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MRSA bacteria. Credit: NIH / Tim Sandle

A surgical site infection (SSI) by drug-resistant “super bugs” can double a patient’s mortality rate. Germicidal UV lamps can kill these bacteria, but their broad wavelength spectrum is hazardous to the patient as well as the health care provider. Researchers at the Center for Radiological Research at Columbia University Medical Center (USA) may have found a way to kill drug-resistant bacteria using a narrow wavelength of UV light that doesn’t damage the eyes or skin (PLoS One, doi: 10.1371/journal.pone.0076968). Although in vivo studies are needed to confirm their results, the team members say that 207-nm light may have the potential for safely reducing SSI rates.

Germicidal UV lamps with wavelengths from 200 to 400 nm are commonly used to kill bacteria—including drug-resistant strains like MRSA—but they can also damage biological tissue. The researchers, led by David J. Brenner, found that light in the far-UVC, specifically, 207 nm, can penetrate and kill bacterial cells, but it cannot penetrate through the much larger human cells that make up the skin and outer layer of the eye. (Human cells are about 10 to 25 µm thick, while bacterial cells are typically less than 1 µm in diameter.)

To create the monoenergetic 207-nm beam of light for their experiments, the team used a krypton-bromine excimer lamp with a filter to remove higher-wavelength components. They tested far-UVC-light’s germicidal abilities and safety on MRSA bacterial cells and normal human skin fibroblasts plated on a glass surface. To test far-UVC’s potential to induce pre-mutagentic DNA lesions (damage linked to UV-induced skin cancer), they used a 3-D human skin model.

Their results showed that the far-UVC lamp killed as many plated MRSA bacterial cells as the conventional UV germicidal lamp. However, the far-UVC lamp killed very few human skin cells—quantitatively, they observed 1,000-fold less skin-cell killing with the far-UVC lamp. They also saw nearly zero pre-mutagenic DNA lesions in the 3-D skin models they exposed to far-UVC light, while 3-D skin models subjected to broad-spectrum UV light showed a “high yield” of lesions.

Brenner says that the team’s findings “show that far-UVC light has enormous potential for combating the deadly and costly scourge of drug-resistant surgical site infections.”