Fungus on skin
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Fungal Infections on Human Skin: Dermatophytes, Malassezia, and Candida
Dermatophytes and Malassezia: Key Fungal Pathogens
Dermatophytes: Adaptations and Pathogenesis
Dermatophytes are a group of fungi within the Ascomycota phylum that cause a variety of skin diseases. These fungi have evolved to thrive on human skin by encoding multiple enzymes that help them interact with the host. These enzymes include polyketide synthases, nonribosomal peptide synthetases, LysM, proteases, kinases, and pseudokinases, which play roles in modulating host interactions and facilitating infection .
Malassezia: Lipid Dependency and Skin Disorders
Malassezia, a genus within the Basidiomycota phylum, is another significant group of fungi associated with skin conditions such as dandruff, atopic eczema, pityriasis versicolor, seborrheic dermatitis, and folliculitis. These fungi are highly specialized to live on the skin and are dependent on host lipids, secreting lipases and phospholipases to release fatty acids from the host. Malassezia's genome reveals a small size, reflecting its adaptation to the lipid-rich environment of the skin White2014Saunders2012.
Candida: Opportunistic Infections and Risk Factors
Candida Species and Skin Infections
Candida species, particularly Candida albicans, are common commensals in humans but can become pathogenic under certain conditions. These fungi prefer moist environments and can thrive in areas such as the nail folds, cracked skin, and regions contaminated with sugar from glycosuria. Factors such as debility, serious illness, diabetes, antibiotic and steroid therapy, and hypocalcemia can predispose individuals to Candida infections .
Emerging Antifungal Resistance
The rise in the use of immunosuppressive therapies has led to an increase in fungal infections, including those caused by Candida. Antifungal resistance is becoming a significant issue, affecting the treatment success of infections caused by dermatophytes, Candida spp., and Aspergillus fumigatus. Physicians are advised to conduct antifungal susceptibility testing, especially in cases of disseminated infections, to ensure effective treatment .
Immune Response and Inflammation
Malassezia and the IL-17 Response
Malassezia fungi can trigger a type 17 immune response, which is crucial for preventing fungal overgrowth on the skin. This response involves the production of IL-17 and related cytokines. However, in conditions of impaired skin integrity, such as atopic dermatitis, the presence of Malassezia can exacerbate inflammation, highlighting the dual role of the immune response in both protecting against and promoting skin inflammation .
Fungal Diversity and Skin Microbiome
Fungal Communities on Human Skin
The human skin hosts a diverse range of fungal communities, with Malassezia species dominating most body sites. However, areas such as the feet exhibit greater fungal diversity. The skin's physiological attributes and topography significantly influence the composition of these microbial communities. Understanding these interactions is essential for comprehending how pathogenic and commensal fungi contribute to skin health and disease .
Age-Related Changes in Skin Fungal Communities
Fungal communities on the skin change with age. In children, the skin is colonized by a more diverse range of fungi, including Eurotiomycetes, which are common dermatophytes. In contrast, adult skin is predominantly colonized by lipophilic Malassezia species. These shifts are likely due to changes in sebaceous gland activity and sebum composition during puberty .
Conclusion
Fungal infections on the skin are caused by a variety of pathogens, including dermatophytes, Malassezia, and Candida. These fungi have evolved unique mechanisms to thrive on the skin, and their interactions with the host can lead to various skin disorders. The rise in antifungal resistance and the role of the immune response in fungal infections underscore the need for continued research and effective treatment strategies. Understanding the diversity and dynamics of skin fungal communities is crucial for developing targeted therapies and improving patient outcomes.
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