Microbial guardians of skin health.
Stacy A, Belkaid Y
Science. 01 2019. doi: 10.1126/science.aat4326
COMMENT: This work describes many beneficial roles that Staphylococcus epidermidis plays in the skin microbiota. These are some of S. epidermidis remarkable functions on skin physiology with important impact on human health:
- S. epidermidis produces antimicrobials and is able to colonize hair follicles
- S. epidermidis produces short-chain fatty acids (SCFAs) that serve to regulate the quantity of microbiota, and, thus, to protect skin integrity.
- SCFAs propionate and valerate inhibit the activity of histone deacetylases (HDACs) in keratinocytes, calibrating the keratinocytes activation status toward either tolerance or inflammation.
- Some S. epidermidis cell wall products are sensed by Toll-like receptors (TLRs) influencing inflammatory responses:
For instance, S. epidermidis TLR2 signaling can limit inflammation after skin injury—an effect that promotes wound healing—as well as during infection with the acne-associated microbe Cutibacterium acnes
- S. epidermidis also interacts with different subsets of T cells:
In early life, cells with regulatory function [for example, regulatory T cells (T regs )] migrate to skin after the skin microbiota colonizes hair follicles. As these T regs are microbiota-specific, they are instrumental to establishing tolerance to skin microbes including S. epidermidis
- In nasal cavity S. epidermidis is able to displace Staphylococcus aureus degrading S. aureus adherence proteins
- In Atopic Dermatitis flares of dry, itchy skin appear to be driven by colonization with S. aureus. It appears to be associated with a loss of S. epidermidis strains that produce S. aureus–targeting bacteriocins.
- A product made by S. epidermidis, the 6-HAP, has anticancer effect:
6-N-hydroxyaminopurine (6-HAP), an antimicrobial that normally targets skin pathogens, has recently been shown to inhibit tumor cell growth. 6-HAP, an analog of the DNA nucleotide base adenine, interferes with the essential process of DNA replication. Keratinocytes, however, are resistant to 6-HAP because, unlike tumor cells, they highly express enzymes that can detoxify 6-HAP. In mice, topical application of 6-HAP–producing strains of S. epidermidis protects against ultraviolet-induced skin tumors
Skin microbes can promote skin immunity, repair, and antimicrobial defense.
S. epidermidis guards skin against inflammation, infections, and cancer through interactions with keratinocytes, T cells, and other members of the skin microbiota. These interactions are strain- and context-dependent, with some leading to negative outcomes for the host, including inflammation and infection.