Melanogenesis in dermatophyte species in vitro and during infection

Abstract

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, including Trichophyton rubrum, Trichophyton mentagrophytes, Epidermophyton floccosum and Microsporum gypseum, produce melanin or melanin-like compounds in vitro and 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 2,29-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 compounds in vitro and 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. INTRODUCTIONDermatophytes are highly specialized pathogenic fungi that cause dermatophytosis, superficial infections of the skin, hair and nails. These keratinophilic organisms cause disease by inducing host inflammation in response to fungal metabolic by-products (Ellis et al., 2000). The aetiological agents are from three genera, Trichophyton, Microsporum and Epidermophyton, based on the formation and morphology of their conidia (structures of asexual reproduction). According to their host preference and natural habitat, dermatophytes are generally grouped in three categories, anthropophilic (human), zoophilic (animal) and geophilic (soil). Dermatophytosis is among the most prevalent infections in the world, causing more than 20 % of these infections according to the World Health Organization (Marques, et al., 2000). Dermatophytes thrive at surface temperatures of 25-28 u C and skin mycosis is supported by warm and humid conditions. Due to these circumstances, superficial fungal infections are relatively common in tropical and subtropical countries where the hot climate and humid weather is favourable for the acquisition and maintenance of the disease (Hiruma & Yamaguchi, 2003). In Thailand, the incidence of dermatophyte infections is 38.1 % for onychomycosis and 42.1 % for tinea pedis compared with other fungal infections (Ungpakorn, 2005). In addition, Trichoph...

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“…The conidia become heavily pigmented during maturation due to increased deposition of the DHN melanin (Fig. 1B) (21,45,46). To examine the expression pattern of abr1 and abr2 genes, we collected wild-type A. fumigatus samples at 12 h (vegetative hyphae), 24 h (competent hyphae), 36 h (early conidiophores), and 48 h (conidiophores with mature conidia) ( Fig.…”

The Role of L-DOPA on Melanization and Mycelial Production in Malassezia Furfur

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Efficiency of methylene blue‐mediated photodynamic therapy vs intense pulsed light in the treatment of onychomycosis in the toenails

“…Q‐switched Nd:YAG laser at 1064 nm showed also inhibitory effect on the colonies treated. It is known that Trichophyton species contain melanin in their cell wall, and it selectively absorbs this wavelength …”