Evaluation of efficacy of ultraviolet (UV) radiation against viruses and bacteria

The resistance of virus and bacteria to UV radiation was examined^40–42. Virus (IAV) was mixed with saline or artificial mucus (CMC, GG, XG, or gelatin) prior to UV radiation exposure. A 30-µl volume of virus/artificial mucus (final virus titre; 5.0 × 10⁶ FFU/ml) was irradiated at a dose of 0, 2.25, 4.5, or 6.75 mJ/cm² before dilution with 1350 µl of MEM. The virus was then titrated. The test was also conducted with sputum samples with or without pronase treatment.

E. coli cells were mixed with saline or artificial mucus, and 30 µl of bacteria/artificial mucus (final viable count: 1.0 × 10⁷ CFU/ml) were irradiated at a dose of 0, 1.13, 2.25, or 3.38 mJ/cm² before dilution with 1350 µl MEM. The viable count was then determined.

The titre/viable count ratio was defined as the ratio of titre/viable count measured after to that measured before exposure to UV. Three independent experiments were performed and the results are expressed as mean ± standard deviation.