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

Abstract

We have previously shown that 207-nm ultraviolet (UV) light has similar antimicrobial properties as typical germicidal UV light (254 nm), but without inducing mammalian skin damage. The biophysical rationale is based on the limited penetration distance of 207-nm light in biological samples (e.g. stratum corneum) compared with that of 254-nm light. Here we extended our previous studies to 222-nm light and tested the hypothesis that there exists a narrow wavelength window in the far-UVC region, from around 200–222 nm, which is significantly harmful to bacteria, but without damaging cells in tissues. We used a krypton-chlorine (Kr-Cl) excimer lamp that produces 222-nm UV light with a bandpass filter to remove the lower- and higher-wavelength components. Relative to respective controls, we measured: 1. in vitro killing of methicillin-resistant Staphylococcus aureus (MRSA) as a function of UV fluence; 2. yields of the main UV-associated premutagenic DNA lesions (cyclobutane pyrimidine dimers and 6-4 photoproducts) in a 3D human skin tissue model in vitro; 3. eight cellular and molecular skin damage endpoints in exposed hairless mice in vivo. Comparisons were made with results from a conventional 254-nm UV germicidal lamp used as positive control. We found that 222-nm light kills MRSA efficiently but, unlike conventional germicidal UV lamps (254 nm), it produces almost no premutagenic UV-associated DNA lesions in a 3D human skin model and it is not cytotoxic to exposed mammalian skin. As predicted by biophysical considerations and in agreement with our previous findings, far-UVC light in the range of 200–222 nm kills bacteria efficiently regardless of their drug-resistant proficiency, but without the skin damaging effects associated with conventional germicidal UV exposure.

Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases

“…For comparison, using a similar experimental arrangement, but using a conventional 254 nm germicidal UVC lamp, McDevitt et al 19 found a D95 value of 1.1 mJ/cm 2 (95% CI: 1.0–1.2) for H1N1 virus. Thus as we 13,15 and others 16–18 reported in earlier studies for bacterial inactivation, 222-nm far-UVC light and 254-nm broad-spectrum germicidal light are quite similar in their efficiencies for viral inactivation, the comparatively small differences presumably reflecting differences in nucleic acid absorbance. However as discussed above, based on biophysical considerations and in contrast to the known human health safety issues associated with conventional germicidal 254-nm broad-spectrum UVC light, far-UVC light does not appear to be cytotoxic to exposed human cells and tissues in vitro or in vivo 13–15 .…”

“…We have developed an approach to UV-based sterilization using single-wavelength far-UVC light generated by filtered excilamps, which selectively inactivate microorganisms, but does not produce biological damage to exposed mammalian cells and tissues 13–15 . The approach is based on biophysical principles in that far-UVC light can traverse and therefore kill bacteria and viruses which are typically micrometer dimensions or smaller, whereas due to its strong absorbance in biological materials, far-UVC light cannot penetrate even the outer dead-cell layers of human skin, nor the outer tear layer on the surface of the eye.…”

“…We used a bank of three excimer lamps containing a Kr-Cl gas mixture that predominantly emits at 222 nm 26,27 . The exit window of each lamp was covered with a custom bandpass filter designed to remove all but the dominant emission wavelength as previously described 15 . Each bandpass filter (Omega Optical, Brattleboro, VT) had a center wavelength of 222 nm and a full width at half maximum (FWHM) of 25 nm and enables >20% transmission at 222 nm.…”

“…By contrast, we have earlier shown that far-UVC light generated by filtered excimer lamps emitting in the 207 to 222 nm wavelength range, efficiently kills drug-resistant bacteria, without apparent harm to exposed mammalian skin 13–15 . The biophysical reason is that, due to its strong absorbance in biological materials, far-UVC light does not have sufficient range to penetrate through even the outer layer (stratum corneum) on the surface of human skin, nor the outer tear layer on the outer surface of the eye, neither of which contain living cells; however, because bacteria and viruses are typically of micron or smaller dimensions, far-UVC light can still efficiently traverse and inactivate them 13–15 .…”

Efficient Microbial Decontamination of Translucent Liquids and Gases Using Optical Metamaterials

“…UV-C radiation is effective for inactivating protozoa, bacteria, viruses, and many microorganisms. According to literature [17][18][19][20][21], the use of UV-C radiation is especially a good, environment-friendly, and chemical-free method to inactivate dangerous pathogens in diverse condition. UV-C cannot pass through our atmosphere, so it does not contribute to DNA damage.…”