Meet the bacteria living on your skin: S. epidermidis

Bacteria have adapted to survive in the harshest of environments; from the crushing pressure and violent heat of hydrothermal vents, to radioactive levels thousands of times higher than what any other organism could survive. With the extremes being such fascinating cases to observe, it is easy for those closest to us to go unnoticed. Many people associate bacteria with disease, so the positive effects of bacteria on skin health are less commonly discussed. However, one species of bacteria in particular, Staphylococcus epidermidis, has been the focus of recent scientific investigation for its unique role in maintaining skin hydration.

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Living on the skin

How does a bacterium survive on human skin? S. epidermidis utilizes an enzyme called sphingomyelinase, whose function is to accelerate the breakdown rate of a lipid found on cell surfaces. This reaction produces both ceramides and phosphocholine, the latter of which is a nutrient source for the bacteria and also helps them survive in the high salinity environment. The ceramides produced as a by-product are precisely what aid in maintaining skin hydration. In a mouse-model study, the skin of mice were exposed to common irritants such as detergent, then treated with S. epidermidis. In comparison to mice whose skin were not treated with the bacteria, the treated mice experienced reduced water loss and increased ceramide content. When this was repeated on mice who did not undergo exposure to common skin irritants but had depleted levels of ceramides, reduced water loss was experienced once again.

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Even more benefits

A strengthened ceramide barrier is not the only way in which S. epidermidis synergizes with your skin. It has also been found to produce compounds that work with antimicrobial peptides produced by keratinocytes to eradicate harmful bacteria. Furthermore, they produce another compound that can dampen inflammatory responses from injury, effectively accelerating wound healing. Third, and which is the basis of the research presented in the following paragraph, is that the early colonization is essential for developing certain immune cells, and will also aid the immune system in distinguishing between commensal and pathogenic bacteria long-term.

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A living vaccine

In another mouse-model study, researchers wanted to determine if S. epidermidis could be used to train the immune system to recognize cancer cells since it can prime the immune system without causing infections or inflammation. S. epidermidis was modified to display tumor-related proteins on its surface, then placed on the skin of mice. They successfully trained the mice’s immune system to make T-cells that specifically targeted tumor proteins. These T-cells both slowed tumor growth and caused tumor shrinkage. This approach didn’t cause any harmful inflammation, and the mice retained T-cells trained to recognize the tumor, suggesting lasting immunity. This research suggests that S. epidermidis could potentially be used as a vaccine and train the immune system to recognize and fight against cancer cells.

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Some negative effects

It is worth mentioning that there is some correlation between certain strains of S. epidermidis and the exacerbation of certain skin conditions such as eczema. Studies suggest that this may be associated with the occlusion of sweat glands and the production of a separate enzyme.

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Final thoughts

While S. epidermidis may not be able to survive in extreme conditions, it has established a successful habitat on the human skin. It plays a role in maintaining skin hydration through the production of ceramides, synergizes with your skin to produce antimicrobial peptides that eradicate harmful bacteria, dampens inflammatory responses from injury to accelerate wound healing, and is able to prime the immune system with the potential to develop living vaccines targeted to cancer cells. From creams to vaccines, S. epidermidis opens a multitude of avenues for future skin treatments.

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References

Brown, M. M., & Horswill, A. R. (2020). Staphylococcus epidermidis-Skin friend or 

foe?. PLoS pathogens, 16(11), e1009026. https://doi.org/10.1371/journal.ppat.1009026

Zheng, Y., Hunt, R. L., Villaruz, A. E., Fisher, E. L., Liu, R., Liu, Q., Cheung, G. Y. C., Li, M., & Otto, M. (2022). Commensal Staphylococcus epidermidis contributes to skin barrier homeostasis by generating protective ceramides. Cell Host & Microbe, 30(3), 301-313.e9. https://doi.org/10.1016/j.chom.2022.01.004

Chen, Y. E., Bousbaine, D., Veinbachs, A., Atabakhsh, K., Dimas, A., Yu, V. K., Zhao, 

A., Enright, N. J., Nagashima, K., Belkaid, Y., & Fischbach, M. A. (2023). Engineered skin bacteria induce antitumor T cell responses against melanoma. Science (New York, N.Y.), 380(6641), 203–210. https://doi.org/10.1126/science.abp9563