Department of Food Science, Cornell University, Ithaca, NY, 14850, USA.
Universidad Autónoma de Querétaro, Santiago de Querétaro, Mexico.
Sci Rep. 2020 Feb 25;10(1):3411. doi: 10.1038/s41598-020-60459-8.
Irradiation with deep-ultraviolet light-emitting diodes (DUV LEDs) is emerging as a low energy, chemical-free approach to mitigate microbial contamination, but the effect of surface conditions on treatment effectiveness is not well understood. Here, inactivation of L. innocua and E. coli ATCC25922, as examples of Gram-positive and Gram-negative bacteria, respectively, by DUV LED of 280 nm wavelength was studied. Surface scenarios commonly encountered in environmental, clinical or food processing environments were used: nutrient rich surfaces, thin liquid films (TLF), and stainless steel surfaces (SS). DUV LED exposure achieved 5-log reduction for both strains within 10 min in most scenarios, except for TLF thicker than 0.6 mm. Inactivation kinetics in TLF and on dry SS followed the Weibull model (0.96 ≤ R ≤ 0.99), but the model overestimated inactivation by small-dose DUV on wet SS. Confocal microscopy revealed in situ that bacteria formed a dense outer layer at the liquid-air interface of the liquid droplet, protecting the cells inside the droplet from the bactericidal DUV. This resulted in lower than anticipated inactivation on wet SS at small DUV doses, and deviation from the Weibull model. These findings can be used to design effective DUV LED disinfection strategies for various surface conditions and applications.
深紫外发光二极管（DUV LEDs）照射作为一种低能量、无化学物质的方法，正在被用来减轻微生物污染，但表面条件对处理效果的影响还不是很清楚。在这里，以革兰氏阳性菌 L. innocua 和革兰氏阴性菌 E. coli ATCC25922 为例，研究了波长为 280nm 的 DUV LED 对它们的灭活效果。使用了在环境、临床或食品加工环境中常见的表面情况：营养丰富的表面、薄液膜（TLF）和不锈钢表面（SS）。在大多数情况下，除了 TLF 厚度大于 0.6mm 之外，DUV LED 照射在 10 分钟内就可以使两种菌株的数量减少 5 个对数级。在 TLF 和干燥 SS 上的失活动力学遵循 Weibull 模型（0.96≤R≤0.99），但该模型高估了在潮湿 SS 上小剂量 DUV 的失活效果。共聚焦显微镜揭示了在液滴的液-气界面处，细菌形成了一个密集的外层，保护了液滴内部的细胞免受杀菌性 DUV 的伤害。这导致在小剂量 DUV 照射下，潮湿 SS 的失活效果低于预期，且偏离了 Weibull 模型。这些发现可以用于设计针对各种表面条件和应用的有效 DUV LED 消毒策略。
