DESCRIPTIONS OF MEDICAL FUNGI

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Descriptions of Medical Fungi
Trichophyton Malmsten
Rippon (1988) accepted 22 species and four varieties in the genus Trichophyton based
on morphology. DNA sequences now play a prominent role in delineating phylogenetic
relationships, and as such species concepts in Trichophyton have changed. Sixteen
species are now recognised in the genus. The descriptions and species concepts
provided in this publication are based upon a combination of traditional morphological
criteria and the current (2016) recognised phylogenetic species (de Hoog et al. 2016).
The genus Trichophyton is characterised morphologically 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 µm 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 µm in size. The presence of microconidia differentiates this genus from
Epidermophyton, and the smooth-walled, mostly sessile macroconidia differentiates it
from Lophophyton, Microsporum and Nannizzia.
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.
eriotrephon, T. tonsurans, and to a lesser extent T. verrucosum, which may produce
conidia on some media. In these species the shape, size and arrangement of the
microconidia is the most important character. Culture characteristics are also useful.
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.
Culture characteristics and clinical information such as the site, appearance of the
lesion, geographic location, travel history, animal contacts and even occupation are
most important.
Many laboratories have used growth on additional media and/or confirmatory tests to
help differentiate between species of Trichophyton, especially isolates of T. rubrum, T.
interdigitale, T. mentagrophytes and T. tonsurans. These include growth characteristics
on media such as Littman oxgall agar, lactritmel agar, potato dextrose agar, Sabouraud’s
agar with 5% Salt, 1% peptone agar, bromocresol purple-milk solids glucose agar
(BCP), Trichophyton agars No. 1-5, hydrolysis of urea and hair perforation tests.
Molecular Identification: ITS and EF-1α sequencing is recommended for accurate
species identification (Gräser et al. 1998, 1999b, 2000a, 2008; Irinyi et al. 2015;
Mirhendi et al. 2015).
MALDI-TOF MS: Methods reported by Erhard et al. (2008), Nenoff et al. (2011),
Cassange et al. (2011), l’Ollivier et al. (2013), Calderaro et al. (2014), Packeu et al.
(2013, 2014).
References: Rebell and Taplin (1970), Ajello (1972), Vanbreusegham et al. (1978),
Rippon (1988), McGinnis (1980), Domsch et al. (1980), Kane et al. (1997), Chen et al.
(2011), de Hoog et al. (2000, 2015, 2016).