Molecular differentiation of dermatophyte fungi.

Our previous studies of the ribosomal DNA variation in dermatophytes have shown that these fungi are monophyletic in origin. However, this approach did not allow us to differentiate all the species defined by classical means. Therefore, we studied the internal transcribed spacer 1 (ITS 1) region of 17 species of the fungal order Onygenales, comprising the pathogenic keratinophilic fungi. Interspecific nucleotide composition and sequence length variation of the ITS 1 region was high, mean identities were as low as 40% and sequence lengths varied from 169 to 293 basepairs. Each established dermatophyte species could be identified. In contrast, the flanking sequences at the 3' end of 18S and the 5.8S rDNA were conserved. Although the value of the ITS 1 region as a phylogenetic tool may be limited because of its high variability, it provides the information necessary to design species-specific probes, or polymerase chain reaction restriction fragment polymorphism systems useful for taxonomic or rapid diagnostic tests.