Researchers now report on a potential new role for some bacteria on the skin: protecting against cancer.

In a study published in Science Advances on February 28, University of California San Diego School of Medicine researchers a type of bacteria commonly found on human skin, Staphylococcus epidermidis produces a substance that may help protect against skin cancer.

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While it is not clear whether the absence of this strain could increase the risk of skin cancer in individuals, the team say that it is possible the findings might one day lead to preventive treatments for patients.

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The finding was somewhat serendipitous. With previous research showing that chemicals produced by Staphylococcus species commonly found on healthy human skin can kill off certain harmful bacteria, the team looked at numerous strains to explore their antimicrobial powers.

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The team discovered the S. epidermidis strain produces the chemical compound 6-N-hydroxyaminopurine (6-HAP). Mice with S. epidermidis on their skin that did not make 6-HAP had many skin tumors after being exposed to cancer-causing ultraviolet rays (UV), but mice with the S. epidermidis strain producing 6-HAP did not.

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6-HAP is a molecule that impairs the creation of DNA, known as DNA synthesis, and prevents the spread of transformed tumor cells as well as the potential to suppress development of UV-induced skin tumors.

Mice that received intravenous injections of 6-HAP every 48 hours over a two-week period experienced no apparent toxic effects, but when transplanted with melanoma cells, their tumor size was suppressed by more than 50 percent compared to controls.

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In the case of S. epidermidis, it appears to also be adding a layer of protection against some forms of cancer, said Gallo. Further studies are needed to understand how 6-HAP is produced, if it can be used for prevention of cancer or if loss of 6-HAP increases cancer risk, said Gallo.

More than 1 million cases of skin cancer are diagnosed in the United States each year. More than 95 percent of these are non-melanoma skin cancer, which is typically caused by overexposure to the sun’s UV rays. Melanoma is the most serious form of skin cancer that starts in the pigment-producing skin cells, called melanocytes.

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This research further adds to a growing understanding of how important the human microbiota, and in this case the skin microbiome, is to health. We have evolved to need these microbes and desperately need to understand all the roles they play in human biology and start to think more about what it is to be a human being,” he said. “The next stage of this exciting work, will be to translate it to human clinical trials and show that this bacterially produced chemical can protect the host from skin cancers.

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