DNA Damage Kills Bacterial Spores and Cells Exposed to 222-Nanometer UV Radiation

Abstract

This study examined the microbicidal activity of 222-nm UV radiation (UV222), which is potentially a safer alternative to the 254-nm UV radiation (UV254) that is often used for surface decontamination. Spores and/or growing and stationary-phase cells of Bacillus cereus, Bacillus subtilis, Bacillus thuringiensis, Staphylococcus aureus, and Clostridioides difficile and a herpesvirus were all killed or inactivated by UV222 and at lower fluences than with UV254. B. subtilis spores and cells lacking the major DNA repair protein RecA were more sensitive to UV222, as were spores lacking their DNA-protective proteins, the α/β-type small, acid-soluble spore proteins. The spore cores’ large amount of Ca2+-dipicolinic acid (∼25% of the core dry weight) also protected B. subtilis and C. difficile spores against UV222, while spores’ proteinaceous coat may have given some slight protection against UV222. Survivors among B. subtilis spores treated with UV222 acquired a large number of mutations, and this radiation generated known mutagenic photoproducts in spore and cell DNA, primarily cyclobutane-type pyrimidine dimers in growing cells and an α-thyminyl-thymine adduct termed the spore photoproduct (SP) in spores. Notably, the loss of a key SP repair protein markedly decreased spore UV222 resistance. UV222-treated B. subtilis spores germinated relatively normally, and the generation of colonies from these germinated spores was not salt sensitive. The latter two findings suggest that UV222 does not kill spores by general protein damage, and thus, the new results are consistent with the notion that DNA damage is responsible for the killing of spores and cells by UV222. IMPORTANCE Spores of a variety of bacteria are resistant to common decontamination agents, and many of them are major causes of food spoilage and some serious human diseases, including anthrax caused by spores of Bacillus anthracis. Consequently, there is an ongoing need for efficient methods for spore eradication, in particular methods that have minimal deleterious effects on people or the environment. UV radiation at 254 nm (UV254) is sporicidal and commonly used for surface decontamination but can cause deleterious effects in humans. Recent work, however, suggests that 222-nm UV (UV222) may be less harmful to people than UV254 yet may still kill bacteria and at lower fluences than UV254. The present work has identified the damage by UV222 that leads to the killing of growing cells and spores of some bacteria, many of which are human pathogens, and UV222 also inactivates a herpesvirus.

Far UV-C lights and fiber optics induced and selective far UV-C treatment against COVID-19 for fatality-survival tradeoff

“…In-vivomouse skin results consistent with prior investigations in a 3-D human skin tissue in vitro model [8] which also presented imperative skin damage after typical UV254 , but none after UV207. The outcome readily interpretable with respect to limited range of 207 nm UV light which cannot pass through the stratum corneum surface layer of mouse or human skin; on the contrary, broad spectrum UVC from a 254 nm germicidal lamp can swiftly pass through the and dermis and epidermis.…”

“…In [7], extremely low doses of far-UVC light were competently used to deactivate airborne viruses conveyed by aerosols. By use of 222-nm UV radiation (UV222), [8] investigated that how UV222 eradicates cultivating bacteria and spores, and the factors which are imperative for allowing cells and spores to defy the effects of this radiation. UV222 is theoretically a safer alternate to UV254 which is frequently utilized for surface sanitization.…”

Killing of bacterial spores by dodecylamine and its effects on spore inner membrane properties

“…2016; Taylor et al . 2020). Spore purification included centrifugation through 50 and 45% Histodenz solutions for CaDPA‐replete and CaDPA‐less spores, respectively, as described above; the yields of purified spores of the different C. difficile different strains were all ~7 × 10 8 spores from each plate.…”

“…However, 10 µl aliquots of dilutions were applied in a grid in an anaerobic cabinet to prereduced brain heart infusion agar plates containing 1·9 mmol l −1 taurocholic acid (TA) and 1 g l −1 l ‐cysteine as described (Taylor et al . 2020). These plates were incubated at 37°C in an anaerobic cabinet with a gas of 85% N 2 , 5% CO 2 and 10% H 2 until no more colonies appeared (14–24 h) and colonies were counted.…”

Microbiological Evaluation of the Disinfecting Potential of UV-C and UV-C Plus Ozone Generating Robots

“…This last study concluded that low-intensity levels equivalent to 2 mJ cm −2 of UV-C 222-nm on the center of the irradiation target in public locations might represent a safe and efficient methodology for limiting the transmission and spread of airborne-mediated microbial diseases. This same UV-C 222-nm fluence was demonstrated to produce enough DNA damage to kill B. subtilis endospores [ 26 ]. Although this particular study also reported skin damage after typical UV-C 254-nm , none after UV-C 207-nm [ 26 ], our robots were designed to be used exclusively in the absence of people, and the sweeping of the entire room by the robot achieved a cumulative effect of additional radiation in successive passes.…”