Bacteria seem to love company, and for good reason. When bacteria get together in sufficient numbers, they can then signal to each other and throw up a protective layer of slime—a biofilm—to hide behind.
For decades, scientists have known that bacteria form these slimy fortresses everywhere from the grout in your shower to the inside of oil pipelines. Feel around a bit with your tongue and you may be able to find a sample in your very own mouth: The most familiar form of biofilm is dental plaque, the stuff you should be brushing off your teeth every day.
Yet scientists have only recently realized that biofilms also play a major role in infections. Doctors are familiar with the typical symptoms: Patients show up with fevers and elevated white blood cell counts, classic indications that the body is trying to fight off an infection. Antibiotics are prescribed. The symptoms go away—and then come back as soon as the course of drugs is over.
Kendra Rumbaugh, PhD, a biologist at Texas Tech University Health Sciences Center in Lubbock, Texas, thinks she knows why. Somewhere, a colony of bacteria hiding under a biofilm has bounced back. Once bacteria get inside a cut or sore and start putting up those barriers—a process that can happen in a matter of hours—they’re tough to get out. “Most bacteria don’t want to float around in the environment,” Rumbaugh says. But with biofilms, “they’re enclosed in this shell, and that makes the bacteria very resistant to antibiotics.” Attacking from behind their biofilm wall, bacteria can keep an infection raging indefinitely. It takes 100 to 1,000 times as much antibiotic to kill bacteria protected by biofilms as it does to kill bacteria floating around on their own. “The dose required to kill biofilm would have severe effects on our cells too,” Rumbaugh explains.
Assistant Professor Texas Tech University Health Sciences Center
ADA Research Grant
For people with diabetes, biofilms can be especially dangerous. “One of the reasons [diabetic] wounds are so hard to heal is that the diabetic wound environment contributes to the formation of biofilms,” Rumbaugh says. Specifically, the circulation problems and nerve damage that can occur with diabetes make wounds particularly prone to infection and can foster biofilms. Nowhere is the problem more serious than in foot ulcers. An estimated 25 percent of people with diabetes will develop serious wounds on their feet at some point, and chronic infections mean a quarter of those will require amputation. Some doctors consider diabetic foot ulcers the most common chronic wound in the world. Treating them cost tens of billions of dollars last year in the United States alone.
So far, the standard approach has been to simply remove the infected area, whether it’s a tooth pitted with cavities or a foot festering with infection. But the so-called “orthopedic solution”—one medical euphemism for amputating an infected foot or leg—can have devastating consequences for a person’s quality of life. For many, amputation is the beginning of the end. The statistics are scary: Half of diabetic amputees die within 18 months of their operation, and 80 percent won’t survive five years.
Last year Rumbaugh, one of the country’s leading experts on biofilms and infection, published the first evidence that bacteria in burn wounds form biofilms. With a grant from the American Diabetes Association, Rumbaugh is now turning her attention to diabetic wounds. Experimenting on diabetic mice, she studies the biofilms that develop in infected wounds under the microscope to see how and why they thrive.
Rumbaugh’s research is helping doctors find a way to battle biofilms without amputations. One breakthrough was her discovery that bacteria cluster around blood vessels, where nutrients are plentiful and their biofilms protect them from the body’s white blood cells and other defenses. She also found that bacteria penetrate deeper into the flesh than previously thought, sometimes as deep as 5 millimeters, or 0.2 inches.
The information coming out of her lab helps doctors develop new strategies to treat diabetic patients with infected ulcers and wounds. “Now I know what I’m dealing with,” says Randall Wolcott, who runs a private wound care clinic in Lubbock called the Medical Biofilm Research Institute. “I credit her for a quantum leap in treating this.”
Thanks to Rumbaugh’s research, Wolcott changed the way he treated foot ulcers, using chemicals designed to disrupt the formation of biofilms and removing flesh that might harbor bacteria without removing the entire foot. The results—published in the Journal of Wound Care in April—were remarkable. “Eighty percent of the wounds are healing,” Rumbaugh says. “That’s a lot of limbs being saved.”