Dermatophytes as Saprophytes and Pathogens

Dermatophytes infect the stratum corneum, nails and hair and are the most common agents of superficial mycoses in humans and animals. At present the genome of seven species has been sequenced. Between 22.5 and 24 Mb, the dermatophyte genomes are smaller in size than those of Coccidioides spp., Histoplasma spp. and Aspergillus spp. They are enriched for particular families of genes encoding secreted proteases, fungal specific kinases and proteins containing the LysM domain that is known to bind chitin. Different tools were recently developed to improve genetic analyses of dermatophytes, including efficient systems for targeted gene inactivation, gene silencing and broad transcriptional profiling techniques. Unexpectedly, gene expression profiles in the skin and hair of infected guinea pigs were found to be very different from those during in vitro growth using hard keratin as a substrate. Instead of the major in vitro expressed protease genes, others were found to only be activated in the skin of infected animals. In other words, the expression of putative virulence genes in dermatophytoses is more complex than previously assumed and likely depends on the site and type of infection. Further broad transcriptional profiling approaches during infections will give new insights into the pathogenic mechanisms of dermatophytes.