DESCRIPTIONS OF MEDICAL FUNGI
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200<br />
Descriptions of Medical Fungi<br />
Synonymy: T. mentagrophytes var. interdigitale (Priestley) Moraes, Anais Bras.<br />
Trichophyton interdigitale is an anthropophilic fungus which is a common cause of<br />
tinea pedis, particularly the vesicular type, tinea corporis, and sometimes superficial<br />
nail plate invasion in humans. It is not known to invade hair in vivo but produces hair<br />
perforations in vitro. Distribution is worldwide. This species may be regarded as a<br />
clonal offshoot of the zoophilic T. mentagrophytes (de Hoog et al. 2016).<br />
RG-2 organism.<br />
Morphological Description: Colonies are usually flat, white to cream in colour with<br />
a powdery to suede-like surface and yellowish to pinkish brown reverse pigment,<br />
often becoming a darker red-brown with age. Numerous subspherical to pyriform<br />
microconidia, occasional spiral hyphae and spherical chlamydospores are present,<br />
the latter being more abundant in older cultures. Occasional slender, clavate, smoothwalled,<br />
multiseptate macroconidia are also present in some cultures.<br />
Confirmatory Tests:<br />
Littman Oxgall Agar: Raised white downy colony with no reverse pigment.<br />
Lactritmel Agar: Macroscopic and microscopic features as described above.<br />
Sabouraud’s Dextrose Agar with 5% Salt: Heaped and folded, buff-coloured, suedelike<br />
surface with a dark reddish-brown submerged fringe and brown reverse.<br />
1% Peptone Agar: Flat, white to cream, suede-like surface with raised white downy<br />
centre. No reverse pigment.<br />
Vitamin Free Agar (Trichophyton Agar No.1): Good growth indicating no special<br />
nutritional requirements, flat cream powdery surface with central downy tuft. Reverse<br />
pale pinkish-brown.<br />
Hydrolysis of Urea: Positive within 7 days (usually 3 to 5 days).<br />
Hair Perforation Test: Positive.<br />
Trichophyton interdigitale Priestley<br />
Key Features: Culture characteristics, microscopic morphology and in vitro perforation<br />
of human hair.<br />
Trichophyton interdigitale can be distinguished from T. rubrum and T. mentagrophytes<br />
by: (a) its culture characteristics and microscopic morphology on SDA and/or lactritmel<br />
agar; (b) its growth and colony morphology on Sabouraud’s salt agar (colonies of T.<br />
interdigitale and T. mentagrophytes unlike T. rubrum, grow very well on this medium<br />
and usually produce a distinctive dark reddish-brown reverse pigment); (c) a positive<br />
urease test (within 7 days), a positive hair perforation test and the production of a<br />
yellow-brown to pinkish-brown reverse pigment on pigment stimulation media like<br />
lactritmel and Trichophyton No.1 agars; (d) T. interdigitale demonstrates profuse growth<br />
and alkalinity on BCP milk solids agar; (e) on 1% peptone agar T. interdigitale has a<br />
suede-like to downy surface whereas T. mentagrophytes has a characteristic granular<br />
appearance.