Species Distinction in the Trichophyton rubrum Complex

Area of Science:

• Medical Mycology
• Molecular Taxonomy
• Dermatophytosis

Background:

• The Trichophyton rubrum species complex comprises globally distributed dermatophytic fungi.
• Members exhibit distinct phenotypes and clinical symptoms despite high genomic similarity.
• Accurate species delimitation is crucial for understanding disease transmission and treatment.

Purpose of the Study:

• To reestablish a natural species concept for the Trichophyton rubrum complex.
• To differentiate between T. rubrum, T. soudanense, and T. violaceum using combined molecular, phenotypic, and physiological data.
• To evaluate the utility of various methods for routine diagnostics.

Main Methods:

• Internal transcribed spacer (ITS) ribosomal DNA sequencing.
• Analysis of colony appearance, microscopy, and physiological characteristics (keratinase activity, lipophilicity).
• Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and amplified fragment length polymorphism (AFLP).

Main Results:

• Three distinct groups corresponding to T. rubrum, T. soudanense, and T. violaceum were identified using ITS sequencing.
• Phenotypic and physiological differences were observed between groups but were not diagnostic.
• MALDI-TOF MS and AFLP showed partial consistency with ITS data but lacked unambiguous species discrimination.
• T. soudanense appears phenotypically and genotypically intermediate.

Conclusions:

• T. rubrum, T. soudanense, and T. violaceum are considered independent species with distinct geographical distributions and clinical associations.
• ITS sequencing is the recommended method for routine diagnostics of this species complex.
• Further research may refine understanding of their ecological and clinical roles.