A narrow spectrum of ultraviolet light can destroy drug-resistant bacteria but is safe for human exposure, a new study says, and may be a way to reduce the serious and stubborn problem of surgical wound infections. It’s been known for years that UV light is effective at killing bacteria, and standard germicidal lamps that emit wavelengths from about 200 to 400 nm are used routinely to decontaminate surgical equipment. “Unfortunately, this UV light is also harmful to human tissue and can lead to skin cancer and cataracts in the eye,” said Columbia University Medical Center study leader David J. Brenner, Ph.D. “UV light is almost never used in the operating room during surgery, as these health hazards necessitate the use of cumbersome protective equipment for both surgical staff and patients.” Although 207-nm UV light can penetrate and kill bacteria such as MRSA, it is unable to penetrate to the nucleus of human cells. UV from conventional lamps can penetrate and damage human cells. Right panel: Unlike UV from conventional lamps, 207-nm UV light is unable to penetrate the surface layer of dead skin to reach sensitive cells in the epidermis. Images courtesy of Dr. David Brenner, Columbia University Medical Center. Conducting studies in tissue culture, his team found that narrow-spectrum UV light of 207 nm dramatically reduces surgical wound infections without damaging tissue. Such infections affect as many as 300,000 patients a year and kill up to 8200 in the US alone. Patients with surgical wound infections, compared with those without such infections, are also 60 percent more likely to spend time in an ICU, are five times as likely to be readmitted to the hospital, have twice the mortality rate, have longer hospital stays, and have roughly double the total health care costs. The 207-nm light is strongly absorbed by proteins but can't reach the nucleus of human cells at the cellular level, and cannot reach the sensitive cells in the epidermis and eye at the tissue level. “What this means is, if you shone 207-nm light on human skin or eyes, you would not expect to see any biological damage,” Brenner said, “but it should kill any airborne bacteria that land on a surgical wound.” To test their hypothesis, Brenner and colleagues exposed MRSA (methicillin-resistant S. aureus) bacteria, a common cause of surgical wound infections, and human skin cells to a krypton-bromine (KrBr) excimer lamp that emits UV light only at 207 nm; they also exposed the bacteria to a standard germicidal UV lamp. They found that 207-nm UV light was as effective at killing MRSA bacteria as a conventional UV lamp, but killed one-thousandfold fewer human skin cells than did the standard UV light. In another experiment, the researchers tested the two UV lamps on a standard tissue-culture model of human skin (which includes the major skin layers, the epidermis and dermis). Exposure to a standard UV lamp caused extensive precancerous changes in the epidermis, while exposure to the same level of 207-nm light did not. An excimer lamp shining 207-nm UV light on MRSA bacteria in a petri dish. “Our results to date suggest that 207-nm UV light may be an effective add-on to current infection-control measures, without the need for protective equipment for staff or patients,” Brenner said. “We need all the tools we can get to reduce surgical wound infections, especially those involving drug-resistant strains of bacteria, which have become increasingly common.” A main route to surgical infection is through the air, he said. “Despite every possible effort to promote sterility, MRSA and other bacteria are essentially raining down on the wound during the entire surgery,” he said. “If this UV lamp were continuously shone on the wound during surgery, the bacteria would be killed as they landed.” The researchers are now conducting in vivo tests of the 207-nm excimer lamp, which is small, rugged, inexpensive and long-lived. The paper, “207-nm UV Light — A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. I: In Vitro Studies,” appears in PLOS ONE. For more information, visit: cumc.columbia.edu or columbiadoctors.org