The curious adventures of Trichophyton equinum in the realm of molecular biology: a modern fairy tale.

Sequence analysis of the highly variable internal transcribed spacer (ITS) regions 1 and 2 of the ribosomal DNA (rDNA) of the nuclear DNA has been used to explore the phylogeny of the dermatophytes. Results have led some investigators to recommend that a number of dermatophyte species be reduced to synonymy with other established species. One such recommendation is that both varieties of the zoophilic dermatophyte Trichophyton equinum be reduced to synonymy with the anthropophilic species T. tonsurans. The morphologies of both species are reviewed, as are their roles in human infection, their physiological characteristics and their respective ecologies. Close examination of these attributes shows clear differences between the varieties of T. equinum and T. tonsurans. The significance of the homogeneity of the ITS sequences of these two dermatophytes is discussed in the context of more recent appraisals of the results of ITS sequencing in other fungi. It is concluded that the results of ITS analysis for both varieties of T. equinum and T. tonsurans are indicative only of common ancestry. Similar arguments could be put forward for rescinding other changes in dermatophyte nomenclature that have been published in recent years.