Melanogenesis in dermatophyte species in vitro and during infection

• DOI: 10.1099/mic.0.047928-0
• Publication Date: 2011-05-13T01:16:26Z
• Authors: Sirida Youngchim; Soraya Pornsuwan; Joshua D. Nosanchuk; Wiyada Dankai; Nongnuch Vanittan...
• Keywords: Melanins; 0301 basic medicine; 0303 health sciences; Virulence Factors; Epidermophyton; Laccase; Electron Spin Resonance Spectroscopy; Hyphae; Fluorescent Antibody Technique; Spores, Fungal; Culture Media; 3. Good health; 03 medical and health sciences; Trichophyton; Dermatomycoses; Humans; Microsporum; Benzothiazoles; Sulfonic Acids

Dermatophytes are keratinophilic fungi that are the most common cause of fungal skin infections worldwide. Melanin has been isolated from several important human fungal pathogens, and the polymeric pigment is now recognized as an important virulence determinant. This study investigated whether dermatophytes, includingTrichophyton rubrum,Trichophyton mentagrophytes,Epidermophyton floccosumandMicrosporum gypseum,produce melanin or melanin-like compoundsin vitroand during infection. Digestion of the pigmented microconidia and macroconidia of dermatophytes with proteolytic enzymes, denaturant and hot concentrated acid yielded dark particles that retained the size and shape of the original fungal cells. Electron spin resonance spectroscopy revealed that particles derived from pigmented conidia contained a stable free radical signal, consistent with the pigments being a melanin. Immunofluorescence analysis demonstrated reactivity of a melanin-binding mAb with the pigmented conidia and hyphae, as well as the isolate particles. Laccase, an enzyme involved in melanization, was detected in the dermatophytes by an agar plate assay using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as the substrate. Skin scrapings from patients with dermatophytoses contained septate hyphae and arthrospores that were reactive with the melanin-binding mAb. These findings indicate that dermatophytes can produce melanin or melanin-like compoundsin vitroand during infection. Based on what is known about the function of melanin as a virulence factor of other pathogenic fungi, this pigment may have a similar role in the pathogenesis of dermatophytic diseases.