The New Species Concept in Dermatophytes—a Polyphasic Approach

Abstract

The dermatophytes are among the most frequently observed organisms in biomedicine, yet there has never been stability in the taxonomy, identification and naming of the approximately 25 pathogenic species involved. Since the identification of these species is often epidemiologically and ethically important, the difficulties in dermatophyte identification are a fruitful topic for modern molecular biological investigation, done in tandem with renewed investigation of phenotypic characters. Molecular phylogenetic analyses such as multilocus sequence typing have had to be tailored to accommodate differing the mechanisms of speciation that have produced the dermatophytes that are commonly seen today. Even so, some biotypes that were unambiguously considered species in the past, based on profound differences in morphology and pattern of infection, appear consistently not to be distinct species in modern molecular analyses. Most notable among these are the cosmopolitan bane of nails and feet, Trichophyton rubrum, and the endemic African agent of childhood tinea capitis, Trichophyton soudanense, which are effectively inseparable in all analyses. The molecular data require some reinterpretation of results seen in conventional phenotypic tests, but in most cases, phylogenetic insight is readily integrated with current laboratory testing procedures.

Correlation Between Phenotypic and Genotypic Identification of Trichophyton Violaceum

“…Gräser et al in 2008 6 described three prominent phenotypes of T. violaceum : (1) classic pan-African and west/central Asian T. violaceum, consisting of dense, slow-growing and glabrous (this combination of characters is called "faviform"), predominantly blood-red colonies, sometimes with whitish sectors, and with a uniform stimulation response to thiamine; (2) isolates corresponding to the T. violaceum synonym "T. glabrum," similar to typical T. violaceum except whitish in color, mostly coming from the Horn of Africa region (Eritrea and Somalia); and (3) central African isolates corresponding to the synonym "T. yaoundei" which are faviform and whitish but often secrete a brown pigment into surrounding Sabouraud glucose agar.…”

Genetic relationships and isozyme profile of dermatophytes and Candida strains from Egypt and Libya

“…Conventional methods on the basis of phenotype variations and molecular methods on the basis of molecular differences were used for identification of dermatophytes species. Due to some limitations in traditional methods such as the high degree of phenoltypic similarity between these relative species identification and time-consumption, many isolates reveal unusual characteristics (Weiyzman et al, 1995;Graser et al, 2008;Shehata et al, 2008;De Baere et al, 2010). To overcome these problems, in recent years, molecular marker approaches relying on genetic makeup are regarded as useful in the exact and rapid recognition of dermatophytes Kanbe et al, 2003;Liu et al, 2000;Graser et al, 1998).…”

Fungi on the Skin: Dermatophytes and Malassezia

“…Dermatophytes are ascomycetes with septate hyphae, most closely related to Coccidioides immitis within the Onygenales (Kwon-Chung and Bennett 1992; Graser et al 2008). There are three genera of dermatophytes, Trichophyton, Microsporum, and Epidermophyton.…”