〔 Since thiamine stimulates growth, ''T. tonsurans'' also displays this behaviour on vitamin-free, thiamine-supplemented casamino acids agar but the growth is more sparse, and subsurface growth is absent.〔 BCP-milk solids glucose agar can also be used as an indicator of this fungus. This medium turns from pale blue to purple in colour in 7–14 days of growth at . The colour change is due to an alkaline shift arising from the release of ammonium during protein hydrolysis.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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