A Tiny Bit Of UV Light May Prevent 8,000 Surgical Deaths Per Year

Columbia scientists figure out a way to destroy drug resistant bacteria with UV light without harming regular tissue.

By Nsikan Akpan on October 16, 2013 5:00 PM EDT

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Surgery is hard enough without drug-resistant bacteria mucking up the works. Researchers at Columbia University have devised a straightforward solution for this health risk that causes up to 300,000 life-threatening, post-op infections each year: zap the buggers with ultraviolet (UV) light.

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Wait...aren't UV light rays hazardous too? What gives? It is true that UV light triggers DNA mutations that spawn skin cancer, explaining why we wear sunscreen during the summer when these rays are most intense. 

But physicians have long wondered if UV lamps, which have been used for decades to sterilize surgical equipment, could be applied for eliminating bacteria from wounds during surgery. If they were successful, the procedure could reduce the threat of "super germs", such as MRSA (methicillin-resistant S. aureus) bacteria. 

"Unfortunately, [standard] UV light is also harmful to human tissue and can lead to skin cancer and cataracts in the eye," said study leader Dr. David Brenner, the Higgins Professor of Radiation Biophysics and director of the Center for Radiological Research at the Columbia University Medical Center. "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."

The trick for Brenner's team was finding a level of UV exposure that destroy bacteria but do not harm human tissue. They settled on a krypton-bromine excimer lamp, which emits a very narrow spectrum of UV light at 207 nanometers.

"A 207 nanometer lamp was chosen because UV light at its wavelength is very strongly absorbed by biological materials (proteins in particular), so the UV light has very limited ability to penetrate either individual human cells, or the dead-cell layer at the surface of our skin," Brenner told Medical Daily. "So we expected it to be safe from the perspective of human exposure." 

Left panel: 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.  Credit: Dr. David Brenner, Columbia University Medical Center
Left panel: 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. Credit: Dr. David Brenner, Columbia University Medical Center

To explore this hunch, the researchers exposed human skin tissue growing in a dish - mimicking the two major layers of skin: the epidermis and dermis - to light from an excimer lamp.

The excimer lamp was a 1000-fold less harmful to human tissue than a standard UV lamp. In contrast, the excimer rays were just as potent at destroying MRSA bacteria as a regular UV lamp.

The key difference is the size of our cells, according to the researchers. Human cells are larger, so the UV rays have to travel a longer distance to reach the nucleus, which houses our DNA. 

They reason that UV rays from the excimer lamp is too weak to penetrate a human nucleus, but are still powerful enough to seep through bacteria, which are 10 times smaller than animal cells.  

In accordance with this theory, the excimer lamp caused zero DNA lesion in humans, whereas standard UV led to abundant mutations.

Excimer lamps are small and inexpensive, the researchers wrote, so they could be the ideal solution for surgical infections that cause 8,200 deaths per year and between $3-10 billion in healthcare expeditures. Patient suffering from surgical infections are 60 percent more likely to require intensive care and have double the mortality rate of those who don't catch 'a bug' during surgery.

"Despite every possible effort to promote sterility, MRSA and other bacteria are essentially raining down on the wound during the entire surgery," Brenner said. "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. If this UV lamp were continuously shone on the wound during surgery, the bacteria would be killed as they landed." 

Source: Buonanno M, Randers-Pehrson G, Bigelow AW, et al. 207-nm UV Light - A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. I: In-Vitro Studies. PLoS One. 2013.

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