Inactivation of bacterial pathogens following exposure to light from a 405-nanometer light-emitting diode array

Decontamination of patient bathroom surfaces with 405 nm violet-blue light irradiation in a real-life setting

BACKGROUND

Irradiation with violet-blue light (VBL), in the spectrum of 405-450 nm, has been reported to be effective against pathogenic bacteria.

AIM

To investigate whether VBL irradiation could reduce the level of surface contamination at seven shared patient bathrooms in two wards at a hospital in Sweden.

METHODS

Repeated sampling of five separate surfaces (door handle, tap water handle, floor, toilet seat, and toilet armrest) was performed in the bathrooms where 405 nm light-emitting diode spotlights had been installed. A prospective study with a cross-over design was carried out, which included two study periods, first with the spotlights either switched on or off and a second study period with the opposite spotlight status.

FINDINGS

In total, 665 surface samples were collected during the study (133 samples per surface). Bacterial growth was found in 84% of all samples. The most common findings were coagulase-negative staphylococci and Bacillus spp. The median number of colony-forming units (cfu)/cm2 was 15 (interquartile range: 5-40) for all surfaces. In our main outcome, mean cfu/cm2 of all surfaces in a bathroom, no difference was observed with or without VBL. Clean surfaces (<5 cfu/cm2) were more commonly observed in bathrooms with VBL, also when controlling for confounding factors. No difference was observed in the number of heavily contaminated surfaces.

CONCLUSION

This study did not safely demonstrate an additive effect on bacterial surface levels when adding VBL to routine cleaning in shared patient bathrooms.

Biofilm inactivation using LED systems emitting germicidal UV and antimicrobial blue light

Biofilms have been widely detected in water distribution and water storage systems posing potential risks to drinking water safety by harboring and shedding pathogens. Light-based disinfection methods, such as germicidal ultraviolet (UV) and antimicrobial blue light (aBL), could serve as non-chemical alternatives for biofilm control. This study investigated the inactivation of pure-culture Pseudomonas aeruginosa biofilms and mixed-culture biofilms using three distinct light-based disinfection methods: a low-pressure (LP) UV lamp emitting at 254 nm, a UV light emitting diode (LED) at 270 nm, and an aBL LED at 405 nm. The biofilms were developed on three commonly used materials including polycarbonate (PC), polytetrafluoroethylene (PTFE), and polyvinyl chloride (PVC), to assess the impact of surface characteristics on light-based biofilm inactivation. Our findings show that all selected devices can effectively inactivate pure-culture and mixed-culture biofilms. While both UV devices (LP UV lamp and UV LED) provided significant inactivation at lower fluences (>1 log reduction at 20 mJ/cm2), aBL LED achieved significant inactivation at higher fluences for pure culture (maximum log reduction of 3.8 ± 0.5 at > 200,000 mJ/cm2). Inactivation performance also varied with surface materials, likely attributed to different surface properties including roughness, hydrophobicity, and surface charge. This study provides important information on using light-based technologies for biofilm control and highlights the effect of surface materials on their inactivation performance.

Bacterial reduction and temperature increase of titanium dental implant models treated with a 445 nm diode laser: an in vitro study

In this in vitro study, the use of a 445 nm diode laser was investigated for the decontamination of titanium dental implants. Different irradiation protocols and the effect of repetitive laser irradiation on temperature increase and decontamination efficacy were evaluated on titanium implant models. An automated setup was developed to realize a scanning procedure for a full surface irradiation to recapitulate a clinical treatment. Three irradiation parameter sets A (continuous wave, power 0.8 W, duty cycle (DC) 100%, and 5 s), B (pulsed mode, DC 50%, power 1.0 W, and 10 s), and C (pulsed mode, DC 10%, power 3.0 W, and 20 s) were used to treat the rods for up to ten consecutive scans. The resulting temperature increase was measured by a thermal imaging camera and the decontamination efficacy of the procedures was evaluated against Escherichia coli and Staphylococcus aureus, and correlated with the applied laser fluence. An implant's temperature increase of 10 °C was set as the limit accepted in literature to avoid thermal damage to the surrounding tissue in vivo. Repeated irradiation of the specimens resulted in a steady increase in temperature. Parameter sets A and B caused a temperature increase of 11.27 ± 0.81 °C and 9.90 ± 0.37 °C after five consecutive laser scans, respectively, while parameter set C resulted in a temperature increase of only 8.20 ± 0.53 °C after ten surface scans. The microbiological study showed that all irradiation parameter sets achieved a complete bacterial reduction (99.9999% or 6-log10) after ten consecutive scans, however only parameter set C did not exceed the temperature threshold. A 445 nm diode laser can be used to decontaminate dental titanium rods, and repeated laser irradiation of the contaminated areas increases the antimicrobial effect of the treatment; however, the correct choice of parameters is needed to provide adequate laser fluence while preventing an implant's temperature increase that could cause damage to the surrounding tissue.

Light-activated conjugated polymer nanoparticles to defeat pathogens associated with bovine mastitis

Bovine mastitis (BM) represents a significant challenge in the dairy industry. Limitations of conventional treatments have prompted the exploration of alternative approaches, such as photodynamic inactivation (PDI). In this study, we developed a PDI protocol to eliminate BM-associated pathogens using porphyrin-doped conjugated polymer nanoparticles (CPN). The PDI-CPN protocol was evaluated in four mastitis isolates of Staphylococcus and in a hyper-biofilm-forming reference strain. The results in planktonic cultures demonstrated that PDI-CPN exhibited a bactericidal profile upon relatively low light doses (∼9.6 J/cm2). Furthermore, following a seven-hour incubation period, no evidence of cellular reactivation was observed, indicating a highly efficient post-photodynamic inactivation effect. The successful elimination of bacterial suspensions encouraged us to test the PDI-CPN protocol on mature biofilms. Treatment using moderate light dose (∼64.8 J/cm2) reduced biofilm biomass and metabolic activity by up to 74% and 88%, respectively. The impact of PDI-CPN therapy on biofilms was investigated using scanning electron microscopy (SEM), which revealed nearly complete removal of the extracellular matrix and cocci. Moreover, ex vivo studies conducted on bovine udder skin demonstrated the efficacy of the therapy in eliminating bacteria from these scaffolds and its potential as a prophylactic method. Notably, the histological analysis of skin revealed no signs of cellular degeneration, suggesting that the protocol is safe and effective for BM treatment. Overall, this study demonstrates the potential of PDI-CPN in treating and preventing BM pathogens. It also provides insights into the effects of PDI-CPN on bacterial growth, metabolism, and survival over extended periods, aiding the development of effective control strategies and the optimization of future treatments.

Ascorbic acid potentiates photodynamic inactivation mediated by octyl gallate and blue light for rapid eradication of planktonic bacteria and biofilms

This study reported for the first time that Ascorbic acid (AA) could appreciably boost the efficiency of Octyl gallate (OG)-mediated photodynamic inactivation (PDI) on Escherichia coli and Staphylococcus aureus in planktonic and biofilm states. The combination of OG (0.075 mM) and AA (200 mM) with 420 nm blue light (212 mW/cm2) led to a >6 Log killing within only 5 min for E. coli and S. aureus and rapid eradication of biofilms. The mechanism of action appears to be the generation of highly toxic hydroxyl radicals (•OH) via photochemical pathways. OG was exposed to BL irradiation to generate various reactive oxygen radicals (ROS) and the addition of AA could transform singlet oxygen (1O2) into hydrogen peroxide (H2O2), which could further react with AA to generate enormous •OH. These ROS jeopardized bacteria and biofilms by nonspecifically attacking various biomacromolecules. Overall, this PDI strategy provides a powerful microbiological decontamination modality to guarantee safe food products.

Microbial reduction of prebagged human plasma using 405 nm light and its effects on coagulation factors

Bacterial contamination is the most prevalent infectious complication of blood transfusion in the developed world. To mitigate this, several ultraviolet light-based pathogen reduction technologies (PRTs), some of which require photo-chemicals, have been developed to minimize infection transmission. Relative to UV light, visible 405-nm light is safer and has shown potential to be developed as a PRT for the in situ treatment of ex vivo human plasma and platelet concentrates, without the need for photo-chemicals. This study investigates the effect of 405-nm light on human plasma, with focus on the compatibility of antimicrobial light doses with essential plasma clotting factors. To determine an effective antimicrobial dose that is compatible with plasma, prebagged human plasma (up to 300 mL) was seeded with common microbial contaminants and treated with increasing doses of 405-nm light (16 mW cm-2; ≤ 403 J cm-2). Post-exposure plasma protein integrity was investigated using an AOPP assay, in vitro coagulation tests, and ELISA-based measurement of fibrinogen and Protein S. Microbial contamination in 300 mL prebagged human plasma was significantly reduced (P ≤ 0.05) after exposure to ≤ 288 J cm-2, with microbial loads reduced by > 96.2%. This dose did not significantly affect the plasma protein quality parameters tested (P > 0.05). Increased doses (≥ 345 J cm-2) resulted in a 4.3% increase in clot times with no statistically significant change in protein activity or levels. Overall, this study has demonstrated that the effective microbicidal 405 light dose shows little to no negative effect on plasma quality.

Enhanced antimicrobial efficacy and energy efficiency of low irradiance 405-nm light for bacterial decontamination

Due to its increased safety over ultraviolet light, there is interest in the development of antimicrobial violet-blue light technologies for infection control applications. To ensure compatibility with exposed materials and tissue, the light irradiances and dose regimes used must be suitable for the target application. This study investigates the antimicrobial dose responses and germicidal efficiency of 405 nm violet-blue light when applied at a range of irradiance levels, for inactivation of surface-seeded and suspended bacteria. Bacteria were seeded onto agar surfaces (101-108 CFUplate-1) or suspended in PBS (103-109 CFUmL-1) and exposed to increasing doses of 405-nm light (≤ 288 Jcm-2) using various irradiances (0.5-150 mWcm-2), with susceptibility at equivalent light doses compared. Bacterial reductions ≥ 96% were demonstrated in all cases for lower irradiance (≤ 5 mWcm-2) exposures. Comparisons indicated, on a per unit dose basis, that significantly lower doses were required for significant reductions of all species when exposed at lower irradiances: 3-30 Jcm-2/0.5 mWcm-2 compared to 9-75 Jcm-2/50 mWcm-2 for low cell density (102 CFUplate-1) surface exposures and 22.5 Jcm-2/5 mWcm-2 compared to 67.5 Jcm-2/150 mWcm-2 for low density (103 CFUmL-1) liquid exposures (P ≤ 0.05). Similar patterns were observed at higher densities, excluding S. aureus exposed at 109 CFUmL-1, suggesting bacterial density at predictable levels has minimal influence on decontamination efficacy. This study provides fundamental evidence of the greater energy efficacy of 405-nm light for inactivation of clinically-significant pathogens when lower irradiances are employed, further supporting its relevance for practical decontamination applications.

Evaluation of Phototoxicity of Short-Wavelength Laser Light Utilizing PCNA Accumulation

In recent years, diseases such as age-related macular degeneration and retinal pigment degeneration caused by excessive exposure to short-wavelength visible light have become significant concerns. With the aim of quantitatively evaluating the toxicity of short-wavelength light, proliferating cell nuclear antigen (PCNA) accumulation at the irradiation site was investigated using live cell imaging techniques to irradiate individual living cells with short-wavelength laser light. By examining the dependency of PCNA accumulation on the irradiation site within the cells and their cell cycle, it was observed that PCNA accumulation occurred only when the cell nucleus of cells in the S phase of the cell cycle was irradiated. We investigated the accumulation of PCNA at the laser irradiation site using laser light at wavelengths of 405 nm and 375 nm, with intensities ranging from 0.5 μW to 9.0 μW. The results confirmed an increase in PCNA accumulation with increasing intensity, and a higher accumulation was observed with laser light irradiation at a wavelength of 375 nm compared to 405 nm. By comparing the PCNA accumulation and 24 h cell viability, we demonstrated the feasibility of quantitatively assessing laser light toxicity through the measurement of PCNA accumulation.

Volatile Fatty Acids Effective as Antibacterial Agents against Three Enteric Bacteria during Mesophilic Anaerobic Incubation

The antibacterial effects of a selection of volatile fatty acids (acetic, propionic, butyric, valeric, and caproic acids) relevant to anaerobic digestion were investigated at 1, 2 and 4 g/L. The antibacterial effects were characterised by the dynamics of Enterococcus faecalis NCTC 00775, Escherichia coli JCM 1649 and Klebsiella pneumoniae A17. Mesophilic anaerobic incubation to determine the minimum bactericidal concentration (MBC) and median lethal concentration of the VFAs was carried out in Luria Bertani broth at 37 °C for 48 h. Samples collected at times 0, 3, 6, 24 and 48 h were used to monitor bacterial kinetics and pH. VFAs at 4 g/L demonstrated the highest bactericidal effect (p < 0.05), while 1 g/L supported bacterial growth. The VFA cocktail was the most effective, while propionic acid was the least effective. Enterococcus faecalis NCTC 00775 was the most resistant strain with the VFAs MBC of 4 g/L, while Klebsiella pneumoniae A17 was the least resistant with the VFAs MBC of 2 g/L. Allowing a 48 h incubation period led to more log decline in the bacterial numbers compared to earlier times. The VFA cocktail, valeric, and caproic acids at 4 g/L achieved elimination of the three bacteria strains, with over 7 log10 decrease within 48 h.

Predicting Antibiotic Resistance and Assessing the Risk Burden from Antibiotics: A Holistic Modeling Framework in a Tropical Reservoir

Predicting the hotspots of antimicrobial resistance (AMR) in aquatics is crucial for managing associated risks. We developed an integrated modeling framework toward predicting the spatiotemporal abundance of antibiotics, indicator bacteria, and their corresponding antibiotic-resistant bacteria (ARB), as well as assessing the potential AMR risks to the aquatic ecosystem in a tropical reservoir. Our focus was on two antibiotics, sulfamethoxazole (SMX) and trimethoprim (TMP), and on Escherichia coli (E. coli) and its variant resistant to sulfamethoxazole-trimethoprim (EC_SXT). We validated the predictive model using withheld data, with all Nash-Sutcliffe efficiency (NSE) values above 0.79, absolute relative difference (ARD) less than 25%, and coefficient of determination (R2) greater than 0.800 for the modeled targets. Predictions indicated concentrations of 1-15 ng/L for SMX, 0.5-5 ng/L for TMP, and 0 to 5 (log10 MPN/100 mL) for E. coli and -1.1 to 3.5 (log10 CFU/100 mL) for EC_SXT. Risk assessment suggested that the predicted TMP could pose a higher risk of AMR development than SMX, but SMX could possess a higher ecological risk. The study lays down a hybrid modeling framework for integrating a statistic model with a process-based model to predict AMR in a holistic manner, thus facilitating the development of a better risk management framework.

Ameliorative and Disinfection Effects of Ultraviolet-C Radiation on Experimentally Induced and Infected Skin Wounds: A Mice Model Study

Only ultraviolet-C (UV-C) from UV lights, which are emitted by the sun and absorbed by the atmosphere's ozone layer, does not reach the Earth's surface. UV-C is a powerful disinfection method that is commonly used to sterilize fluids, air, and surfaces. There is a little knowledge of the effects of UV-C radiation on living bodies. The purpose of this study is to examine the ameliorative effect of UV-C on skin lesions in mice that have been experimentally created and infected with Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus sp. In total, 32 mice were used, and 4 mm skin defects were created and lesions infected with bacteria. Half of the mice in each group were treated with 254 nm UV-C twice a day for 4 days before being euthanatized. Blood samples were collected for hematological analysis, while skin samples were collected for microbiological, pathological, and immunohistochemical examinations. In addition, pathological examinations were performed on visceral organ samples. UV-C treatment caused rapid healing and complete or significant disinfection of skin lesions. Moreover, UV-C treatment reduced caspase-3 expressions in lesioned areas, according to immunochemistry. There were no pathological findings in visceral organs as a result of UV-C treatment. This study found that UV-C can be used to treat and disinfect infected skin lesions in short period and repeated doses.

Understanding the Role of Biofilms in Acute Recurrent Tonsillitis through 3D Bioprinting of a Novel Gelatin-PEGDA Hydrogel

Acute recurrent tonsillitis is a chronic, biofilm-related infection that is a significant burden to patients and healthcare systems. It is often treated with repeated courses of antibiotics, which contributes to antimicrobial resistance. Studying biofilms is key to understanding this disease. In vitro modelling using 3D bioprinted hydrogels is a promising approach to achieve this. A novel gelatin-PEGDA pseudomonas fluorescens-laden bioink was developed and bioprinted in a 3D hydrogel construct fabricated using computer-aided design to mimic the tonsillar biofilm environment. The bioprinted constructs were cultured at 37 °C in lysogeny broth for 12 days. Bacterial growth was assessed by spectrophotometry. Cellular viability analysis was conducted using optical fluorescence microscopy (FDA/PI staining). A biocompatible 3D-printed bacteria-laden hydrogel construct was successfully fabricated. Bacterial growth was observed using optical fluorescence microscopy. A live/dead cellular-staining protocol demonstrated bacterial viability. Results obtained after the 12-day culture period showed higher bacterial growth in the 1% gelatin concentration construct compared to the 0% control. This study demonstrates the first use of a bacteria-laden gelatin-PEGDA hydrogel for biofabrication of a 3D-printed construct designed to model acute recurrent tonsillitis. Initiating a study with clinically relevant ex vivo tonsil bacteria will be an important next step in improving treatment of this impactful but understudied disease.

Radical species generating technologies for decontamination of Listeria species in food: a recent review report

Foodborne illnesses occur due to the contamination of fresh, frozen, or processed food products by some pathogens. Among several pathogens responsible for the illnesses, Listeria monocytogenes is one of the lethal bacteria that endangers public health. Several preexisting and novel technologies, especially non-thermal technologies are being studied for their antimicrobial effects, particularly toward L. monocytogenes. Some noteworthy emerging technologies include ultraviolet (UV) or light-emitting diode (LED), pulsed light, cold plasma, and ozonation. These technologies are gaining popularity since no heat is employed and undesirable deterioration of food quality, especially texture, and taste is devoided. This review aims to summarize the most recent advances in non-thermal processing technologies and their effect on inactivating L. monocytogenes in food products and on sanitizing packaging materials. These technologies use varying mechanisms, such as photoinactivation, photosensitization, disruption of bacterial membrane and cytoplasm, etc. This review can help food processing industries select the appropriate processing techniques for optimal benefits, in which the structural integrity of food can be preserved while simultaneously destroying L. monocytogenes present in foods. To eliminate Listeria spp., different technologies possess varying mechanisms such as rupturing the cell wall, formation of pyrimidine dimers in the DNA through photochemical effect, excitation of endogenous porphyrins by photosensitizers, generating reactive species, causing leakage of cellular contents and oxidizing proteins and lipids. These technologies provide an alternative to heat-based sterilization technologies and further development is still required to minimize the drawbacks associated with some technologies.

RoboCoV Cleaner: An Indoor Autonomous UV-C Disinfection Robot with Advanced Dual-Safety Systems

In the face of today's ever-evolving global health landscape and ambient assisted living (AAL), marked by the persistent emergence of novel viruses and diseases that impact vulnerable categories and individual safety, the need for innovative disinfection solutions has surged to unprecedented levels. In pursuit of advancing the field of autonomous UV-C disinfection robotics, we conducted two comprehensive state-of-the-art analyses: the first one in the literature and the second one in existing commercial disinfection robots to identify current challenges. Of all of the challenges, we consider the most outstanding ones to be safeguarding humans and animals and understanding the surroundings while operating the disinfection process challenges that we will address in this article. While UV-C lamps have demonstrated their effectiveness in sterilizing air and surfaces, the field of autonomous UV-C disinfection robotics represents a critical domain that requires advancement, particularly in safeguarding the wellbeing of humans and animals during operation. Operating UV-C disinfection robots in close proximity to humans or animals introduces inherent risks, and existing disinfection robots often fall short in incorporating advanced safety systems. In response to these challenges, we propose the RoboCoV Cleaner-an indoor autonomous UV-C disinfection robot equipped with an advanced dual and redundant safety system. This novel approach incorporates multiple passive infrared (PIR) sensors and AI object detection on a 360-degree camera. Under our test, the dual-redundant system reached more than 90% when detecting humans with high accuracy using the AI system 99% up to 30 m away in a university hallway (different light conditions) combined with the PIR system (with lower accuracy). The PIR system was proved to be a redundant system for uninterrupted operation during communication challenges, ensuring continuous sensor information collection with a swift response time of 50 ms (image processing within 200 ms). It empowers the robot to detect and react to human presence, even under challenging conditions, such as when individuals wear masks, in complete darkness, under UV light, or in environments with blurred visual conditions. In our test, the detection system performed outstandingly well with up to 99% detection rate of humans. Beyond safety features, the RoboCoV Cleaner can identify objects in its surroundings. This capability empowers the robot to discern objects affected by UV-C light, enabling it to apply specialized rules for targeted disinfection. The proposed system exhibits a wide range of capabilities beyond its core purpose of disinfection, making it suitable for healthcare facilities, universities, conference venues, and hospitals. Its implementation has the ability to improve significantly human safety and protect people. By showcasing the RoboCoV Cleaner's safety-first approach and adaptability, we aim to set a new benchmark for UV-C disinfection robots, promoting clean and secure environments while protecting vulnerable people, even in challenging scenarios.

The Preclinical Validation of 405 nm Light Parasiticidal Efficacy on Leishmania donovani in Ex Vivo Platelets in a Rag2-/- Mouse Model

Violet-blue light of 405 nm in the visible spectrum at a dose of 270 J/cm2 alone has been shown to be an effective microbicidal tool for inactivating several bacteria, HIV-1, and Trypanosoma cruzi in ex vivo plasma and platelets. Unlike chemical- and ultraviolet (UV)-based pathogen inactivation methods for plasma and platelet safety, 405 nm light is shown to be less toxic to host cells at light doses that are microbicidal. In this report, we evaluated the parasiticidal activity of a 405 nm light treatment on platelets spiked with the Leishmania donovani parasite. Following the light treatment, parasite viability was observed to be near zero in both low- and high-titer-spiked platelets relative to controls. Furthermore, to test the residual infectivity after inactivation in vivo, the light-treated low-titer L. donovani-spiked platelets were evaluated in an immunodeficient Rag2-/- mouse model and monitored for 9 weeks. The parasiticidal efficacy of 405 nm light was evident from the lack of a presence of parasites in the mice spleens. Parasiticidal activity was confirmed to be mediated through 405 nm light-induced reactive oxygen species (ROS), as quantitatively measured by a 2',7'-Dichlorodihydrofluorescein diacetate (H2DCFDA)-based assay. Overall, these results confirm the complete inactivation of L. donovani spiked in ex vivo platelets by 405 nm light treatment and exemplify the utility of the Rag2-/- mouse infection model for the preclinical validation of the parasiticidal efficacy of 405 nm light and this light-based technology as a potential PRT for ex vivo platelets.

Photoinactivation of the bacteriophage PhiX174 by UVA radiation and visible light in SM buffer and DMEM-F12

OBJECTIVE

It has been observed that viruses can be inactivated by UVA radiation and visible light. The aim of this study is to investigate whether a medium that contains a photosensitizer might have an influence on viral reduction under irradiation by UVA, violet or blue light. Test virus is the bacteriophage PhiX174 in the photosensitizer-free SM buffer and DMEM-F12, which contains the known photosensitizer riboflavin.

RESULTS

The determined PhiX174 D90 doses in SM buffer and DMEM were 36.8 J/cm² and 13.6 J/cm² at 366 nm, 153.6 J/cm² and 129.1 J/cm² at 408 nm and 4988 J/cm² and 2477.1 J/cm² at 455 nm, respectively. It can be concluded that the medium has a large influence on the results. This might be caused by the photosensitizer riboflavin in DMEM-F12. As riboflavin is a key component in many cell culture media, irradiation experiments with viruses in cell culture media should be avoided if the investigation of intrinsical photoinactivation properties of viruses is aimed for.

Combined antibacterial effect of 460 nm light-emitting diode illumination and chitosan against Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes on fresh-cut melon, and the impact of combined treatment on fruit quality

This study evaluated the combined antibacterial effect of 460 nm LED illumination and chitosan on Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes on fresh-cut melon surface and its impact on the quality of melon at a total dose of 2.4 kJ/cm2 at 4 and 10 °C. Results showed that the antibacterial effect of LED illumination in combination with chitosan (0.5 and 1.0%) was much better than that of LED illumination alone, showing their synergistic effect. Among the pathogens, L. monocytogenes was the most susceptible pathogen to LED illumination. Although the color of melons became paler after LED illumination, there was little to no change in ascorbic acid content, total flavonoid content, or antioxidant capacity of the illuminated fruits compared with non-illuminated fruits. Thus, these results suggest that chitosan-mediated 460 nm LED illumination could be applied to inactivate foodborne pathogens on fresh-cut melons during storage at food establishments.

Could violet-blue lights increase the bacteria resistance against ultraviolet radiation mediated by photolyases?

Studies have demonstrated bacterial inactivation by radiations at wavelengths between 400 and 500 nm emitted by low-power light sources. The phototoxic activity of these radiations could occur by oxidative damage in DNA and membrane proteins/lipids. However, some cellular mechanisms can reverse these damages in DNA, allowing the maintenance of genetic stability. Photoreactivation is among such mechanisms able to repair DNA damages induced by ultraviolet radiation, ranging from ultraviolet A to blue radiations. In this review, studies on the effects of violet and blue lights emitted by low-power LEDs on bacteria were accessed by PubMed, and discussed the repair of ultraviolet-induced DNA damage by photoreactivation mechanisms. Data from such studies suggested bacterial inactivation after exposure to violet (405 nm) and blue (425-460 nm) radiations emitted from LEDs. However, other studies showed bacterial photoreactivation induced by radiations at 348-440 nm. This process occurs by photolyase enzymes, which absorb photons at wavelengths and repair DNA damage. Although authors have reported bacterial inactivation after exposure to violet and blue radiations emitted from LEDs, pre-exposure to such radiations at low fluences could activate the photolyases, increasing resistance to DNA damage induced by ultraviolet radiation.

Viricidal Efficacy of a 405-nm Environmental Decontamination System for Inactivation of Bacteriophage Phi6: Surrogate for SARS-CoV-2

The highly transmittable nature of SARS-CoV-2 has increased the necessity for novel strategies to safely decontaminate public areas. This study investigates the efficacy of a low irradiance 405-nm light environmental decontamination system for the inactivation of bacteriophage phi6 as a surrogate for SARS-CoV-2. Bacteriophage phi6 was exposed to increasing doses of low irradiance (~0.5 mW cm-2 ) 405-nm light while suspended in SM buffer and artificial human saliva at low (~103-4  PFU mL-1 ) and high (~107-8  PFU mL-1 ) seeding densities, to determine system efficacy for SARS-CoV-2 inactivation and establish the influence of biologically relevant suspension media on viral susceptibility. Complete/near-complete (≥99.4%) inactivation was demonstrated in all cases, with significantly enhanced reductions observed in biologically relevant media (P < 0.05). Doses of 43.2 and 172.8 J cm-2 were required to achieve ~3 log10 reductions at low density, and 97.2 and 259.2 J cm-2 achieved ~6 log10 reductions at high density, in saliva and SM buffer, respectively: 2.6-4 times less dose was required when suspended in saliva compared to SM buffer. Comparative exposure to higher irradiance (~50 mW cm-2 ) 405-nm light indicated that, on a per unit dose basis, 0.5 mW cm-2 treatments were capable of achieving up to 5.8 greater log10 reductions with up to 28-fold greater germicidal efficiency than that of 50 mW cm-2 treatments. These findings establish the efficacy of low irradiance 405-nm light systems for inactivation of a SARS-CoV-2 surrogate and demonstrate the significant enhancement in susceptibility when suspended in saliva, which is a major vector in COVID-19 transmission.

Synergistic effects of sequential light treatment with 222-nm/405-nm and 280-nm/405-nm wavelengths on inactivation of foodborne pathogens

Light-based technologies of different wavelengths can inactivate pathogenic microorganisms, but each wavelength has its limitations. This work explores the potential of sequential treatments with different wavelengths for enhancing the disinfection performance of individual treatments by employing various bactericidal mechanisms. The effectiveness, inactivation kinetics, and bactericidal mechanisms of treatments with 222/405, 280/405, and 405 nm alone against Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, Salmonella Typhimurium, and Pseudomonas aeruginosa were evaluated. Inactivation experiments were performed in thin liquid bacterial suspensions that were treated either individually with 48 h of 405-nm light or sequentially with (i) 30 s of 222-nm far-UV-C light, followed by 48 h of 405-nm light, or (ii) 30 s of 280-nm far-UV-C light, followed by 48 h of 405-nm light. Survivors were recovered and enumerated by standard plate counting. All inactivation curves were non-linear and followed the Weibull model (0.99 ≥ R2 ≥ 0.70). Synergistic effects were found for E. coli, L. monocytogenes, and S. Typhimurium, with maximum inactivation level increases of 2.9, 3.3, and 1.1 log CFU after the sequential treatments, respectively. Marginal synergy was found for S. aureus, and an antagonistic effect was found for P. aeruginosa after sequential treatments. Significant differences in reactive oxygen species accumulation were found (P < 0.05) after various treatment combinations, and the performance of sequential treatments was correlated with cellular oxidative damage. The sequential wavelength treatments proposed demonstrate the potential for enhanced disinfection of multiple foodborne pathogens compared with individual wavelength treatments, which can have significant food safety benefits. IMPORTANCE Nonthermal light-based technologies offer a chemical-free method to mitigate microbial contamination in the food and healthcare industries. However, each individual wavelength has different limitations in terms of efficacy and operating conditions, which limits their practical applicability. In this study, bactericidal synergism of sequential treatments with different wavelengths was identified. Pre-treatments with 280 and 222 nm enhanced the disinfection performance of follow-up 405-nm treatments for multiple foodborne pathogens by inducing higher levels of cellular membrane damage and oxidative stress. These findings deliver useful information for light equipment manufacturers, food processors, and healthcare users, who can design and optimize effective light-based systems to realize the full potential of germicidal light technologies. The results from the sequential treatments offer practical solutions to improve the germicidal efficacy of visible light systems, as well as provide inspiration for future hurdle disinfection systems design, with a positive impact on food safety and public health.

Curcumin and carvacrol mediated photodynamic inactivation with 405 nm light emitting diodes (LEDs) on Salmonella Enteritidis

Photodynamic inactivation (PDI) has a potential application for food preservation that can minimize food pathogens posing risks to consumer health. This study aimed to evaluate the antibacterial activity of 405 nm light-emitting diodes (LEDs) illumination in the presence of carvacrol and curcumin against Salmonella Enteritidis and S. Enteritidis PT4 at different temperatures (4 °C, 25 °C and 37 °C) and time parameters (15 min, 30 min and 45 min) in the illumination system. Compared to their individual treatment, the decrease in the bacterial population was stronger in bacteria treated with LEDs + carvacrol or LEDs + curcumin. Co-application of carvacrol or curcumin with LEDs at 37 °C showed strong antibacterial activity against both bacteria depending on the application time. Co-application at 37 °C for 45 min completely inhibited the growth of S. Enteritidis. LEDs, curcumin, carvacrol applications alone or LEDs + curcumin, LEDs + carvacrol applications caused a decrease in bacterial population in proportion to the increase in the storage temperature and application times. These results showed that carvacrol or curcumin potentiates LEDs illumination therapy against both bacteria. Future studies on adapting the PDI system to control bacteria in a variety of foods may help develop novel strategies to fight against foodborne bacterial pathogens.

Antibiotic resistances from slaughterhouse effluents and enhanced antimicrobial blue light technology for wastewater decontamionation

The frequencies of 6 different facultative pathogenic bacteria of the ESKAPE group (priority list WHO) and a total of 14 antibiotic resistance genes (ARGs) with different priorities for human medicine were quantified in wastewaters of poultry and pig slaughterhouses using molecular biological approaches. Raw sewage from poultry and pig slaughterhouses was found to be contaminated not only with facultative pathogenic bacteria but also with various categories of clinically relevant ARGs, including ARGs against the reserve antibiotics group. The concentration of the different gene targets decreased after on-site conventional biological or advanced oxidative wastewater treatments, but was not eliminated. Hence, the antimicrobial BlueLight (aBL) in combination with a porphyrin photo-sensitizer was studied with ESKAPE bacteria and real slaughterhouse wastewaters. The applied broad LED-based blue light (420-480 nm) resulted in groups of sensitive, intermediate, and non-sensitive ESKAPE bacteria. The killing effect of aBL was increased in the non-sensitive bacteria Klebsiella pneumoniae and Enterococcus faecium due to the addition of porphyrins in concentrations of 10-6 M. Diluted slaughterhouse raw wastewater was treated with broad spectrum aBL and in combination with porphyrin. Here, the presence of the photo-sensitizer enhanced the aBL biocidal impact.

Riboflavin and Its Derivates as Potential Photosensitizers in the Photodynamic Treatment of Skin Cancers

Riboflavin, a water-soluble vitamin B2, possesses unique biological and physicochemical properties. Its photosensitizing properties make it suitable for various biological applications, such as pathogen inactivation and photodynamic therapy. However, the effectiveness of riboflavin as a photosensitizer is hindered by its degradation upon exposure to light. The review aims to highlight the significance of riboflavin and its derivatives as potential photosensitizers for use in photodynamic therapy. Additionally, a concise overview of photodynamic therapy and utilization of blue light in dermatology is provided, as well as the photochemistry and photobiophysics of riboflavin and its derivatives. Particular emphasis is given to the latest findings on the use of acetylated 3-methyltetraacetyl-riboflavin derivative (3MeTARF) in photodynamic therapy.

Blue 405 nm LED light effectively inactivates bacterial pathogens on substrates and packaging materials used in food processing

This study investigates the antimicrobial effectiveness of 405 nm light emitting diodes (LEDs) against pathogenic Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, and Staphylococcus aureus, in thin liquid films (TLF) and on solid surfaces. Stainless steel (SS), high density polyethylene (HDPE), low density polyethylene (LDPE), and borosilicate glass were used as materials typically encountered in food processing, food service, and clinical environments. Anodic aluminum oxide (AAO) coupons with nanoscale topography were used, to evaluate the effect of topography on inactivation. The impact of surface roughness, hydrophobicity, and reflectivity on inactivation was assessed. A 48 h exposure to 405 nm led to reductions ranging from 1.3 (E. coli) to 5.7 (S. aureus) log CFU in TLF and 3.1 to 6.3 log CFU on different solid contact surfaces and packaging materials. All inactivation curves were nonlinear and followed Weibull kinetics, with better inactivation predictions on surfaces (0.89 ≤ R2 ≤ 1.0) compared to TLF (0.76 ≤ R2 ≤ 0.99). The fastest inactivation rate was observed on small nanopore AAO coupons inoculated with L. monocytogenes and S. aureus, indicating inactivation enhancing potential of these surfaces. These results demonstrate significant promise of 405 nm LEDs for antimicrobial applications in food processing and handling and the healthcare industry.

An Approach to Improve Energy Efficiency during Antimicrobial Blue Light Inactivation: Application of Pulse-Width Modulation Dimming to Balance Irradiance and Irradiation Time

Antimicrobial blue light (aBL) is an effective non-destructive inactivation technique and has received increasing attention. Despite its significance, the existing research has not thoroughly delved into the impacts of irradiance and irradiation time on enhancing energy efficiency during aBL inactivation and the explanation of the enhancement effect of pulse exposure. In this paper, a series of Escherichia coli inactivation experiments with different duty cycles, pulse frequencies, and irradiation times were conducted, and the relative concentrations of reactive oxygen species (ROS) were measured under corresponding conditions. A two-dimensional (2-D) Hom model was proposed to evaluate the effect of irradiance and irradiation time. The results show that, compared to continuous exposure, pulsed aBL (duty cycle = 25%) can save ~37% of the energy to achieve the same inactivation effect and generate a 1.95 times higher ROS concentration. The 2-D Hom model obtains the optimal combination of average irradiance and time according to the desired reduction and shows that the irradiation time has a higher weight than the irradiance (1.677 and 1.083, respectively). Therefore, using pulse exposure with a lower average irradiance for a longer period of time can achieve a better inactivation effect when consuming equivalent energy. The proposed pulse-width modulation dimming approach helps promote the application of the aBL technique.

Light tolerance of extended spectrum β-lactamase producing Escherichia coli strains after repetitive exposure to far-UVC and blue LED light

AIMS

The aim of this study was to investigate dual far-UVC (Ultraviolet-C) (222 nm) and blue LED (Light Emitting Diode) (405 nm) light on the inactivation of extended spectrum β-lactamase-producing Escherichia coli (ESBL-Ec) and to determine if repetitive exposure to long pulses of light resulted in changes to light tolerance, and antibiotic susceptibility.

METHODS AND RESULTS

Antimicrobial efficiency of dual and individual light wavelengths and development of light tolerance in E. coli was evaluated through a spread plate method after exposure to light at 25 cm. Dual light exposure for 30 min resulted in a 5-6 log10 CFU mL-1 reduction in two ESBL-Ec and two antibiotic-sensitive control E. coli strains. The overall inhibition achieved by dual light treatment was always greater than the combined reductions (log10 CFU) observed from exposure to individual light wavelengths (combined 222-405 nm), indicating a synergistic relationship between blue LED and far-UVC light when used together. Repetitive long pulses of dual and individual far-UVC light exposure resulted in light tolerance in two ESBL-Ec strains but not the antibiotic-sensitive E. coli strains. Subsequent passages of repetitive light-treated ESBL-Ec strains continued to exhibit light tolerance. Antibiotic susceptibility was determined through a standard disk diffusion method. No changes were observed in the antibiotic susceptibility profiles for any of the four strains after exposure to either dual or individual wavelengths.

CONCLUSIONS

Dual light exposure was effective in the disinfection of ESBL-Ec in solution; however, antibiotic-resistant E. coli were able to develop light tolerance after repetitive exposure to light.

Laboratory evaluation of the broad-spectrum antibacterial efficacy of a low-irradiance visible 405-nm light system for surface-simulated decontamination

Purpose

Lighting systems which use visible light blended with antimicrobial 405-nm violet-blue light have recently been developed for safe continuous decontamination of occupied healthcare environments. This paper characterises the optical output and antibacterial efficacy of a low irradiance 405-nm light system designed for environmental decontamination applications, under controlled laboratory conditions.

Methods

In the current study, the irradiance output of a ceiling-mounted 405-nm light source was profiled within a 3×3×2 m (18 m3) test area; with values ranging from 0.001-2.016 mWcm-2. To evaluate antibacterial efficacy of the light source for environmental surface decontamination, irradiance levels within this range (0.021-1 mWcm-2) at various angular (Δ ϴ=0-51.3) and linear (∆s=1.6-2.56 m) displacements from the source were used to generate inactivation kinetics, using the model organism, Staphylococcus aureus. Additionally, twelve bacterial species were surface-seeded and light-exposed at a fixed displacement below the source (1.5 m; 0.5 mWcm-2) to demonstrate broad-spectrum efficacy at heights typical of high touch surfaces within occupied settings.

Results

Results demonstrate that significant (P≤0.05) inactivation was successfully achieved at all irradiance values investigated, with spatial positioning from the source affecting inactivation, with greater times required for inactivation as irradiance decreased. Complete/near-complete (≥93.28%) inactivation of all bacteria was achieved following exposure to 0.5 mWcm-2 within exposure times realistic of those utilised practically for whole-room decontamination (2-16 h).

Conclusion

This study provides fundamental evidence of the efficacy, and energy efficiency, of low irradiance 405-nm light for bacterial inactivation within a controlled laboratory setting, further justifying its benefits for practical infection control applications.

Current decontamination challenges and potentially complementary solutions to safeguard the vulnerable seafood industry from recalcitrant human norovirus in live shellfish: Quo Vadis?

Safeguarding the seafood industry is important given its contribution to supporting our growing global population. However, shellfish are filter feeders that bioaccumulate microbial contaminants in their tissue from wastewater discharged into the same coastal growing environments leading to significant human disease outbreaks unless appropriately mitigated. Removal or inactivation of enteric viruses is very challenging particularly as human norovirus (hNoV) binds to specific histo-blood ligands in live oyster tissue that are consumed raw or lightly cooked. The regulatory framework that sets out use of clean seawater and UV disinfection is appropriate for bacterial decontamination at the post-harvest land-based depuration (cleaning) stage. However, additional non-thermal technologies are required to eliminate hNoV in live shellfish (particularly oysters) where published genomic studies report that low-pressure UV has limited effectiveness in inactivating hNoV. The use of the standard genomic detection method (ISO 15, 216-1:2017) is not appropriate for assessing the loss of infectious hNoV in treated live shellfish. The use of surrogate viral infectivity methods appear to offer some insight into the loss of hNoV infectiousness in live shellfish during decontamination. This paper reviews the use of existing and potentially other combinational treatment approaches to enhance the removal or inactivation of enteric viruses in live shellfish. The use of alternative and complementary novel diagnostic approaches to discern viable hNoV are discussed. The effectiveness and virological safety of new affordable hNoV intervention(s) require testing and validating at commercial shellfish production in conjunction with laboratory-based research. Appropriate risk management planning should encompass key stakeholders including local government and the wastewater industry. Gaining a mechanistic understanding of the relationship between hNoV response at molecular and structural levels in individually treated oysters as a unit will inform predictive modeling and appropriate treatment technologies. Global warming of coastal growing environments may introduce additional contaminant challenges (such as invasive species); thus, underscoring need to develop real-time ecosystem monitoring of growing environments to alert shellfish producers to appropriately mitigate these threats.

Ultrasound-assisted blue light killing Vibrio parahaemolyticus to improve salmon preservation

Vibrio parahaemolyticus is a typical marine bacterium, which often contaminates seafood and poses a health risk to consumers. Some non-thermal sterilization technologies, such as ultrasonic field (UF) and blue light (BL) irradiation, have been widely used in clinical practice due to their efficiency, safety, and avoidance of drug resistance, but their application in food preservation has not been extensively studied. This study aims to investigate the effect of BL on V. parahaemolyticus in culture media and in ready-to-eat fresh salmon, and to evaluate the killing effectiveness of the UF combined with BL treatment on V. parahaemolyticus. The results showed that BL irradiation at 216 J/cm2 was effective in causing cell death (close to 100%), cell shrinkage and reactive oxygen species (ROS) burst in V. parahaemolyticus. Application of imidazole (IMZ), an inhibitor of ROS generation, attenuated the cell death induced by BL, indicating that ROS were involved in the bactericidal effects of BL on V. parahaemolyticus. Furthermore, UF for 15 min enhanced the bactericidal effect of BL at 216 J/cm2 on V. parahaemolyticus, with the bactericidal rate of 98.81%. In addition, BL sterilization did not affect the color and quality of salmon, and the additive UF treatment for 15 min did not significant impact on the color of salmon. These results suggest that BL or UF combined with BL treatment has potential for salmon preservation, however, it is crucial to strictly control the intensity of BL and the duration of UF treatment to prevent reducing the freshness and brightness of salmon.

The Parameters Affecting Antimicrobial Efficiency of Antimicrobial Blue Light Therapy: A Review and Prospect

Antimicrobial blue light (aBL) therapy is a novel non-antibiotic antimicrobial approach which works by generating reactive oxygen species. It has shown excellent antimicrobial ability to various microbial pathogens in many studies. However, due to the variability of aBL parameters (e.g., wavelength, dose), there are differences in the antimicrobial effect across different studies, which makes it difficult to form treatment plans for clinical and industrial application. In this review, we summarize research on aBL from the last six years to provide suggestions for clinical and industrial settings. Furthermore, we discuss the damage mechanism and protection mechanism of aBL therapy, and provide a prospect about valuable research fields related to aBL therapy.

Genome-wide transcriptional response of Escherichia coli O157:H7 to light-emitting diodes with various wavelengths

We investigated the physiological and transcriptomic response of Escherichia coli at the early stationary phase to light-emitting diodes with different wavelengths. The growth and metabolic changes of E. coli O157:H7 were examined under the influence of 465, 520, and 625 nm illuminated light. Under 465 nm illumination, the growth of E. coli O157:H7 was significantly retarded compared to 520 nm and 625 nm illumination and non-illuminated control. Metabolic changes were examined under these illumination and non-illuminated conditions based on transcriptomic reads. Transcriptomic response under 520 nm and 625 nm remained almost similar to control except few up-and down-regulated genes. Carbohydrates metabolic transcriptomic reads were greatly down-regulated under 465 nm illumination compared to 520 nm and 625 nm illumination and non-illuminated control showing depletion of glucose as a sole energy source during the exponential phase. Fatty acid degradation such as fad regulon-related genes was up-regulated in cells under 465 nm illumination revealing the shifting of cells to use fatty acid as a new carbon energy source during the early stationary phase. Exposure of E. coli O157:H7 cells to 465 nm illuminated light down-regulated virulence factor genes such as hlyA, hlyB, hlyC, stx1A, stx2B, paa, and bdm. Under the stress of 465 nm illumination, expression of stress and flagellar motility-related genes were up-regulated causing consumption of energy and reduction in cell growth. Also, oxidative phosphorylated transcriptomic reads were up-regulated under 465 nm illumination probably due to the production of ROS that might involve in the reduction of cell growth during the early stationary phase. These results indicate that pathogenic E. coli O157:H7 respond differentially to a different wavelength of the light-emitting diodes used in this study.

Chitosan enhances antibacterial efficacy of 405 nm light-emitting diode illumination against Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. on fresh-cut melon

This study aimed to evaluate the influence of chitosan on the antibacterial efficacy of 405 nm LED illumination against Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes on fresh-cut melons. The antibacterial efficacy of LED illumination (a total dose of 1.3 kJ/cm²) with or without chitosan (0.5 and 1.0 %) against these three pathogens was determined at 4 and 10 °C, respectively. Non-illuminated and chitosan-treated fruits were stored in the dark for 36 h under the same temperature. Color changes, ascorbic acid content, and total flavonoid content of illuminated and non-illuminated fruits were also analyzed. The results showed that the populations of all three pathogens on the non-illuminated and chitosan-treated fruits remained unchanged during storage. Regardless of bacterial species and chitosan concentrations, LED illumination in combination with chitosan greatly reduced the bacterial populations by 1.5 - 3.5 log/cm², which was greater than LED illumination alone. Among the three pathogens, L. monocytogenes was the most susceptible to chitosan-mediated LED illumination. However, the whiteness index of illuminated fruits significantly increased by 1.3-fold compared to that of non-illuminated fruits, regardless of the presence of chitosan. Unlike color, no significant difference was observed in ascorbic acid and total flavonoid contents between illuminated and non-illuminated fruits. Although the fruit color was changed by LED illumination, these results indicate that adding chitosan could enhance the antibacterial efficacy of 405 nm LED illumination against major foodborne pathogens on fresh-cut melons without changing nutritional quality.

A singlet state oxygen generation model based on the Monte Carlo method of visible antibacterial blue light inactivation

Visible antibacterial blue light (VABL) has received much attention recently as a nondestructive inactivation approach. However, due to the sparse distribution of bacteria, the light energy evaluation method used in existing studies is inaccurate. Thus, the sensitivity of microorganisms to VABL in different experiments cannot be compared. In this paper, a Monte Carlo-based photon transport model with the optimized scattering phase function was constructed. The model calculated the spatial light energy distribution and the temporal distribution of cumulative singlet state oxygen (CSO) under various cell and medium parameters. The simulation results show that when the cells are sparsely distributed, <30% of light energy from the light source is absorbed by microbes and participates in photochemical reactions. The CSO produced increases with cell density and cell size. Little light energy is available, and thus, the concentration of CSO produced is insufficient to inactivate microbes at deeper depths. As the light intensity and inactivation time increased, the production of singlet state oxygen tended to level off. The model proposed here can quantify the generation of singlet state oxygen and provide a more accurate light energy guide for the VABL inactivation process.

Safer school with near-UV technology: novel applications for environmental hygiene

Systems capable of disinfecting air and surfaces could reduce the risk of infectious diseases transmission. Aim: to evaluate the effectiveness of near-UV LED ceiling lamps, with a wavelength of 405 nm, in improving environmental hygiene. Between November and December 2020, we conducted an experimental study having a pre-post design in a kindergarten room in Siena where 4 ceiling lamps with 405 nm LED technology were installed. Twice per day, sampling was performed before (T0) and after treatment with near-UV (T1). We used between 8 and 12 pairs of contact plates to sample at various random spots each day. Air samplings were also performed. The plates were incubated at 22 and 36 °C. Significance was set at 95% (p < 0.05). The mean level of Colony Forming Unit (CFU) at T(0) was 249 (95% CI 193.1 - 305.0) at 36 °C and 535.2 (374.3 - 696.1) at 22 °C. The reduction was significant at T(1): by 65% at 36 °C and, 72% at 22 °C. Also, for air contamination: 95.3% (98.4-92.3). A dose threshold of about 5 J/cm² was identified to have an 80% CFU abatement and remains nearly constant. The advantage of being able to use this technology in the presence of people is very important in the context of controlling environmental contamination.

Graphical abstract

Strategic insight into enhanced photocatalytic remediation of pharmaceutical contaminants using spherical CdO nanoparticles in visible light region

The sustainable control of pharmaceutical micropollutants in water and wastewater environments is a great challenge in the 21st century. To address these issues, unique CdO nanoparticles (NPs) were synthesized using a facile hydrothermal approach and investigated for photocatalytic control of the antibiotic tetracycline, multidrug-resistant bacteria (MDRB), and total coliform in the wastewater effluent. The NPs were characterized using a range of techniques and it exhibited a spherical-like crystal structure with a mean size of 40 nm. The vibrational stretching mode of 1419 cm^-1 confirmed the formation of Cd-O (M - O). The synthesis protocol formed smoother surfaces and 1.88 eV band gap energy of CdO NPs, inducing excellent photocatalytic activity under visible LED light (blue and white) irradiation. The optimal catalyst dose and pH were 100 mg/L and 8-9, respectively. Blue light proved more effective than white light, resulting in 28% higher efficiency (93 ± 0.47%) in tetracycline degradation than white light under an identical intensity (20 mW/cm²). White light required a four-fold higher light intensity (80 mW/cm²) than blue light to induce comparable photocatalytic MDRB inactivation. Bacterial cell lysis by the photocatalytic treatment was confirmed by transmission electron microscopy (TEM). The used catalyst was easily recovered by 5 min of centrifugation and re-used without any noticeable change in the photocatalytic decomposition. The trapping experiment revealed that the CdO-based NPs contributed primarily to the generation of •O₂^- and •OH radicals (Type I), but the •O₂^- radicals were the dominant reactive oxygen species (ROS) in the photocatalytic process.

Antimicrobial Photodynamic Therapy as a Technique for Decontamination of Acrylic Resin Devices Provided by Different Dental Laboratories

Introduction: Dentures, occlusal splints, surgical guides and orthodontic appliances are examples of acrylic resin devices made in dental laboratories, which must be disinfected and even sterilized before insertion into the oral cavity. This study evaluated the antimicrobial effect of photodynamic therapy (PDT) applied to acrylic resin specimens received from different laboratories. Methods: Three hundred standardized specimens were ordered from six randomly selected laboratories registered in the Council of Dentistry of Ceará (n=50). The PDT consisted in the association of 22 µM erythrosine, as a photosensitizer (P), and a 520-nm LED at 38 J/cm² (L). The specimens of each laboratory were randomly distributed into five groups: positive control, sterilized with ethylene oxide; negative control, untreated (P-L-); erythrosine control, only stained (P+L-); LED control, only irradiated (P-L+); PDT (P+L+). Then, the specimens were individually sonicated in saline solution; the suspension was diluted, plated on culture mediums (blood agar, sabouraud dextrose agar and a non-selective chromogenic agar), and incubated for 48 hours at 37°C. Colony-forming-unit (CFU) counts were done and statistical tests of Kruskal-Wallis/Dunn were carried out. Results: The specimens from all laboratories were contaminated with bacteria and yeasts. Staphylococcus aureus, Staphylococcus saprophyticus, Escherichia coli, Enterococcus spp., Klebsiella and Pseudomonas spp. were identified. The PDT significantly reduced CFU counts (P<0.0001), compared to P-L-. Conclusion: PDT was able to effectively decontaminate the acrylic resin specimens provided from dental laboratories.

Effectiveness of curcumin-based antimicrobial photodynamic therapy against Staphylococcus aureus

PURPOSE

This study investigated the effectiveness of curcumin-based antimicrobial photodynamic therapy (aPDT) against Staphylococcus aureus (S. aureus), the causative agent of ventilator-associated pneumonia.

METHODS

Curcumin was added to S. aureus culture medium at concentrations of 25, 2.5, and 0.25 µM. After 60 min (20-25°C), each culture was irradiated for 1 and 3 min, and viable bacteria were counted. Curcumin (25 µM) was also added to a bacterial suspension with D-mannitol and sodium azide; microbial counts were determined after irradiation for 3 min.

RESULTS

S. aureus was significantly reduced in the 1-min (P = 0.043) and 3-min (P = 0.011) irradiation groups in comparison to the 0-min irradiation group with 25 µM curcumin. No significant differences were observed between the curcumin alone group and the curcumin plus D-mannitol or sodium azide group.

CONCLUSION

The findings of this study indicate that prolonged exposure (≥1 min) of S. aureus to LED in 25 μM curcumin solution induces cell wall injury. Curcumin-based aPDT as an adjunct to conventional oral care, employing existing dentistry equipment, offers a promising approach that does not rely on antimicrobial drugs or allows the emergence of resistant bacterial strains. This suggests its potential role in future strategies aimed at preventing ventilator-associated pneumonia.

Effectiveness of front line and emerging fungal disease prevention and control interventions and opportunities to address appropriate eco-sustainable solutions

Fungal pathogens contribute to significant disease burden globally; however, the fact that fungi are eukaryotes has greatly complicated their role in fungal-mediated infections and alleviation. Antifungal drugs are often toxic to host cells and there is increasing evidence of adaptive resistance in animals and humans. Existing fungal diagnostic and treatment regimens have limitations that has contributed to the alarming high mortality rates and prolonged morbidity seen in immunocompromised cohorts caused by opportunistic invasive infections as evidenced during HIV and COVID-19 pandemics. There is a need to develop real-time monitoring and diagnostic methods for fungal pathogens and to create a greater awareness as to the contribution of fungal pathogens in disease causation. Greater information is required on the appropriate selection and dose of antifungal drugs including factors governing resistance where there is commensurate need to discover more appropriate and effective solutions. Popular azole fungal drugs are widely detected in surface water and sediment due to incomplete removal in wastewater treatment plants where they are resistant to microbial degradation and may cause toxic effects on aquatic organisms such as algae and fish. UV has limited effectiveness in destruction of anti-fungal drugs where there is increased interest in the combination approaches such as novel use of pulsed-plasma gas-discharge technologies for environmental waste management. There is growing interest in developing alternative and complementary green eco-biocides and disinfection innovation. Fungi present challenges for cleaning, disinfection and sterilization of reusable medical devices such as endoscopes where they (example, Aspergillus and Candida species) can be protected when harboured in build-up biofilm from lethal processing. Information on the efficacy of established disinfection and sterilization technologies to address fungal pathogens including bottleneck areas that present high risk to patients is lacking. There is a need to address risk mitigation and modelling to inform efficacy of appropriate intervention technologies that must consider all contributing factors where there is potential to adopt digital technologies to enable real-time analysis of big data, such as use of artificial intelligence and machine learning. International consensus on standardised protocols for developing and reporting on appropriate alternative eco-solutions must be reached, particularly in order to address fungi with increasing drug resistance where research and innovation can be enabled using a One Health approach.

Efficacy of violet-blue light to inactive microbial growth

The increase in health care-associated infections and antibiotic resistance has led to a growing interest in the search for innovative technologies to solve these problems. In recent years, the interest of the scientific community has focused on violet-blue light at 405 nm (VBL405). This study aimed to assess the VBL405 efficiency in reducing microbial growth on surfaces and air. This descriptive study run between July and October 2020. Petri dishes were contaminated with P. aeruginosa, E. coli, S. aureus, S. typhimurium, K. pneumoniae and were placed at 2 and 3 m from a LED light source having a wavelength peak at 405 nm and an irradiance respectively of 967 and 497 µW/cm². Simultaneously, the air in the room was sampled for 5 days with two air samplers (SAS) before and after the exposition to the VBL405 source. The highest microbial reduction was reached 2 m directly under the light source: S. typhimurium (2.93 log₁₀), K. pneumoniae (2.30 log₁₀), S. aureus (3.98 log₁₀), E. coli (3.83 log₁₀), P. aeruginosa (3.86 log₁₀). At a distance of 3 m from the light source, the greatest reduction was observed for S. aureus (3.49 log₁₀), and P. aeruginosa (3.80 log₁₀). An average percent microbial reduction of about 70% was found in the sampled air after 12 h of exposure to VBL405. VBL405 has proven to contrast microbial growth on the plates. Implementing this technology in the environment to provide continuous disinfection and to control microbial presence, even in the presence of people, may be an innovative solution.

Specular Reflection Suppression through the Adjustment of Linear Polarization for Tumor Diagnosis Using Fluorescein Sodium

In tumor surgery, the edges of the tumor can be visually observed using a fluorescent contrast agent and a fluorescent imaging device. By distinguishing it from normal tissues and blood vessels, it is possible to objectively judge the extent of resection while visually observing it during surgery, and it guarantees safe tumor resection based on more information. However, the main problem of such an imaging device is the specular reflection phenomenon. If specular reflection overlaps with important lesion locations, they are a major factor leading to diagnostic errors. Here, we propose a method to reduce specular reflection that occurs during tumor diagnosis using a linear polarization filter and fluorescent contrast agent. To confirm the effect of removing specular reflection, a self-made fluorescein sodium vial phantom was used, and the reliability of the results was increased using a large animal (pig) test. As a result of the experiment, it was possible to obtain an image in which specular reflection was removed by controlling the rotation angle of the filter by 90° and 270°, and the same results were confirmed in the phantom experiment and the animal experiment.

The Wavelength-Based Inactivation Effects of a Light-Emitting Diode Module on Indoor Microorganisms

With the increased incidence of infectious disease outbreaks in recent years such as the COVID-19 pandemic, related research is being conducted on the need to prevent their spread; it is also necessary to develop more general physical-chemical control methods to manage them. Consequently, research has been carried out on light-emitting diodes (LEDs) as an effective means of light sterilization. In this study, the sterilization effects on four types of representative bacteria and mold that occur indoors, Bacillus subtilis, Escherichia coli, Penicillium chrysogenum, and Cladosporium cladosporidides, were confirmed using LED modules (with wavelengths of 275, 370, 385, and 405 nm). Additionally, power consumption was compared by calculating the time required for 99.9% sterilization of each microorganism. The results showed that the sterilization effect was high, in the order 275, 370, 385, and 405 nm. The sterilization effects at 385 and 405 nm were observed to be similar. Furthermore, when comparing the power consumption required for 99.9% sterilization of each microorganism, the 275 nm LED module required significantly less power than those of other wavelengths. However, at 405 nm, the power consumption required for 99.9% sterilization was less than that at 370 nm; that is, it was more efficient and similar to or less than that at 385 nm. Additionally, because 405 nm can be applied as general lighting, it was considered to have wider applicability and utility compared with UV wavelengths. Consequently, it should be possible to respond to infectious diseases in the environment using LEDs with visible light wavelengths.

Efficacy of 405 nm Light-Emitting Diode Illumination and Citral Used Alone and in Combination for Inactivation of Vibrio parahaemolyticus on Shrimp

Vibrio parahaemolyticus is a widely distributed pathogen, which is frequently the lead cause of infections related to seafood consumption. The objective of the present study was to investigate the antimicrobial effect of the combination of 405 nm light-emitting diode (LED) and citral on V. parahaemolyticus. The antimicrobial effect of LED illumination and citral was evaluated on V. parahaemolyticus not only in phosphate-buffered saline (PBS) but also on shrimp. Quality changes of shrimp were determined by sensory evaluation. Changes in bacteria cell membrane morphology, cell membrane permeability, cell lipid oxidation level, and DNA degradation were examined to provide insights into the antimicrobial mechanism. The combination of LED treatments and citral had better antimicrobial effects than either treatment alone. LED combined with 0.1 mg/mL of citral effectively reduced V. parahaemolyticus from 6.5 log CFU/mL to below the detection limit in PBS. Combined treatment caused a 3.5 log reduction of the pathogen on shrimp within 20 min and a 6 log reduction within 2 h without significant changes in the sensory score. Furthermore, combined LED and citral treatment affected V. parahaemolyticus cellular morphology and outer membrane integrity. The profile of the comet assay and DNA fragmentation analysis revealed that combination treatment did not cause a breakdown of bacterial genomic DNA. In conclusion, LED may act synergistically with citral. They have the potential to be developed as novel microbial intervention strategies.

The effect of indoor daylight spectrum and intensity on viability of indoor pathogens on different surface materials

Built environments play a key role in the transmission of infectious diseases. Ventilation rates, air temperature, and humidity affect airborne transmission while cleaning protocols, material properties and light exposure can influence viability of pathogens on surfaces. We investigated how indoor daylight intensity and spectrum through electrochromic (EC) windows can impact the growth rate and viability of indoor pathogens on different surface materials (polyvinyl chloride [PVC] fabric, polystyrene, and glass) compared to traditional blinds. Results showed that tinted EC windows let in higher energy, shorter wavelength daylight than those with clear window and blind. The growth rates of pathogenic bacteria and fungi were significantly lower in spaces with EC windows compared to blinds: nearly 100% growth rate reduction was observed when EC windows were in their clear state followed by 41%-100% reduction in bacterial growth rate and 26%-42% reduction in fungal growth rate when EC windows were in their darkest tint. Moreover, bacterial viabilities were significantly lower on PVC fabric when they were exposed to indoor light at EC-tinted window. These findings are deemed fundamental to the design of healthy modern buildings, especially those that encompass sick and vulnerable individuals.

Photoinactivation of Salmonella enterica exposed to 5-aminolevulinic acid: Impact of sensitization conditions and irradiation time

The photodynamic inactivation (PDI) represents the potential alternative to traditional antibiotic therapy, and can be applied to treat various bacterial infections, including those caused by Gram-negative bacterial strains. One of the treatment modalities is based on the capacity of bacterial cells to synthesize the excess amounts of porphyrins after exposure to an externally applied 5-aminolevulinic acid (5-ALA), which makes them photosensitive and leads to reduced survival after irradiation with an appropriately selected light source. This study focuses on the sensitization and the photoinduced inactivation of Salmonella enterica cells in PBS containing 0.5 mM 5-ALA, incubated at 37 °C for 4 h or for 20 h and afterwards irradiated with violet LED light (11.1 mW/cm², a peak at 400 nm). It has been found that both amounts and composition of endogenous porphyrins not only depended on the incubation duration, but also were affected by externally induced photo- and chemo-oxidation reactions. The application of different sensitization conditions has revealed that the increasing amounts of endogenously produced porphyrins do not ensure the proportional reduction of bacterial cell survival numbers. The comparative investigations also demonstrated that the presence of endogenously produced porphyrins in the medium results in secondary sensitization of bacterial cells and causes a notably stronger photoinactivation effect in comparison to their externally applied standards.

Inactivation of Shigella flexneri by 405-nm Light-Emitting Diode Treatment and Possible Mechanism of Action

Shigella flexneri, a common Gram-negative foodborne pathogen, is widely distributed in fresh-cut fruits and vegetables, unpasteurized milk, and food processing environments. The aims of this study were to evaluate the antibacterial effects of 405-nm light-emitting diode (LED) treatment on S. flexneri and to investigate the possible mechanism. The results showed that LED irradiation (360 min) reduced the number of S. flexneri in phosphate-buffered saline by 3.29 log colony-forming unit (CFU)/mL (initial bacterial count: 6.81 log CFU/mL). The cells in reconstituted infant formula, cells on fresh-cut carrot slices, and biofilm-associated cells on stainless steel surfaces were reduced by 1.83 log CFU/mL, 7.00 log CFU/cm², and 4.35 log CFU/cm² following LED treatment for 360, 120, and 120 min, respectively. LED treatment damaged both DNA and cell wall of S. flexneri and changed cell morphology and cell membrane permeability. In addition, LED treatment decreased total cell protein concentration of S. flexneri. These results indicated that 405-nm LED treatment effectively controlled S. flexneri contamination of foods and food contact surfaces and that the bacterial inactivation may be the result of damage to multiple cellular components. These findings highlight the potential of LED technology in controlling S. flexneri during food processing, storage, and preparation.