Application of 233 nm far-UVC LEDs for eradication of MRSA and MSSA and risk assessment on skin models

Effect of Extended Defects on AlGaN Quantum Dots for Electron-Pumped Ultraviolet Emitters

We study the origin of bimodal emission in AlGaN/AlN QD superlattices displaying a high internal quantum efficiency (around 50%) in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-like domains with deformed QD layers, which originate at the first AlN buffer/superlattice interface and propagate vertically. The cones originate at a 30°-faceted shallow pit in the AlN, which appears to be associated with a threading dislocation that produces strong shear strain. The cone-like structures present Ga enrichment at the boundaring facets and larger QDs within the conic domain. The bimodality of the luminescence is attributed to the differing dot size and composition within the cones and at the faceted boundaries, which is confirmed by the correlation of microscopy results and Schrödinger-Poisson calculations.

Assessing the safety of new germicidal far-UVC technologies

The COVID-19 pandemic underscored the crucial importance of enhanced indoor air quality control measures to mitigate the spread of respiratory pathogens. Far-UVC is a type of germicidal ultraviolet technology, with wavelengths between 200 and 235 nm, that has emerged as a highly promising approach for indoor air disinfection. Due to its enhanced safety compared to conventional 254 nm upper-room germicidal systems, far-UVC allows for whole-room direct exposure of occupied spaces, potentially offering greater efficacy, since the total room air is constantly treated. While current evidence supports using far-UVC systems within existing guidelines, understanding the upper safety limit is critical to maximizing its effectiveness, particularly for the acute phase of a pandemic or epidemic when greater protection may be needed. This review article summarizes the substantial present knowledge on far-UVC safety regarding skin and eye exposure and highlights research priorities to discern the maximum exposure levels that avoid adverse effects. We advocate for comprehensive safety studies that explore potential mechanisms of harm, generate action spectra for crucial biological effects and conduct high-dose, long-term exposure trials. Such rigorous scientific investigation will be key to determining safe and effective levels for far-UVC deployment in indoor environments, contributing significantly to future pandemic preparedness and response.

Efficacy of 233 nm LED far UV-C-radiation against clinically relevant bacterial strains in the phase 2/ step 2 in vitro test on basis of EN 14561 and on an epidermis cell model

INTRODUCTION

Healthcare-acquired infections and overuse of antibiotics are a common problem. Rising emergence of antibiotic and antiseptic resistances requires new methods of microbial decontamination or decolonization as the use of far-UV-C radiation.

METHODS

The microbicidal efficacy of UV-C radiation (222 nm, 233 nm, 254 nm) was determined in a quantitative carrier test and on 3D-epidermis models against Staphylococcus (S.) aureus, S.epidermidis, S.haemolyticus, S.lugdunensis, Klebsiella pneumoniae, and Pseudomonas aeruginosa. To mimic realistic conditions, sodium chloride solution, mucin, albumin, artificial saliva, artificial wound exudate and artificial sweat were used.

RESULTS

In sodium chloride solution, irradiation with a dose of 40 mJ/cm2 (233 nm) was sufficient to achieve 5 lg reduction independent of bacteria genus or species. In artificial sweat, albumin and artificial wound exudate, a reduction >3 lg was reached for most of the bacteria. Mucin and artificial saliva decreased the reduction to <2 lg. On 3D epidermis models, reduction was lower than in the carrier test.

CONCLUSION

UV-C radiation at 233 nm was proven to be efficient in bacteria inactivation independent of genus or species thus being a promising candidate for clinical use in the presence of humans and on skin/mucosa.

Effectiveness of Umonium38 against Burkholderia pseudomallei, Escherichia coli, Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus aureus (MRSA)

AIMS

We investigated the antibacterial efficacy of Umonium38 and Virkon® against Burkholderia pseudomallei, Escherichia coli, Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus aureus (MRSA) up to 14 days following treatment.

METHODS AND RESULTS

Umonium38 was diluted to 0.5%, 1.0%, 1.5%, 2.0%, 2.5% and 3%, tested against the bacterial strains at various contact times (15 min to 24 h), and incubated for up to 14 days. A minimum concentration of 0.5% Umonium38 with a contact time of 15 min effectively killed approximately 108 CFU/ml of all four bacterial species. No growth was observed on agar plates from day 0 until day 14 for all six concentrations. The bacteria were also inactivated by a 30-minute treatment time using Virkon® 1% solution.

CONCLUSIONS

Umonium38 effectively inactivates B. pseudomallei, E. coli, P. aeruginosa and MRSA at a concentration of ≥ 0.5% with a contact time of at least 15 min. The antimicrobial effect of Umonium38 remained for 14 days.

Significance of melanin distribution in the epidermis for the protective effect against UV light

Melanin, the most abundant skin chromophore, is produced by melanocytes and is one of the key components responsible for mediating the skin's response to ultraviolet radiation (UVR). Because of its antioxidant, radical scavenging, and broadband UV absorbing properties, melanin reduces the penetration of UVR into the nuclei of keratinocytes. Despite its long-established photoprotective role, there is evidence that melanin may also induce oxidative DNA damage in keratinocytes after UV exposure and therefore be involved in the development of melanoma. The present work aimed at evaluating the dependence of UV-induced DNA damage on melanin content and distribution, using reconstructed human epidermis (RHE) models. Tanned and light RHE were irradiated with a 233 nm UV-C LED source at 60 mJ/cm2 and a UV lamp at 3 mJ/cm2. Higher UV-mediated free radicals and DNA damage were detected in tanned RHE with significantly higher melanin content than in light RHE. The melanin distribution in the individual models can explain the lack of photoprotection. Fluorescence lifetime-based analysis and Fontana-Masson staining revealed a non-homogeneous distribution and absence of perinuclear melanin in the tanned RHE compared to the in vivo situation in humans. Extracellularly dispersed epidermal melanin interferes with photoprotection of the keratinocytes.

Enhanced vegetable production in hydroponic systems using decontamination of closed circulating fluid

While plant microorganisms can promote plants by producing natural antibiotics, they can also be vectors for disease transmission. Contamination from plant management practices and the surrounding environment can adversely affect plants, leading to infections and hindered growth due to microbial competition for nutrients. The recirculation of nutrient-rich fluids can facilitate the transport of microorganisms between vegetables in the hydroponic production system. This issue can be addressed through the application of the decontamination method in the hydroponic liquid. Ultraviolet light (UV-C) has been employed for microbiology, and its effects on lettuce were evaluated in this study. This study aims to assess the effectiveness of a decontamination system using UV-C in hydroponic solutions during nutrient recirculation in hydroponics. We evaluated the time required for lettuce plants to reach their maximum height, as well as their pigment content, phenolic compounds, antioxidant capacity, and micro and macronutrient levels. The evaluation was conducted under two photoperiods (18 and 20 hours) in lettuce samples exposed to UV-C in the hydroponic fluid, with control groups not exposed to UV-C. The application of the UV-C decontamination system in hydroponic circulation water containing nutrients accelerated plant growth while maintaining nutritional values equal to or higher than those in the control groups without such a system. The results of microorganism control highlight the potential application of this technique for enhancing and expediting vegetable production. This approach reduces production time and enhances nutrient absorption and the content of certain compounds and minerals.

Irradiation of human oral mucosa by 233 nm far UV-C LEDs for the safe inactivation of nosocomial pathogens

The inactivation of multi resistant pathogens is an important clinical need. One approach is UV-C irradiation, which was previously not possible in vivo due to cytotoxicity. Recently, far UV-C irradiation at λ < 240 nm was successfully used on skin with negligible damage. A potential application site is the nasal vestibule, where MRSA accumulates and cannot be treated using antiseptics. We irradiated 3D mucosa models and excised human mucosa with 222 and 233 nm far UV-C in comparison to 254 nm and broadband UV-B. Eradication efficiency was evaluated by counting colony forming units; irritation potential was evaluated by hen's egg-chorioallantoic membrane assay and trans epithelial electrical resistance; cell viability was assessed by MTT. DNA damage and cell protective mechanisms were evaluated immunohistopathologically. On mucosa models, MRSA reduced by ≈ 5 log10 for 60 mJ/cm2 irradiation at 233 nm. A slightly increased cell viability was observed after 24 h. Lower doses showed lower irritation potential than the positive controls or commercial mouthwash, while 80 mJ/cm2 had strong irritation potential. DNA damage occurred only superficially and decreased after 24 h. On excised human mucosa, < 10% of keratinocytes were affected after 150 mJ/cm2 222 nm or 60 mJ/cm2 233 nm.

Skin optical properties from 200 to 300 nm support far UV-C skin-safety in vivo

The growing threat of multi-drug resistant pathogens and airborne microbial diseases has highlighted the need to improve or develop novel disinfection methods for clinical environments. Conventional ultraviolet C (UV-C) lamps effectively inactivate microorganisms but are harmful to human skin and eyes upon exposure. The use of new 233 nm far UV-C LEDs as an antiseptic can overcome those limitations. In this research, the light penetration into the skin was elucidated for the UV-C region (<300 nm) by measuring the scattering and absorption of skin layers and inverse Monte Carlo simulation, and further confirmed by the first clinical pilot trial in which healthy volunteers were irradiated with a dose of 60 mJ/cm2 at 233 nm. The radiation is strongly absorbed in the stratum corneum, resulting in minimal skin damage without inducing inflammatory responses. The results suggest that 233 nm far UV-C light emitting diodes (LEDs) could effectively inactivate microorganisms, while being safe and soft for the skin.

Far-UVC- and UVB-induced DNA damage depending on skin type

Far-UVC radiation sources of wavelengths 222 nm and 233 nm represent an interesting potential alternative for the antiseptic treatment of the skin due to their high skin compatibility. Nevertheless, no studies on far-UVC-induced DNA damage in different skin types have been published to date, which this study aims for. After irradiating the skin with far-UVC of the wavelengths 222 and 233 nm as well as broadband UVB, the tissue was screened for cyclobutane pyrimidine dimer-positive (CPD+ ) cells using immunohistochemistry. The epidermal DNA damage was lower in dark skin types than in fair skin types after irradiation at 233 nm. Contrary to this, irradiation at 222 nm caused no skin type-dependent differences, which can be attributed to the decreased penetration depth of radiation. UVB showed the relatively strongest differences between light and dark skin types when using a suberythemal dose of 3 mJ/cm2 . As melanin is known for its photoprotective effect, we evaluated the ratio of melanin content in the stratum basale and stratum granulosum in samples of different skin types using two-photon excited fluorescence lifetime imaging (TPE-FLIM) finding a higher ratio up to skin type IV-V. As far-UVC is known to penetrate only into the upper layers of the viable skin, the aforementioned melanin ratio could explain the less pronounced differences between skin types after irradiation with far-UVC compared to UVB.

Evaluation of DNA lesions and radicals generated by a 233 nm far-UVC LED in superficial ex vivo skin wounds

The application of a far-ultraviolet C (UVC) light emitting diode (LED) of 233 nm showed significant bactericidal efficacy at an applied dose between 20 and 80 mJ cm-2 as reported recently. In addition, only minor epidermal DNA lesions were observed in ex vivo human skin and in vitro epidermal models <10% of the minimal erythema dose of UVB radiation. To broaden the potential range of applications of such systems, e.g. to include postoperative application on wounds for the purpose of decontamination, we assessed how a disruption of normal anatomic skin structure and function influences the skin damage induced by light from 233 nm far-UVC LEDs. Thus, we induced superficial skin wounds by mechanical detachment of the stratum corneum in ex vivo human skin. Barrier-disruption of the skin could be successfully determined by measuring an increase in the transepidermal water loss (TEWL) and the stratum corneum loss could be determined morphologically by 2-photon microscopy (2-PM). After far-UVC irradiation of the skin, we screened the tissue for the development of cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts (6-4PPs). The abundance of DNA lesions was elevated in wound skin in comparison to intact skin after irradiation with far-UVC. However, no increase in DNA lesions was detected when artificial wound exudate consisting of cell culture medium and serum was applied to the disrupted skin surface prior to irradiation. This effect agrees with the results of ray tracing simulations of the absorption of far-UVC light incident on a superficial skin wound. Interestingly, no significant deviations in radical formation between intact skin and superficially wounded skin were detected after far-UVC irradiation as analyzed by electron paramagnetic resonance (EPR) spectroscopy. In conclusion, 233 nm LED light at a dose of 60 mJ/cm2 could be applied safely on superficial wounds for the purpose of skin antisepsis as long as the wounds are covered with wound fluid.

Semantic modeling of cell damage prediction: a machine learning approach at human-level performance in dermatology

Machine learning is transforming the field of histopathology. Especially in classification related tasks, there have been many successful applications of deep learning already. Yet, in tasks that rely on regression and many niche applications, the domain lacks cohesive procedures that are adapted to the learning processes of neural networks. In this work, we investigate cell damage in whole slide images of the epidermis. A common way for pathologists to annotate a score, characterizing the degree of damage for these samples, is the ratio between healthy and unhealthy nuclei. The annotation procedure of these scores, however, is expensive and prone to be noisy among pathologists. We propose a new measure of damage, that is the total area of damage, relative to the total area of the epidermis. In this work, we present results of regression and segmentation models, predicting both scores on a curated and public dataset. We have acquired the dataset in collaborative efforts with medical professionals. Our study resulted in a comprehensive evaluation of the proposed damage metrics in the epidermis, with recommendations, emphasizing practical relevance for real world applications.

Phenotypic Variation in Clinical S. aureus Isolates Did Not Affect Disinfection Efficacy Using Short-Term UV-C Radiation

Pigmentation, catalase activity and biofilm formation are virulence factors that cause resistance of Staphylococcus aureus to environmental stress factors including disinfectants. In recent years, automatic UV-C room disinfection gained greater importance in enhanced disinfection procedures to improve disinfection success in hospitals. In this study, we evaluated the effect of naturally occurring variations in the expression of virulence factors in clinical S. aureus isolates on tolerance against UV-C radiation. Quantification of staphyloxanthin expression, catalase activity and biofilm formation for nine genetically different clinical S. aureus isolates as well as reference strain S. aureus ATCC 6538 were performed using methanol extraction, a visual approach assay and a biofilm assay, respectively. Log₁₀ reduction values (LRV) were determined after irradiation of artificially contaminated ceramic tiles with 50 and 22 mJ/cm² UV-C using a commercial UV-C disinfection robot. A wide variety of virulence factor expression was observed, indicating differential regulation of global regulatory networks. However, no direct correlation with the strength of expression with UV-C tolerance was observed for either staphyloxanthin expression, catalase activity or biofilm formation. All isolates were effectively reduced with LRVs of 4.75 to 5.94. UV-C disinfection seems therefore effective against a wide spectrum of S. aureus strains independent of occurring variations in the expression of the investigated virulence factors. Due to only minor differences, the results of frequently used reference strains seem to be representative also for clinical isolates in S. aureus.

UV radiation sensitivity of bacteriophage PhiX174 - A potential surrogate for SARS-CoV-2 in terms of radiation inactivation

To minimize health risks, surrogates are often employed to reduce experiments with pathogenic microorganisms and the associated health risk. Due to structural similarities between the enveloped RNA-viruses SARS-CoV-2 and Phi6, the latter has been established as a nonpathogenic coronavirus surrogate for many applications. However, large discrepancies in the UV log-reduction doses between SARS-CoV-2 and Phi6 necessitate the search for a better surrogate for UV inactivation applications. A literature study provided the bacteriophage PhiX174 as a potentially more suitable nonpathogenic coronavirus surrogate candidate. In irradiation experiments, the sensitivity of PhiX174 was investigated upon exposure to UV radiation of wavelengths 222 nm (Far-UVC), 254 nm (UVC), 302 nm (broad-band UVB), 311 nm (narrow-band UVB) and 366 nm (UVA) using a plaque assay. The determined log-reduction doses for PhiX174 were 1.3 mJ/cm2 @ 222 nm, 5 mJ/cm2 @ 254 nm, 17.9 mJ/cm2 @ 302 nm, 625 mJ/cm2 @ 311 nm and 42.5 J/cm2 @ 366 nm. The comparison of these results with published log-reduction doses of SARS-CoV-2 in the same spectral region, led to the conclusion that the bacteriophage PhiX174 exhibits larger log-reduction doses than SARS-CoV-2, nevertheless, it is a better UV-surrogate at 222 nm (Far-UVC), 254 nm (UVC) and 302 nm (UVB) than the often applied Phi6.

Different biological effects of exposure to far-UVC (222 nm) and near-UVC (254 nm) irradiation

Ultraviolet C (UVC) light has long been used as a sterilizing agent, primarily through devices that emit at 254 nm. Depending on the dose and duration of exposure, UV 254 nm can cause erythema and photokeratitis and potentially cause skin cancer since it directly modifies nitrogenated nucleic acid bases. Filtered KrCl excimer lamps (emitting mainly at 222 nm) have emerged as safer germicidal tools and have even been proposed as devices to sterilize surgical wounds. All the studies that showed the safety of 222 nm analyzed cell number and viability, erythema generation, epidermal thickening, the formation of genetic lesions such as cyclobutane pyrimidine dimers (CPDs) and pyrimidine-(6-4)-pyrimidone photoproducts (6-4PPs) and cancer-inducing potential. Although nucleic acids can absorb and be modified by both UV 254 nm and UV 222 nm equally, compared to UV 254 nm, UV 222 nm is more intensely absorbed by proteins (especially aromatic side chains), causing photooxidation and cross-linking. Here, in addition to analyzing DNA lesion formation, for the first time, we evaluated changes in the proteome and cellular pathways, reactive oxygen species formation, and metalloproteinase (MMP) levels and activity in full-thickness in vitro reconstructed human skin (RHS) exposed to UV 222 nm. We also performed the longest (40 days) in vivo study of UV 222 nm exposure in the HRS/J mouse model at the occupational threshold limit value (TLV) for indirect exposure (25 mJ/cm²) and evaluated overall skin morphology, cellular pathological alterations, CPD and 6-4PP formation and MMP-9 activity. Our study showed that processes related to reactive oxygen species and inflammatory responses were more altered by UV 254 nm than by UV 222 nm. Our chronic in vivo exposure assay using the TLV confirmed that UV 222 nm causes minor damage to the skin. However, alterations in pathways related to skin regeneration raise concerns about direct exposure to UV 222 nm.

Far-UVC Radiation for Disinfecting Hands or Gloves?

(1) Background: Far-UVC radiation in the spectral range 200-230 nm has, according to previous findings, a strong antimicrobial effect on pathogens, but exhibits hardly any harmful effect on human skin. Therefore, the present study will discuss whether such radiation could also be suitable for hand disinfection in the healthcare sector. (2) Methods: Hands and gloves were microbially contaminated and exposed to radiation from a 222 nm krypton-chloride-excimer lamp. The applied doses were 23 mJ/cm2 and 100 mJ/cm2, respectively. Irradiated and non-irradiated hands and gloves were pressed onto agar plates and colonies were counted and compared after 24 h of incubation. For comparison, we also treated hands and gloves with a commercial liquid alcohol-based disinfectant. (3) Results: On the hand, the 23 mJ/cm2 resulted in the reduction of the observed colonies on the agar plates by one log level. For the gloves irradiated with 100 mJ/cm2, a colony reduction of 1.3 log levels was recorded. In the comparative experiments with the commercial disinfectant, a colony reduction of 1.9 and approximately one log level was observed on hand and gloves, respectively. (4) Conclusion: In both cases, far-UVC radiation provided a considerable reduction in microorganisms. However, compared to published far-UVC irradiation results in suspensions, the disinfection success on hands and gloves was rather low. With regard to the irradiation limits currently existing in the European Union, multiple daily hand disinfection with far-UVC radiation is actually legally not possible at present, but the thresholds are currently under discussion and could change in the future. Far-UVC disinfection of hands in gloves seems theoretically possible if attention is paid to potential perforations in the gloves.

Sensitivity of influenza virus to ultraviolet irradiation

BACKGROUND

The measures implemented against the coronavirus pandemic also led to a sharp decline in influenza infections in the 2020/2021 flu season. In the meantime, however, the number of influenza infections has risen again; it is known from history that influenza viruses can also trigger severe pandemics. Therefore, we investigated the efficacy of ultraviolet radiation in the spectral range of 200-400 nm for inactivating influenza viruses.

MATERIALS AND METHODS

The scientific literature was searched for published ultraviolet (UV) irradiation experiments with influenza viruses and the results were standardized by determining the lg-reduction dose. The results were then sorted and analyzed by virus type and wavelength as far as possible.

RESULTS

The scope of the published data sets was limited and revealed large variations with regard to the lg-reduction dose. Only for experiments with influenza viruses in liquid media in the UVC spectral range around 260 nm - the emission range of commonly-used mercury vapor lamps - was there sufficient data to compare virus types. No significant difference between the virus (sub-) types was observed. The lg-reduction dose in this spectral range is 1.75 mJ/cm² (median). It was also shown that influenza viruses are particularly sensitive in the far-UVC spectral range (200-230 nm).

CONCLUSION

UVC, including far-UVC, is suited for influenza virus inactivation as long as the viruses are in UVC-transparent materials. A large difference in the UV sensitivity of different influenza viruses from the last approx. 100 years could not be detected. Thus, it is reasonable to assume that future influenza viruses will also be similarly UV-sensitive or that UV can also inactivate new influenza viruses.