207-nm UV Light—A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. II: In-Vivo Safety Studies

Abstract

BackgroundUVC light generated by conventional germicidal lamps is a well-established anti-microbial modality, effective against both bacteria and viruses. However, it is a human health hazard, being both carcinogenic and cataractogenic. Earlier studies showed that single-wavelength far-UVC light (207 nm) generated by excimer lamps kills bacteria without apparent harm to human skin tissue in vitro. The biophysical explanation is that, due to its extremely short range in biological material, 207 nm UV light cannot penetrate the human stratum corneum (the outer dead-cell skin layer, thickness 5–20 μm) nor even the cytoplasm of individual human cells. By contrast, 207 nm UV light can penetrate bacteria and viruses because these cells are physically much smaller.AimsTo test the biophysically-based hypothesis that 207 nm UV light is not cytotoxic to exposed mammalian skin in vivo.MethodsHairless mice were exposed to a bactericidal UV fluence of 157 mJ/cm2 delivered by a filtered Kr-Br excimer lamp producing monoenergetic 207-nm UV light, or delivered by a conventional 254-nm UV germicidal lamp. Sham irradiations constituted the negative control. Eight relevant cellular and molecular damage endpoints including epidermal hyperplasia, pre-mutagenic UV-associated DNA lesions, skin inflammation, and normal cell proliferation and differentiation were evaluated in mice dorsal skin harvested 48 h after UV exposure.ResultsWhile conventional germicidal UV (254 nm) exposure produced significant effects for all the studied skin damage endpoints, the same fluence of 207 nm UV light produced results that were not statistically distinguishable from the zero exposure controls.ConclusionsAs predicted by biophysical considerations and in agreement with earlier in vitro studies, 207-nm light does not appear to be significantly cytotoxic to mouse skin. These results suggest that excimer-based far-UVC light could potentially be used for its anti-microbial properties, but without the associated hazards to skin of conventional germicidal UV lamps.

Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light

“…In agreement with our previous results using 207-nm light (7,8), here we showed that 222-nm light has similar antimicrobial properties as a conventional germicidal lamp but without causing mammalian skin damage.…”

“…One group of three mice was exposed to fluence of 157 mJ/cm 2 from 222 nm light delivered in a 7 h period by a filtered Kr-Cl excimer lamp while another group of three mice was sham irradiated to zero UV fluence. Mice exposed to 157 mJ/cm 2 delivered in 7 h period from 254 nm light represented the positive controls (8).…”

“…We have previously shown that 207-nm light emitted by a filtered krypton-bromine (Kr-Br) excilamp has bactericidal efficacy while being minimally cytotoxic to human cells in a 3D skin tissue model in vitro (7) and in a hairless mouse skin model in vivo (8). Thus, continuous exposure of the wound to far-UVC light during surgery may inactivate the microbes alighting directly onto the surgical wound from the air.…”

“…We further tested eight cellular and molecular endpoints relevant to skin damage in vivo in dorsal skin of hairless mice 48 h after exposure to 222-nm or 254-nm light used as positive control (8), at a fluence at which the 254-nm light is predicted to produce a significant decrease in SSI rates (22).…”

2019 Novel Coronavirus (COVID-19) Pandemic: Built Environment Considerations To Reduce Transmission

“…More recently, far-UVC light in the 207-to 222-nm range has been demonstrated to effectively inactivate airborne aerosolized viruses. While preliminary findings from in vivo rodent models and in vitro three-dimensional (3-D) human skin models appear favorable to not cause damage to human skin and eyes (90,91), further research must be conducted to verify the margin of safety before implementation. If implemented safely, UVC and UVGI light offers a range of potential disinfectant strategies for buildings and is a common strategy for deep clean practices in health care settings.…”