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

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.

我们先前已表明，207纳米紫外线（UV）具有与典型的杀菌紫外线（254纳米）相似的抗菌特性，但不会引起哺乳动物皮肤损伤。其生物物理原理基于207纳米光在生物样本（例如角质层）中的穿透距离比254纳米光有限。在此，我们将先前的研究扩展到222纳米光，并验证了一个假设：在远紫外线C（far - UVC）区域存在一个狭窄的波长窗口，大约在200 - 222纳米之间，它对细菌有显著危害，但不会损伤组织中的细胞。我们使用了一个氪氯（Kr - Cl）准分子灯，它产生222纳米的紫外线，并配有带通滤波器以去除较低和较高波长的成分。相对于各自的对照，我们测量了：1. 耐甲氧西林金黄色葡萄球菌（MRSA）在体外随紫外线通量的杀灭情况；2. 在体外三维人体皮肤组织模型中主要的与紫外线相关的致突变前DNA损伤（环丁烷嘧啶二聚体和6 - 4光产物）的产生量；3. 在体内暴露的无毛小鼠中八个细胞和分子皮肤损伤指标。我们将其与用作阳性对照的传统254纳米紫外线杀菌灯的结果进行了比较。我们发现222纳米光可有效杀灭MRSA，但与传统的杀菌紫外线灯（254纳米）不同，它在三维人体皮肤模型中几乎不产生与紫外线相关的致突变前DNA损伤，并且对暴露的哺乳动物皮肤没有细胞毒性。正如生物物理方面的考虑所预测的，并与我们先前的发现一致，200 - 222纳米范围内的远紫外线C光可有效杀灭细菌，无论其耐药程度如何，但没有与传统杀菌紫外线暴露相关的皮肤损伤效应。