The new research was carried out by scientists at the University of California (UC) San Diego School of Medicine.
Dr. Richard Gallo, Ph.D., chair of the Department of Dermatology at UC San Diego, is the new study's corresponding author.
He and his colleagues performed a molecular analysis of the bacteria's metabolic products found on human skin and discovered that strains of the so-called Staphylococcus epidermidis produce a chemical that protects against the formation and development of skin cancer.
According to the American Academy of Dermatology, more than 1 million U.S. citizens live with skin cancer, and 1 in 5 will develop the condition at one point in their lives.
The Centers for Disease Control and Prevention (CDC) caution against the risks of sun exposure and intentional tanning, as the sun's ultraviolet (UV) rays are known to raise skin cancer risk.
In the new study, Dr. Gallo and team used cancer-inducing UV rays in mice with S. epidermidis.
Tumor size halved
The researchers found that S. epidermidis produces a chemical called 6-N-hydroxyaminopurine (6-HAP), which is a molecule that inhibits DNA synthesis. By doing so, 6-HAP has the potential to stop transformed tumor cells from spreading.
Using a mouse model, the researchers compared the effect of carcinogenic UV rays in two groups of mice, comprising: rodents in which S. epidermidis produced 6-HAP, or rodents in which the bacterium did not produce the beneficial compound.
Dr. Gallo and his team administered 6-HAP shots to one group of mice once every 48 hours for 2 weeks. Additionally, they transplanted melanoma cells in these rodents.
Compared with the control group of mice — that did not receive 6-HAP — the intervention mice had a 50 percent reduction in tumor size. Importantly, the intervention mice experienced no toxic side effects.
Dr. Gallo sums up the findings, saying:
"We have identified a strain of S. epidermidis, common on healthy human skin, that exerts a selective ability to inhibit the growth of some cancers."
"This unique strain of skin bacteria produces a chemical that kills several types of cancer cells but does not appear to be toxic to normal cells," he continues.
But Dr. Gallo also says that more studies are necessary to fully grasp how 6-HAP is produced, and to determine whether a decrease in the chemical raises skin cancer risk in humans or having the chemical confers a preventative effect.
"S. epidermidis strains producing 6-HAP," add the authors, "were found in the metagenome from multiple healthy human subjects, suggesting that the microbiome of some individuals may confer protection against skin cancer."
"There is increasing evidence that the skin microbiome is an important element of human health. In fact," Dr. Gallo says, "we previously reported that some bacteria on our skin produce antimicrobial peptides that defend against pathogenic bacteria such as Staph aureus."