Pathogenesis of Dermatophytosis: Sensing the Host Tissue.

The genera Trichophyton, Microsporum, and Epidermophyton include filamentous fungi that cause dermatophytosis, a superficial infection of the skin, stratum corneum, nail beds, and hair follicles. The ability of dermatophytes to adhere to these substrates and adapt to the host environment is essential for the establishment of infection. Several fungal enzymes and proteins participate in this adaptive response to the environment and to keratin degradation. Transcription factors such as PacC and Hfs1, as well as heat shock proteins, are involved in sensing and adapting to the acidic pH of the skin in the early stages of fungal-host interaction. During dermatophyte growth, with keratin as the sole carbon source, the extracellular pH shifts from acidic to alkaline. This creates an environment in which most of the known keratinolytic proteases exhibit optimal activity. These events culminate in the establishment and maintenance of the infection, which can be chronic or acute depending on the dermatophyte species. This review focuses on these and other molecular aspects of the dermatophyte-host interaction.