A recent multilocus phylogenetic study on the taxonomy of the dermatophytes has recognised 21 species of Arthroderma (de Hoog et al. 2016). Colonies mostly granular to cottony, yellowish to brownish, with a cream-coloured or brown colony reverse. Macroconidia are multicelled, (sub)hyaline, clavate, fusiform or cigar-shaped and are thick- and rough-walled. Microconidia are hyaline, 1-celled, clavate and smooth-walled.
Note: Trichophyton ajelloi and T. terrestre have now been transferred to the genus Arthroderma.
- Arthroderma insingulare complex
Arthroderma insingulare is a geophilic fungus of worldwide distribution which may occur as a saprophytic contaminant on humans and animals. Durie and Frey (1957) first described this soil fungus as Trichophyton terrestre from New South Wales, Australia. Since then T. terrestre has been described as an anamorph of three different species of Arthroderma; A. insingulare, A. lenticulare and A. quadrifidum (Padhye and Carmichael, 1972). However, ITS and D1/D2 sequencing of the original isolates obtained from the Mycology Laboratory at Royal North Shore Hospital, Sydney has now identified this fungus as Arthroderma insingulare.
Colonies are usually flat to downy with a suede-like to granular texture resembling T. mentagrophytes. The surface colour may range from white to cream, buff to yellow, or greenish-yellow. Reverse pigmentation is usually yellowish-brown although some variants have a deep rose red reverse. Microconidia are large, clavate or pedicellate, usually exhibiting transition forms to more or less abundant lateral macroconidia. Macroconidia are clavate to cylindrical with rounded ends, smooth and thin-walled, and are two to six-celled. Chlamydospores, hyphal spirals, racquet mycelium and antler hyphae may also be present. No growth at 37C.
ITS and D1/D2 sequencing is recommended for definitive identification of isolates.
- Arthroderma uncinatum complex
Arthroderma uncinatum is a geophilic fungus with a worldwide distribution which may occur as a saprophytic contaminant on humans and animals but infections are doubtful. Not known to invade hair in vivo, but produces hair perforations in vitro.
Colonies are usually flat, powdery, cream, tan to orange-tan in colour, with a blackish-purple submerged fringe and reverse. Macroconidia are numerous, smooth, thick-walled, elongate, cigar-shaped, 29-65 x 5-10 µm, and multiseptate with up to nine or ten septa. Microconidia are usually absent, but when present are ovate to pyriform in shape.