Skin Fungi from Colonization to Infection
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Published on: November 6, 2019
Sybren de Hoog1, Michel Monod2, Tom Dawson3
1Westerdijk Fungal Biodiversity Institute, 3584 CT Utrecht, The Netherlands.
Abstract:
Humans are exceptional among vertebrates in that their living tissue is directly exposed to the outside world. In the absence of protective scales, feathers, or fur, the skin has to be highly effective in defending the organism against the gamut of opportunistic fungi surrounding us. Most (sub)cutaneous infections enter the body by implantation through the skin barrier. On intact skin, two types of fungal expansion are noted: (A) colonization by commensals, i.e., growth enabled by conditions prevailing on the skin surface without degradation of tissue, and (B) infection by superficial pathogens that assimilate epidermal keratin and interact with the cellular immune system. In a response-damage framework, all fungi are potentially able to cause disease, as a balance between their natural predilection and the immune status of the host. For this reason, we will not attribute a fixed ecological term to each species, but rather describe them as growing in a commensal state (A) or in a pathogenic state (B).
Insights
Human skin, unlike other vertebrates, lacks natural protective coverings, making it vulnerable to fungi. Fungi can exist as harmless commensals or harmful pathogens, depending on the host
Area of Science:
- Mycology and Dermatology
- Human-Fungal Interactions
- Immunology
Background:
- Vertebrates exhibit diverse integumentary defenses (scales, feathers, fur) against external threats.
- Humans possess unprotected skin, necessitating robust defense mechanisms against environmental fungi.
- The skin barrier is the primary interface for fungal encounters, leading to colonization or infection.
Purpose of the Study:
- To elucidate the dual nature of fungal interactions with human skin.
- To differentiate between fungal commensalism and pathogenicity on the skin.
- To frame fungal-host interactions within a response-damage paradigm.
Main Methods:
- Observational analysis of fungal growth patterns on intact human skin.
- Categorization of fungal behavior based on tissue interaction.
- Evaluation of host immune status in determining fungal outcomes.
Main Results:
- Two primary modes of fungal expansion on skin: commensal colonization and pathogenic infection.
- Commensal fungi grow without tissue degradation, utilizing surface conditions.
- Pathogenic fungi degrade epidermal keratin and engage the host's cellular immune system.
Conclusions:
- Fungal pathogenicity is contingent upon the host's immune status and the fungus's inherent capabilities.
- A dynamic response-damage balance dictates whether fungi act as commensals or pathogens.
- Fungal species are not inherently commensal or pathogenic but exist in a state relative to the host.
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