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207 nm UV kills MRSA, safe for skin tissue in vivo

MRSA bacteria - photo courtesy NIH/Tim Sandle, PhD

MRSA bacteria - photo courtesy NIH/Tim Sandle, PhD

In vivo trials have shown that far-band, 207 nm ultraviolet (UV)-C light is as effective at killing methicillin-resistant Staphylococcus aureus (MRSA) in wounds as conventional antibacterial UV light while at the same time not harming the surrounding skin tissue.

The findings were published online ahead of print in PLOS One (June 8, 2016).

“Our new findings show that far-UVC light has enormous potential for combating the deadly and costly scourge of drug-resistant surgical site infections,” the paper’s lead author, David J. Brenner, PhD, Higgins Professor of Radiation Biophysics, director of the Center for Radiological Research at the Columbia University Medical Center in New York, said in a press release.

Wavelength too short to damage skin cells

In the paper, the authors note that the hypothesis regarding why this wavelength of UV can kill bacteria but not healthy cells is that the extremely short wavelength is unable to penetrate the stratum corneum, or even the cytoplasm of individual cells, but is able to penetrate bacteria, which are physically much smaller.

Earlier in vitro studies from the same research team showed no harm to human tissue, which prompted this animal-model study in hairless mice.

Head-to-head comparison with conventional 254 nm UV

In the trial, the mice were exposed to a bactericidal UV fluence of 157 mJ/cm2 either delivered by a filtered Kr-Br excimer lamp producing monoenergetic 207-nm UV light, or by a conventional 254-nm UV germicidal lamp. Sham irradiations were used as a negative control. Epidermal hyperplasia, pre-mutagenic UV-associated DNA lesions, skin inflammation, and normal cell proliferation and differentiation in skin harvested 48 hours after exposure were the evaluated end points.

The conventional germicidal 254 nm UV exposure produced significant effects for all the studied skin damage endpoints, while the 207 nm device, at the same fluence, produced results not statistically distinguishable from the controls.

“We’ve known for a long time that UV light has the potential to reduce surgical site infections, because UV can efficiently kill all bacteria, including drug-resistant bacteria and even so-called ‘superbugs.’ Unfortunately, it’s not possible to use conventional germicidal UV light when people are around because it’s a health hazard to patients and medical personnel. What we showed in our earlier work is that far-UVC light is as effective at killing MRSA as conventional germicidal UV light—and now with this new research, we have demonstrated that far-UVC kills bacteria but without risk of skin damage,” Dr. Brenner said.

Potential applications

Dr. Brenner said the findings suggest 207 nm UVC may be a practical approach to reducing surgical site infection rates without risking the health and safety of either patients or medical professionals.

The team plans to conduct direct studies of the UVC irradiation in surgical settings in both larger animals and in humans, as well as to explore alternative uses including killing airborne bacteria and viruses.

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