The Malassezia genus in skin and systemic diseases

Abstract

In the last 15 years, the genus Malassezia has been a topic of intense basic research on taxonomy, physiology, biochemistry, ecology, immunology, and metabolomics. Currently, the genus encompasses 14 species. The 1996 revision of the genus resulted in seven accepted taxa: M. furfur, M. pachydermatis, M. sympodialis, M. globosa, M. obtusa, M. restricta, and M. slooffiae. In the last decade, seven new taxa isolated from healthy and lesional human and animal skin have been accepted: M. dermatis, M. japonica, M. yamatoensis, M. nana, M. caprae, M. equina, and M. cuniculi. However, forthcoming multidisciplinary research is expected to show the etiopathological relationships between these new species and skin diseases. Hitherto, basic and clinical research has established etiological links between Malassezia yeasts, pityriasis versicolor, and sepsis of neonates and immunocompromised individuals. Their role in aggravating seborrheic dermatitis, dandruff, folliculitis, and onychomycosis, though often supported by histopathological evidence and favorable antifungal therapeutic outcomes, remains under investigation. A close association between skin and Malassezia IgE binding allergens in atopic eczema has been shown, while laboratory data support a role in psoriasis exacerbations. Finally, metabolomic research resulted in the proposal of a hypothesis on the contribution of Malassezia-synthesized aryl hydrocarbon receptor (AhR) ligands to basal cell carcinoma through UV radiation-induced carcinogenesis.

Fig 1

Pityriasis versicolor in a 42-year-old female patient. The patient had relapsing disease for the past 6 years.

Fig 2

Histopathology of noninflammatory pityriasis versicolor. Shown is the infiltration of the hyperkeratotic stratum corneum by Malassezia cells and hyphae; there is a distinct absence of an inflammatory cell infiltrate. (A) Hematoxylin-eosin stain; (B) PAS stain. Original magnification, ×200.

Fig 3

Histopathology of inflammatory pityriasis versicolor. Shown is the infiltration of the hyperkeratotic stratum corneum by Malassezia cells and hyphae; there is a moderately dense perivascular inflammatory cell infiltrate in the upper dermis. (A) Hematoxylin-eosin stain; (B) PAS stain. Original magnification, ×200.

Fig 4

Seborrheic dermatitis in the nasolabial folds. The distribution of the lesions is typical; however, the seborrheic dermatitis can be characterized as severe, as the disease is extended into the parietal region and is associated with intense erythema and scaling.

Fig 5

Malassezia folliculitis in a 34-year-old construction worker. The condition developed after working in a hot, humid environment for a few days. (A) Back of the patient. (B) Close-up view of the lesions.

Fig 6

Histopathology of Malassezia folliculitis. (A) Dilated hair follicle filled with keratinous material and basophilic debris. Shown is a perifollicular inflammatory cell infiltrate with hematoxylin-eosin staining. Original magnification, ×40. (B) Detail of panel A showing hardly recognizable yeast cells in this section in keratinous masses within the infundibular lumen adjacent to the site of wall destruction. Hematoxylin-eosin staining is shown. Original magnification, ×200. (C) Dense perifollicular chronic inflammatory cell infiltrate with amorphous mucinous material in the dilated follicle lumen and PAS stain-positive tiny budding yeasts. PAS staining was used. Original magnification, ×100. (D) Detail of a serial section of the same follicle demonstrating numerous yeast spores within the dilated follicle lumen. PAS staining was used. Original magnification, ×200.

Fig 7

Chemical structures of the currently identified indoles produced by M. furfur when grown on l-tryptophan agar. The corresponding references of the first description of isolation from Malassezia extracts are in parentheses.

Fig 7

Chemical structures of the currently identified indoles produced by M. furfur when grown on l-tryptophan agar. The corresponding references of the first description of isolation from Malassezia extracts are in parentheses.