With commentary by Patrick Schlievert, Ph.D., professor and department executive officer of microbiology at the University of Iowa Carver College of Medicine
There’s growing evidence that bacteria deep in your digestive system may play a role in the development of type 2 diabetes. Now, recent University of Iowa research suggests something even more surprising: A bug that thrives on the surface of the skin — Staphylococcus aureus (staph) — may also trigger blood-sugar problems.
“We worked with rabbits because their response to staph superantigens is similar to humans’,” says lead researcher Patrick Schlievert, Ph.D., professor and department executive officer of microbiology at the university’s Carver College of Medicine. “We feel we can say it’s a cause of type 2 diabetes in people.” The study was published in the March/April 2015 issue of mBio, the online journal of the American Society for Microbiology.
Schlievert made headlines in the 1980s when his lab at the University of Minnesota identified TSST-1— the staph superantigen responsible for outbreaks of toxic shock syndrome in tampon-users. His work has also shown that super-antigens—poisons churned out by all strains of staph bacteria—disrupt the human immune system and are also responsible for the deadly effects of staph infections of the bloodstream and the heart.
The new study was inspired by a simple observation. “People with diabetes often have higher levels of staph on their skin and dangerously high levels in wounds, such as foot ulcers,” he notes. “This has been attributed to higher blood sugar levels. But we’ve also seen higher levels of staph on the skin of people who are obese. We wanted to find out if staph was a reason obesity increases diabetes risk.”
Schlievert’s team measured the amount of staph and TSST-1 on the skin of four people with diabetes. They then administered comparable amounts to the lab animals. The superantigen stimulated the release of inflammatory compounds called cytokines from fat cells and affected blood sugar. “Small colonies of staph on the skin can produce TSST-1 at levels that won’t cause dramatic symptoms you see in toxic shock syndrome, like fever and low blood pressure. But about 10 percent of the superantigen can penetrate cells,” he says. “We think it’s enough to cause the systemic, chronic inflammation that contributes to insulin resistance and diabetes.”
The researchers are now planning a study that tests the theory in people with pre-diabetes. “They’ll use an investigational body wash that kills staph and we’ll check their blood sugar levels,” he explains. Schlievert also hopes to develop a staph vaccine that could lower risk for type 2 diabetes within five years.
There’s other evidence for a staph-blood sugar connection. A Swedish research group has found a link between staph superantigens and insulin resistance. And in people who already have diabetes, staph infections can make blood sugar levels more difficult to control.
But “the evidence here is too preliminary to make significant conclusions,” says Ignatius W. Fong, M.D., a professor of medicine and infectious-disease specialist at the University of Toronto and author of The Role of Microbes in Common Non-Infectious Diseases (Springer, 2014). “It’s true that about 50 percent of people with diabetes have skin colonization with staph compared to about 25 percent of people without diabetes, but that’s likely because of their diabetes—not the other way around. We need better evidence that skin levels are higher in people who are obese and evidence of superantigens in the blood of people who have staph on their skin.”
Schlievert isn’t perturbed. “It took years for the scientific community to agree that TSST-1 was causing toxic shock syndrome,” he notes. “It took a long time for people to believe that strep, another bacterium, was the cause of flesh-eating disease—which we found in 1987. And it took years for people to believe Barry Marshall, the Australian gastroenterologist who discovered that a bacterium—Helicobacter pylori—was the cause of almost all gastric ulcers. There’s a lot of skepticism in the biomedical community. It can persist for years.”
For now, Schlievert and Fong both say that people, including those with diabetes, shouldn’t take drastic steps to get rid of skin bacteria. “Soap and water is all you need if your skin is healthy and you don’t have any infections,” Fong says.
1. Bao et al: Chronic Superantigen Exposure Induces Systemic Inflammation, Elevated Bloodstream Endotoxin, and Abnormal Glucose Tolerance in Rabbits: Possible Role in Diabetes. March/April 2015 Volume 6 Issue 2 e02554-1; http://mbio.asm.org/content/6/2/e02554-14.full.pdf+html