Published On Feb 04, 2016
Blue Light Special
Drug-resistant bugs have spurred research into a promising—and surprisingly simple—treatment.
Victims of traumatic injuries and severe burns mostly die from complications of infection. When the skin has been badly damaged, it leaves an easy opening for invading pathogens. Those harmful microbes, unchecked, can trigger sepsis, a full-body inflammatory response that is often fatal. The culprits most often at fault are drug-resistant strains of microbes that lurk in hospitals and resist easy treatment.
One new idea for eradicating them literally sheds light on the problem. The blue spectrum of light, it turns out, kills some of the most intractable microbial invaders. This blue light can be administered easily on open wounds. And the bacteria killed in this way don’t seem to develop resistance to the treatment—a fact that might open up a new front on the war against drug-resistant bugs.
Tianhong Dai, an assistant biomedical engineer at the Wellman Center for Photomedicine at Massachusetts General Hospital (MGH), focused his team’s blue light research on exploring challenges posed by the U.S. Department of Defense. Mice with third-degree burns were infected with a strain of Acinetobacter baumannii, a common drug-resistant bacterium. (The strain was taken from a soldier in Iraq to test possible applications on the battlefield.) After a single hour of blue light treatment, A. baumannii was no longer detected and the infection did not recur.
Moreover, the pathogens seemed to remain susceptible to blue light even after repeated exposures. “We actually carried out a later study to see if we could artificially induce blue light resistance,” says Dai. “But we failed.” In fact, Acinetobacter became even more susceptible to blue light with increased exposures, he says.
Treating infections with light, as revolutionary as it may sound, is far from a new idea. In 1903, Niels Ryberg Finsen of Denmark received the Nobel Prize for his work with light therapy as a treatment for lupus vulgaris, a form of tuberculosis that causes lesions on the skin. He developed an ultraviolet device called the Finsen lamp and documented its bactericidal effects. Yet while hospitals still use ultraviolet light as a disinfectant, light research mostly took a backseat after the discovery of antibiotics. Now the field has seen a flood of new interest in an era when antibiotics are showing vulnerability—their effectiveness gradually decreasing as bacteria slowly become resistant.
Some aspects of how light kills these bacteria are now understood, says Dai. Some microbes naturally contain chromophores, or molecules that absorb certain wavelengths of light. When both oxygen and blue-violet light are present, the chromophores produce molecules that are highly unstable, known as oxygen radicals or reactive oxygen species. These damage cell membranes, which may be what kills the bacteria.
But why blue? Ultraviolet light can be harmful to the skin and eyes. Red light from lasers and LEDs has shown promise in killing pathogens and cancer cells, but it doesn’t trigger the photochemical process without special dyes that act as photosensitizers. In contrast, “blue light kills bacteria without photosensitizers,” says Dai. “It’s simple and inexpensive.”
Blue light holds promise for controlling other infections as well. Michael Hamblin, principal investigator at the Wellman Center, showed that blue light delivered through an endoscope could potentially eradicate Helicobacter pylori in the stomach, a cause of ulcers and stomach cancer. Other studies have demonstrated blue light’s antimicrobial effect on other troublesome bugs, including Clostridium difficile and Candida albicans.
Still, the technology presents some challenges. Blue light doesn’t penetrate deep into tissue, which may limit its use beyond disinfecting skin or wounds. And it will need to show that its effects are lasting. When a startup company tried to develop Hamblin’s finding into a commercially viable endoscopic light device to treat peptic ulcers, H. pylori repopulated within days.
Dai and his colleagues are still establishing the basic science of blue light, and clinical trials with human trauma and burn patients are still to come. But with 2 million illnesses and about 23,000 deaths attributed to antibiotic resistance each year, public health authorities are anxious to find novel ways to kill pathogens.
David Hooper, associate chief of the Division of Infectious Diseases at MGH, who consults on burn patients’ progress with sepsis, says he is “cautiously optimistic” that blue light will emerge as a new way to fight or prevent infection, especially for burn victims. “Sometimes what seems like an unexpected, interesting idea really does work out,” he says.