Inactivation of Escherichia coli , Listeria and Salmonella by single and multiple wavelength ultraviolet-light emitting diodes

Cell density and extracellular matrix composition mitigate bacterial biofilm sensitivity to UV-C LED irradiation

Ultraviolet-C light-emitting diodes (UV-C LEDs) are an emerging technology for decontamination applications in different sectors. In this study, the inactivation of bacterial biofilms was investigated by applying an UV-C LED emitting at 280 nm and by measuring both the influence of the initial cell density (load) and presence of an extracellular matrix (biofilm). Two bacterial strains exposing diverging matrix structures and biochemical compositions were used: Pseudomonas aeruginosa and Leuconostoc citreum. UV-C LED irradiation was applied at three UV doses (171 to 684 mJ/cm2) on both surface-spread cells and on 24-h biofilms and under controlled cell loads, and bacterial survival was determined. All surface-spread bacteria, between 105 and 109 CFU/cm2, and biofilms at 108 CFU/cm2 showed that bacterial response to irradiation was dose-dependent. The treatment efficacy decreased significantly for L. citreum surface-spread cells when the initial cell load was high, while no load effect was observed for P. aeruginosa. Inactivation was also reduced when bacteria were grown under a biofilm form, especially for P. aeruginosa: a protective effect could be attributed to abundant extracellular DNA and proteins in the matrix of P. aeruginosa biofilms, as revealed by Confocal Laser Scanning Microscopy observations. This study showed that initial cell load and exopolymeric substances are major factors influencing UV-C LED antibiofilm treatment efficacy. KEY POINTS: • Bacterial cell load (CFU/cm2) could impact UV-C LED irradiation efficiency • Characteristics of the biofilm matrix have a paramount importance on inactivation • The dose to be applied can be predicted based on biofilm properties.

Effect of Optimized UV-LED Technology on Modeling, Inactivation Kinetics and Microbiological Safety in Tomato Juice

This research analyzed, optimized and modeled the inactivation kinetics of pathogenic bacteria (PB1: Escherichia coli O157:H7 and PB2: Listeria monocytogenes) and determined the microbiological safety of tomato juice processed by UV-LED irradiation and heat treatment. UV-LED processing conditions were optimized using response surface methodology (RSM) and were 90% power intensity, 21 min and 273-275 nm (251 mJ/cm2) with R2 > 0.96. Using the optimal conditions, levels of PB1 and PB2 resulted a log reduction of 2.89 and 2.74 CFU/mL, respectively. The Weibull model was efficient for estimating the log inactivation of PB1 and PB2 (CFU/mL). The kinetic parameter δ showed that 465.2 mJ/cm2 is needed to achieve a 90% log (CFU/mL) reduction in PB1 and 511.3 mJ/cm2 for PB2. With respect to the scale parameter p > 1, there is a descending concave curve. UV-LED-treated tomato juice had an 11.4% lower Listeria monocytogenes count than heat-treated juice on day 28 (4.0 ± 0.82 °C). Therefore, UV-LED technology could be used to inactivate Escherichia coli O157:H7 and Listeria monocytogenes, preserving tomato juice for microbiological safety, but studies are required to further improve the inactivation of these pathogens and analyze other fruit and vegetable juices.

Inactivation of pathogenic microorganisms in water by electron beam excitation multi-wavelength ultraviolet irradiation: Efficiency, influence factors and mechanism

Due to the limitations of traditional ultraviolet (UV) in microbial inactivation in water, it is necessary to explore a more suitable and efficient UV disinfection method. In this study, an electron beam excitation multi-wavelength ultraviolet (EBE-MW-UV) system was established and aims to analyze its differential microbial inactivation capabilities in comparison to single-wavelength UV-LEDs in waterborne applications. Furthermore, the inactivation mechanisms of this system on microorganisms were explored. The results showed that EBE-MW-UV had significantly higher inactivation effects on the Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Candida albicans in water compared to UV-LEDs (p＜0.05), and the inactivation effect of EBE-MW-UV on Escherichia coli and Pseudomonas aeruginosa at the same UV dose was 3.8 and 1.9 log higher than that of UV-LEDs, respectively, EBE-MW-UV exhibited better inactivation effects on Gram-negative bacteria. Further research found that, under the majority of irradiation doses, neither EBE-MW-UV nor UV-LEDs were significantly affected by the concentration of suspended solids (5 and 20 mg/L) or humic acids (2 and 5 mg/L) in the water. Mechanism analysis revealed that during the disinfection process of EBE-MW-UV, microbial DNA and proteins were initially damaged, which prevented the occurrence of dark repair and led to bacterial inactivation. In addition, UV irradiation led to the production of additional reactive oxygen species (ROS) inside the cells, increasing cell membrane permeability and exacerbating membrane damage. This was accompanied by a decrease in energy metabolism and depletion of ATP, ultimately resulting in microbial inactivation. Therefore, EBE-MW-UV demonstrated more effective disinfection than single-wavelength UV-LEDs, showing great potential. Our research gives new insights into the characteristics of multiple wavelength ultraviolet, and provides scientific basis for the selection of new light sources in the field of ultraviolet disinfection.

Wavelength synergistic effects in continuous flow-through water disinfection systems

The past decade's development of UV LEDs has fueled significant research in water disinfection, with widespread debate surrounding the potential synergies of multiple UV wavelengths. This study analyses the use of three UV sources (265, 275, and 310 nm) on the inactivation of Escherichia coli bacteria in two water matrixes. At maximum intensity in wastewater, individual inactivation experiments in a single pass set-up (Flow rate = 2 L min-1, Residence time = 0.75 s) confirmed the 265 nm light source to be the most effective (2.2 ± 0.2 log units), while the 310 nm led to the lowest inactivation rate (0.0003 ± 7.03× 10-5 log units). When a combination of the three wavelengths was used, an average log reduction of 4.4 ± 0.2 was observed in wastewater. For combinations of 265 and 275 nm, the average log reductions were similar to the sum of individual log reductions. For combinations involving the use of 310 nm, a potential synergistic effect was investigated by the use of robust statistical analysis techniques. It is concluded that combinations of 310 nm with 265 nm or 275 nm devices, in sequential and simultaneous mode, present a significant synergy at both intensities due to the emission spectra of the selected LEDs, ensuring the possibility of two inactivation mechanisms. Finally, the electrical energy per order of inactivation found the three-wavelength combination to be the most energy efficient (0.39 ± 0.05, 0.36 ± 0.01 kWh m-3, at 50% and 100% dose, respectively, in wastewater) among the synergistic combinations.

Comparison of Legionella pneumophila and Pseudomonas fluorescens Quantification Methods for Assessing UV LED Disinfection

This study assesses the efficacy of ultraviolet light-emitting diodes (UV LEDs) for deactivating Legionella pneumophila (pure culture) and Pseudomonas fluorescens (pure culture and biofilms) on relevant drinking water distribution system surfaces (cast iron and stainless steel). UV LED treatment at 280 nm demonstrated superior performance compared to that at 365 nm, achieving a 4.8 log reduction value (LRV) for P. fluorescens pure cultures and, for biofilms, 4.02 LRV for stainless steel and 2.96 LRV for cast iron at 280 nm. Conversely, the results were less effective at 365 nm, with suspected photolytic reactions on cast iron. Quantification of L. pneumophila yielded varying results: 4 LRV using standard plate counts, 1.8 LRV with Legiolert, and 1 LRV with quantitative polymerase chain reaction at 280 nm, while the results were less than 1.5 LRV at 365 nm. This study provides insights into managing opportunistic pathogens and biofilms, emphasizing the need for improved quantification tools to better assess treatment efficacy.

Tailored hybrid microbial water disinfection system using sequentially assembled microbial fuel cells and an ultraviolet C light-emitting diode

An integrated ultraviolet C light-emitting diode (UV-C LED) water disinfection system activated by microbial fuel cells (MFCs) was developed, and optimized via electric circuit and device voltage profiling. The intensity of the renewable energy operated, self-powered UV-C LED for E. coli inactivation was calculated by bio-dosimetry to be 2.4  × 10-2 μW cm-2 using fluence-based rate constant (k) of ∼1.03 (±0.11) cm2/mJ to obtain the reduction equivalent fluence kinetics value. Finally, the first-order rate constant for E. coli inactivation during the tailored hybrid disinfection system was found to be 0.53 (±0.1) cm2/mJ by multiplying intensity with 1.09 (±0.1) × 10-5 s-1 derived from the linear regression of E. coli inactivation as a function of time. Furthermore, selected model microbial consisting of two bacteria (Salmonella sp. and Listeria sp.) and three viruses (MS2 bacteriophage, influenza A virus, and murine norovirus-1) were treated with UV-C LED irradiation under controlled experimental conditions to validate the disinfection efficiency of the system. Consequently, the required to achieve significant removal (i.e., >3-log; 99.9%) UV fluence and dose time were calculated to be 4-7 cm2/mJ and 54-76 h and 33-53 cm2/mJ and 400-622 h for model bacterial and viral, respectively. This study expands the applicability of microbial electrochemical system (MES) for microbial disinfection and could be utilized in future MFCs implementation studies for predicting and measuring the kinetics of microbial elimination using a tailored hybrid water treatment system.

Efficacy of UV and UV-LEDs Irradiation Models for Microbial Inactivation Applicable to Automated Sterile Drug Compounding

LEDs development has attracted attention over conventional mercury lamps for the tiny size, high efficiency, long lifetime, low operating temperature. The antimicrobial effectiveness of traditional UV-lamps radiation (wavelength of 254 nm) compared to UV-C LEDs (LED1 wavelength range 275-286 nm and LED2 range 260-270 nm) was carried out, for possible applications to automated sterile drug compounding. The UV lamp and the tested UV-LED devices remarkably reduced microbial load, following a time-dose response, but the best performance was evidenced by LED1, which guaranteed the complete inactivation of high concentrations of bacteria, yeasts, and spores at doses between 200 and 2000 J/m2.

Simultaneous Irradiation with UV-A, -B, and -C Lights Promotes Effective Decontamination of Planktonic and Sessile Bacteria: A Pilot Study

Surfaces in highly anthropized environments are frequently contaminated by both harmless and pathogenic bacteria. Accidental contact between these contaminated surfaces and people could contribute to uncontrolled or even dangerous microbial diffusion. Among all possible solutions useful to achieve effective disinfection, ultraviolet irradiations (UV) emerge as one of the most "Green" technologies since they can inactivate microorganisms via the formation of DNA/RNA dimers, avoiding the environmental pollution associated with the use of chemical sanitizers. To date, mainly UV-C irradiation has been used for decontamination purposes, but in this study, we investigated the cytotoxic potential on contaminated surfaces of combined UV radiations spanning the UV-A, UV-B, and UV-C spectrums, obtained with an innovative UV lamp never conceived so far by analyzing its effect on a large panel of collection and environmental strains, further examining any possible adverse effects on eukaryotic cells. We found that this novel device shows a significant efficacy on different planktonic and sessile bacteria, and, in addition, it is compatible with eukaryotic skin cells for short exposure times. The collected data strongly suggest this new lamp as a useful device for fast and routine decontamination of different environments to ensure appropriate sterilization procedures.

Improved disinfection performance for 280 nm LEDs over 254 nm low-pressure UV lamps in community wastewater

Ultraviolet (UV) disinfection has been incorporated into both drinking water and wastewater treatment processes for several decades; however, it comes with negative environmental consequences such as high energy demands and the use of mercury. Understanding how to scale and build climate responsive technologies is key in fulfilling the intersection of UN Sustainable Development Goals 6 and 13. One technology that addresses the drawbacks of conventional wastewater UV disinfection systems, while providing a climate responsive solution, is UV light emitting diodes (LEDs). The objective of this study was to compare performance of bench-scale 280 nm UV LEDs to bench-scale low pressure (LP) lamps and full-scale UV treated wastewater samples. Results from the study demonstrated that the UV LED system provides a robust treatment that outperformed LP systems at the bench-scale. A comparison of relative energy consumptions of the UV LED system at 20 mJ cm^-2 and LP system at 30 and 40 mJ cm^-2 was completed. Based on current projections for wall plug efficiencies (WPE) of UV LED it is expected that the energy consumption of LED reactors will be on par or lower compared to the LP systems by 2025. This study determined that, at a WPE of 20%, the equivalent UV LED system would lead to a 24.6% and 43.4% reduction in power consumption for the 30 and 40 mJ cm^-2 scenarios, respectively.

Microbial inactivation kinetics of UV LEDs and effect of operating conditions: A methodological critical analysis

Tiny ultraviolet (UV) light-emitting diodes (LED)s that are replacing the conventional energy-intensive mercury UV lamps have gained interest since the early 2000's because of their promising advantages. In the context of microbial inactivation (MI) of waterborne microbes, disinfection kinetics of those LEDs exhibited variations among studies, in terms of varying the UV wavelength, the exposure time, power, and dose (UV fluence) as well as other operational conditions. While reported results may appear contradictory when examined separately, they probably are not when analyzed collectively. As such, in this study, we carry out a quantitative collective regression analysis of the reported data to shed light on the kinetics of MI by the emerging UV LEDs technology alongside the effects of varying operational conditions. The main goal is to identify dose response requirements for UV LEDs and to compare them to traditional UV lamps in addition to ascertaining optimal settings that could help in achieving the optimal inactivation outcome for comparable UV doses. The analysis showed that kinetically, UV LEDs are as effective as conventional mercury lamps for water disinfection, and at times more effective, especially for UV resistant microbes. We defined the maximal efficiency at two wavelengths, 260-265 nm and 280 nm, among a wide range of available LED wavelengths. We also defined the UV fluence per log inactivation of tested microbes. At the operational level, we identified existing gaps and developed a framework for a comprehensive analysis program for future needs.

Near dissolved organic matter microfiltration (NDOM MF) coupled with UVC LED disinfection to maximize the efficiency of water treatment for the removal of Giardia and Cryptosporidium

Microfiltration (MF) membranes with a mean pore size same as or smaller than 0.45 µm have been typically used to separate pathogenic protozoa in water since materials larger than 0.45 µm are considered particulates. However, 0.45 µm is too small to separate protozoa which are 4-6 µm (Cryptosporidium oocyst) or 8-15 µm (Giardia cyst) in size. In this study, we optimized the mean pore size of MF membranes to maximize the producibility and guarantee a high removal rate simultaneously and proposed the membrane filtration using an MF membrane with an optimum mean pore size larger than but close to dissolved organic matter (DOM), which is called near DOM MF (NDOM MF). According to the MF test using polystyrene surrogate beads with diameters of 3 and 8 µm, an MF membrane with a 0.8 µm mean pore size was the best in that it showed 52% to 146% higher water fluxes than a 0.45 µm MF membrane while maintaining the removal rate at 3-4 log. It was also the case for a low-temperature MF test, revealing the NDOM MF is highly effective regardless of temperature changes. Lastly, we tried to find the possibility of combining the NDOM MF with disinfection by an ultraviolet light emitting diode (UVC LED) to further guarantee the high quality of treated water while providing high process efficiency.

Strategies for safe management of hospital wastewater during the COVID-19 pandemic

Management of hospital wastewater is a challenging task, particularly during the situations like coronavirus 2019 (COVID-19) pandemic. The hospital effluent streams are likely to contain many known and unknown contaminants including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) along with a variety of pollutants arising from pharmaceuticals, life-style chemicals, drugs, radioactive species, and human excreta from the patients. The effluents are a mixed bag of contaminants with some of them capable of infecting through contact. Hence, it is essential to identify appropriate treatment strategies for hospital waste streams. In this work, various pollutants emerging in the context of COVID-19 are examined. A methodical review is conducted on the occurrence and disinfection methods of SARS-CoV-2 in wastewater. An emphasis is given to the necessity of addressing the challenges of handling hospital effluents dynamically involved during the pandemic scenario to ensure human and environmental safety. A comparative evaluation of disinfection strategies makes it evident that the non-contact methods like ultraviolet irradiation, hydrogen peroxide vapor, and preventive approaches such as the usage of antimicrobial surface coating offer promise in reducing the chance of disease transmission. These methods are also highly efficient in comparison with other strategies. Chemical disinfection strategies such as chlorination may lead to further disinfection byproducts, complicating the treatment processes. An overall analysis of various disinfection methods is presented here, including developing methods such as membrane technologies, highlighting the merits and demerits of each of these processes. Finally, the wastewater surveillance adopted during the COVID-19 outbreak is discussed.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13762-023-04803-1.

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.

Synergistic disinfection of aerosolized bacteria and bacteriophage by far-UVC (222-nm) and negative air ions

Air ionizers and 222-nm krypton-chlorine (KrCl) excilamp have proven to be effective disinfection apparatus for bacteria and viruses with limited health risks. We determined inactivation efficiencies by operating them individually and in combined modules. Gram-positive and gram-negative bacteria, non-enveloped dsDNA virus, and enveloped dsRNA virus were examined in a designed air disinfection system. Our results showed that the bioaerosols were inactivated efficiently by negative ionizers and far-UVC (222-nm), either used individually or in combination. Among which the combined modules of negative ionizers and KrCl excilamp had the best disinfection performance for the bacteria. The aerosolized virus P22 and Phi 6 were more susceptible to 222-nm emitted by KrCl excilamp than negative air ions. Significant greater inactivation of bacterial bioaerosols were identified after treated by combined treatment of negative air ion and far-UVC for 2 minutes (Escherichia coli, 6.25 natural log (ln) reduction; Staphylococcus epidermidis, 3.66 ln reduction), as compared to the mean sum value of inactivation results by respective individual treatment of negative ionizers and KrCl excilamp (Escherichia coli, 4.34 ln; Staphylococcus epidermidis, 1.75 ln), indicating a synergistic inactivation effect. The findings provide important baseline data to support the design and development of safe and high-efficient disinfection systems.

Continuous and Pulsed Ultraviolet-C LED on Germicidal Effect and Energy Consumption in Fresh Products: Applications in Tomatoes as a Model

Nowadays, lifestyle change is one of the problems of the new world economic order, and the procedures of feeding, purchasing, preparation, and the storage of food products, are forcing authorities to establish more rigorous methods concerning the control of food quality and safety. Owing quality in the agro-food sector is a complex and global issue, due to the distance between production and final consumption, as well as the new demands of society on food. Contributing to the bacteria minimization during their path in the supply chain, the objective of this research is the use of an UV-C LED artificial lighting system with emission in continuous light (CL) and two of pulsed light (Mode 1 and Mode 2) for fresh products' disinfection. A mathematical model is introduced as a reference to establish the equivalence dose of continuous and pulsed UV-C LED irradiation. The doses applied were 5, 15, and 25 mJ cm^-². The configured parameters per each technique were the irradiance, time also the frequency (500 Hz), and duty cycle (30, 50, and 80%) for Mode 1 and Mode 2. The germicidal effect (GE), energy consumption, and effective germicidal effect (EGE), were evaluated for the different techniques. According to the results, the technique Mode 1 was the best in the GE with 1.06 ± 0.01 and 1.08 ± 0.01 Log reduction by 25 mJ cm^-2 at 30 and 80% duty cycle, correspondingly. The CL and Mode 1 showed an outstanding performance with the EGE. Finally, Mode 1 reduced 11% in energy and the GE is comparable with CL. The pulsed light technique Mode 1 constitutes a powerful method against the microorganism's destruction and a strategy for saving energy during the treatment. The UV-C LEDs proved to be an excellent alternative in the disinfection of fresh products with pulsed light emission in the real process.

Protocol for Evaluating the Microbial Inactivation of Commercial UV Devices on Plastic Surfaces

With the plethora of commercially available UV-C devices exhibiting different intensity and lifespans, it is critical to consumer safety that companies verify and clearly communicate the efficacy of their devices as per the intended use. The purpose of this study was to define a low-cost protocol for investigating the antimicrobial efficacy of commercial UV devices for industry use. The tested devices included: a wall-mounted unit (Device A), a troffer unit (Device B), and an induction lamp unit (Device C). The devices were installed within an enclosed tower to prevent the transmission of UV-C radiation outside of the testing area. The procedure details determining the devices' antimicrobial efficacy using plastic coupons inoculated with Escherichia coli or Staphylococcus aureus. The protocol includes suggested time-distance treatments according to the potential application of each device type and reports the results as log CFU/mL reduction or percent reduction.

Systematic evaluating and modeling of SARS-CoV-2 UVC disinfection

The ongoing COVID-19 global pandemic has necessitated evaluating various disinfection technologies for reducing viral transmission in public settings. Ultraviolet (UV) radiation can inactivate pathogens and viruses but more insight is needed into the performance of different UV wavelengths and their applications. We observed greater than a 3-log reduction of SARS-CoV-2 infectivity with a dose of 12.5 mJ/cm² of 254 nm UV light when the viruses were suspended in PBS, while a dose of 25 mJ/cm² was necessary to achieve a similar reduction when they were in an EMEM culture medium containing 2%(v/v) FBS, highlighting the critical effect of media in which the virus is suspended, given that SARS-CoV-2 is always aerosolized when airborne or deposited on a surface. It was found that SARS-CoV-2 susceptibility (a measure of the effectiveness of the UV light) in a buffer such as PBS was 4.4-fold greater than that in a cell culture medium. Furthermore, we discovered the attenuation of UVC disinfection by amino acids, vitamins, and niacinamide, highlighting the importance of determining UVC dosages under a condition close to aerosols that wrap the viruses. We developed a disinfection model to determine the effect of the environment on UVC effectiveness with three different wavelengths, 222 nm, 254 nm, and 265 nm. An inverse correlation between the liquid absorbance and the viral susceptibility was observed. We found that 222 nm light was most effective at reducing viral infectivity in low absorbing liquids such as PBS, whereas 265 nm light was most effective in high absorbing liquids such as cell culture medium. Viral susceptibility was further decreased in N95 masks with 222 nm light being the most effective. The safety of 222 nm was also studied. We detected changes to the mechanical properties of the stratum corneum of human skins when the 222 nm accumulative exposure exceeded 50 J/cm².The findings highlight the need to evaluate each UV for a given application, as well as limiting the dose to the lowest dose necessary to avoid unnecessary exposure to the public.

UV surface disinfection in a wearable drug delivery device

The advent of recombinant DNA technology fundamentally altered the drug discovery landscape, replacing traditional small-molecule drugs with protein and peptide-based biologics. Being susceptible to degradation via the oral route, biologics require comparatively invasive injections, most commonly by intravenous infusion (IV). Significant academic and industrial efforts are underway to replace IV transport with subcutaneous delivery by wearable infusion devices. To further complement the ease-of-use and safety of disposable infusion devices, surface disinfection of the drug container can be automated. For ease of use, the desired injector is a combination device, where the drug is inside the injector as a single solution combination device. The main obstacle of the desired solution is the inability to sterilize both injector and drug in the same chamber or using the same method (Gamma for the drug and ETO for the injector). This leads to the assembly of both drug container and injector after sterilization, resulting in at least one transition area that is not sterilized. To automate the delivery of the drug to the patient, a disinfection step before the drug delivery through the injector is required on the none-sterilized interface. As an innovative solution, the autoinjector presented here is designed with a single ultraviolet light-emitting diode (UV LED) for surface disinfection of the drug container and injector interface. In order to validate microbial disinfection similar to ethanol swabbing on the injector, a bacterial 3 or 6 log reduction needed to be demonstrated. However, the small disinfection chamber surfaces within the device are incapable of holding an initial bacterial load for demonstrating the 3 or 6 log reduction, complicating the validation method, and presenting a dilemma as to how to achieve the log reduction while producing real chamber conditions. The suggested solution in this paper is to establish a correlation model between the UV irradiance distribution within the disinfection chamber and a larger external test setup, which can hold the required bacterial load and represents a worse-case test scenario. Bacterial log reduction was subsequently performed on nine different microorganisms of low to high UV-tolerance. The procedure defined herein can be adopted for other surface or chamber disinfection studies in which the inoculation space is limited.

Dual-wavelength light radiation for synergistic water disinfection

Development of the narrow-band mercury-free light sources, such as light emitting diodes (LEDs) and excilamps, has stimulated research on inactivation of pathogenic microorganisms by dual-wavelength light radiation. To date, dual-wavelength light radiation has emerged as an advanced tool for enhancing microbial inactivation in water in view of potential synergistic effect. This is the first review that aims at elucidating its mechanisms under dual-wavelength light exposure and surveying a body of related literature in terms of yes-or-no synergy. We have proposed three key inactivation mechanisms, which function in the estimated spectrum ranges I (190-254 nm), II (250-320 nm) and III (300-405 nm) and provide a synergistic effect when combined. These mechanisms involve proteins damage and DNA repair suppression (I), direct and indirect DNA damage (II) and generation of reactive oxygen species (ROS) by endogenous photosensitizers (III), such as porphyrins and flavins. A synergy under dual-wavelength light irradiation simultaneously or sequentially occurs if coupling two wavelengths of different ranges (I + II, I + III, II + III) in order to trigger different inactivation mechanisms. Recent advances of dual-wavelength light strategy in photodynamic therapy could be applied for water disinfection. They bring opportunities for applying the sources of near-UV and visible radiation and making the disinfection processes more energy- and cost-effective. From this standpoint, the synergistically efficient dual-wavelength combinations II + III and the combinations within the extended to 700 nm range III (near-UV + VIS) appear to be promising for developing novel advanced oxidation processes for disinfection of real turbid waters.

Current insights into non-thermal preservation technologies alternative to conventional high-temperature short-time pasteurization of drinking milk

Milk is an important nutritional food source characterized by a perishable nature and conventionally thermally treated to guarantee its safety. In recent years, an increasing focus on competing non-thermal food processing technologies has been driven mainly by consumers' expectations for minimally processed products. Due to the heat sensitivity of milk, much research interest has been addressed to mild non-thermal pasteurization processing to keep safety, 'fresh-like' taste and to maintain the organoleptic qualities of raw milk. This review provides an overview of the current literature on non-thermal treatments as standalone alternative technologies to high-temperature short-time (HTST) pasteurization of drinking milk. Results of lab-scale experimentations suggest the feasibility of most emerging non-thermal processing technologies, including high hydrostatic pressure, pulsed electric field, cold plasma, cavitation and light-based technologies, as alternative to thermal treatment of drinking milk with premium in shelf life duration. Nevertheless, a series of regulatory, technological and economical hurdles hinder the industrial scaling-up for most of these substitutes. To date, only high hydrostatic pressure treatments are applied as alone alternative to HTSH pasteurization for processing of "cold pasteurized" drinking milk. Milk submitted to HTST treatment combined to ultraviolet light is currently accepted in EU countries as novel food.

Certain Listeria monocytogenes plasmids contribute to increased UVC ultraviolet light stress

Listeria monocytogenes is the causative agent of the highly fatal foodborne disease listeriosis and can persist in food production environments. Recent research highlights the involvement of L. monocytogenes plasmids in different stress response mechanisms, which contribute to its survival in food production facilities. Ultraviolet (UV) light in the UVC spectrum (200–280 nm) is used in food production to control microbial contamination. Although plasmid-encoded UV resistance mechanisms have been described in other bacteria, no research indicates that L. monocytogenes plasmids contribute to the UV stress response. The plasmids of L. monocytogenes strains 6179, 4KSM and R479a are genetically distinct and were utilized to study the roles of plasmids in the UV response. Wild-type and plasmid-cured variant cells were grown to logarithmic or late-stationary phase, plated on agar plates and exposed to UVC for 60 or 90 s, and colony-forming units (CFUs) were determined. CFUs of 6179 and 4KSM, bearing pLM6179 and p4KSM, respectively, were significantly (P-value < 0.05) higher than those of the plasmid-cured strains in both logarithmic and stationary phases. No difference in survival was observed for the R479a strain. Our data show for the first time that certain L. monocytogenes plasmids contribute to the survival of UVC light stress.

Disinfection Performance of a Drinking Water Bottle System With a UV Subtype C LED Cap Against Waterborne Pathogens and Heterotrophic Contaminants

The purgaty One systems (cap+bottle) are portable stainless-steel water bottles with UV subtype C (UVC) disinfection capability. This study examines the bottle design, verifies disinfection performance against Escherichia coli, Pseudomonas aeruginosa, Vibrio cholerae, and heterotrophic contaminants, and addresses the public health relevance of heterotrophic bacteria. Bottles were inoculated with deliberately contaminated potable water and disinfection efficacy examined using colony forming unit (CFU) assay for each bacterial strain. The heterotrophic plate count (HPC) method was used to determine the disinfection performance against environmental contaminants at day 0 and after 3days of water in stationary condition without prior UVC exposure. All UVC irradiation experiments were performed under stationary conditions to confirm that the preset application cycle of 55s offers the desired disinfection performance under-tested conditions. To determine effectiveness of purgaty One systems (cap+bottle) in disinfection, inactivation efficacy or log reduction value (LRV) was determined using bacteria concentration between UVC ON condition and controls (UVC OFF). The study utilized the 16S ribosomal RNA (rRNA) gene for characterization of isolates by identifying HPC bacteria to confirm if they belong to groups that are of public health concern. Purgaty One systems fitted with Klaran UVC LEDs achieved 99.99% inactivation (LRV4) efficacy against E. coli and 99.9% inactivation (LRV3) against P. aeruginosa, V. cholerae, and heterotrophic contaminants. Based on the 16S rRNA gene analyses, the study determined that the identified HPC isolates from UVC irradiated water are of rare public health concern. The bottles satisfactorily inactivated the target pathogenic bacteria and HPC contaminants even after 3days of water in stationary condition.

Comprehensive Study of Light-Emitting Diodes (LEDs) and Ultraviolet-LED Lights Application in Food Quality and Safety

Light-Emitting Diodes (LEDs) and Ultraviolet Light-Emitting Diodes (UV LEDs) consist in a semiconductor of light, that are emerging in the market, due to their singular characteristics, as being a solid-state cold source of light, which has potential application in food preservation. For this reason, this study lens to provide a review of the effects of LED and UV LED application in fresh fruits and vegetables, under refrigeration storage. Analyzing the LED role, in extending the shelf-life of postharvest food, these present the capability of improving the quality physicochemical and microbiological of fruits and vegetables, such as: color (chlorophyll), weight loss, total phenolic and flavonoid content, phenylalanine ammonia-lyase activity and total soluble solids. In addition, it’s able to stop chemical reactions and increasing the activity of fruits and vegetable defenses. UV LED light, on the other hand, operates in an effective and straightway in the inactivation the food pathogens, such as Escherichia coli, Pseudomonas fluorescens and Salmonella spp, for example. Therefore, UV LED light can be applied to delay the senescence of foods, however, the wavelength must match the target organism, depending on the food.

UV Light Application as a Mean for Disinfection Applied in the Dairy Industry

Thermal treatment is the most popular decontamination technique used in the dairy industry to ensure food protection and prolong shelf life. But it also causes nutrient and aroma degradation, non-enzymatic browning, and organoleptic changes of dairy products. Non-thermal solutions, on the other hand, have been extensively explored in a response to rising market demand for more sustainable and safe goods. For a long time, the use of ultraviolet (UV) light in the food industry has held great promise. Irradiation with shortwave UV light has excellent germicidal properties, which can destroy a variety of microbial pathogens (for example bacteria, fungi, molds, yeasts, and viruses), at low maintenance and installation costs with minimal use of energy to preserve food without undesirable effects of heat treatment. The purpose of this review is to update the studies made on the possibilities of UV-C radiation while also addressing the essential processing factors involved in the disinfection. It also sheds light on the promise of UV light-emitting diodes (UV-LEDs) as a microbial inactivation alternative to conventional UV lamps.

Effects of Combined Aerosolization with Ultraviolet C Light-Emitting Diode on Enterohemorrhagic Escherichia coli and Staphylococcus aureus Attached to Soft Fresh Produce

Washing soft fresh produce such as strawberries, baby leaves, and sliced onions with sanitizing agents is challenging due to their fragile texture. Thus, treatments like aerosolization using slightly acidic electrolyzed water (SAEW) and ultraviolet C light-emitting diode (UVC LED) irradiation may be good alternatives. In the present study, the reduction effects of a combined treatment of aerosolization using SAEW and UVC LED irradiation on enterohemorrhagic Escherichia coli (EHEC) and Staphylococcus aureus attached to strawberries, baby leaves, and sliced onions were investigated. The behaviours of EHEC and S. aureus, moisture loss, colour measurement, and visual appearance were also analyzed at 10 and 15 °C for 7 days. The reduction effect of the combined treatment with 100 SAEW and UVC LED was higher (0.53–0.92 log CFU g⁻¹) than a single aerosolization treatment (0.11–0.41 log CFU g⁻¹), regardless of samples or pathogens. A greater effect on EHEC and S. aureus reduction was observed in strawberries (0.74 and 0.92 log CFU g⁻¹) than in baby leaves (0.62 and 0.53 log CFU g⁻¹) and sliced onions (0.55 and 0.62 log CFU g⁻¹). The combined treatment further reduced the EHEC and S. aureus populations in strawberries during 7 days of storage at 10 and 15 °C. However, the EHEC and S. aureus populations were maintained in baby leaves and sliced onions at 10 °C for 7 days. Additionally, the greatest effect on the maintenance of colour and appearance was obtained in the combined treatment. Since the combined treatment reduces EHEC and S. aureus populations and preserves visual quality, it could be expected to extend the shelf life of soft fresh produce at the retailer stage of the supply chain.

Control Measures of Pathogenic Microorganisms and Shelf-Life Extension of Fresh-Cut Vegetables

We investigated the combined effect of using slightly acidic electrolyzed water (SAEW), ultrasounds (US), and ultraviolet-C light-emitting diodes (UV-C LED; 275 nm) for decreasing pathogenic Escherichia coli and Staphylococcus aureus (SEA) in fresh-cut vegetables, including carrots, celery, paprika, and cabbage. Survival of pathogenic E. coli and SEA and quality properties of fresh-cut vegetables at 5 and 15 °C for 7 days were also investigated. When combined treatment (SAEW + US + UV-C LED) was applied to fresh-cut vegetables for 3 min, its microbial reduction effect was significantly higher (0.97~2.17 log CFU/g) than a single treatment (p < 0.05). Overall, the reduction effect was more significant for SEA than for pathogenic E. coli. At 5 °C, SAEW + US and SAEW + US + UV-C LED treatments reduced populations of pathogenic E. coli and SEA in all vegetables. At 15 °C, SAEW + US + UV-C LED treatment inhibited the growth of both pathogens in carrot and celery and extended the shelf life of fresh-cut vegetables by preventing color changes in all vegetables. Although the effects of treatments varied depending on the characteristics of the vegetables and pathogens, UV-C LED can be suggested as a new hurdle technology in fresh-cut vegetable industry.

Development of Antimicrobial Phototreatment Tolerance: Why the Methodology Matters

Due to rapidly growing antimicrobial resistance, there is an urgent need to develop alternative, non-antibiotic strategies. Recently, numerous light-based approaches, demonstrating killing efficacy regardless of microbial drug resistance, have gained wide attention and are considered some of the most promising antimicrobial modalities. These light-based therapies include five treatments for which high bactericidal activity was demonstrated using numerous in vitro and in vivo studies: antimicrobial blue light (aBL), antimicrobial photodynamic inactivation (aPDI), pulsed light (PL), cold atmospheric plasma (CAP), and ultraviolet (UV) light. Based on their multitarget activity leading to deleterious effects to numerous cell structures-i.e., cell envelopes, proteins, lipids, and genetic material-light-based treatments are considered to have a low risk for the development of tolerance and/or resistance. Nevertheless, the most recent studies indicate that repetitive sublethal phototreatment may provoke tolerance development, but there is no standard methodology for the proper evaluation of this phenomenon. The statement concerning the lack of development of resistance to these modalities seem to be justified; however, the most significant motivation for this review paper was to critically discuss existing dogma concerning the lack of tolerance development, indicating that its assessment is more complex and requires better terminology and methodology.

Effects of ultraviolet-C light-emitting diodes at 275 nm on inactivation of Alicyclobacillusacidoterrestris vegetative cells and its spores as well as the quality attributes of orange juice

Alicyclobacillus acidoterrestris is a thermoacidophilic, spore-forming bacillus. A. acidoterrestris and its spores can survive in pasteurized juices and cause microbial spoilage. In this work, the effects of ultraviolet-C light-emitting diodes at 275 nm on the inactivation of A. acidoterrestris vegetative cells and its spores in commercial pasteurized orange juice were studied. Meanwhile, the effects of ultraviolet-C light-emitting diodes on the quality attributes of the orange juice were also investigated. The quantities of A. acidoterrestris vegetative cells and its spores inoculated in orange juice were reduced by 6.04 and 2.49 log₁₀ CFU/mL after ultraviolet-C light-emitting diode treatment at 220 mJ/cm², respectively. The Weibull and Weibull plus tail models were satisfactorily fitted to estimate the reductions of A. acidoterrestris vegetative cells and its spores in orange juice, respectively. Physicochemical properties (pH, titratable acidity, total soluble solids, and clarity) of orange juice did not change significantly after exposure to ultraviolet-C light-emitting diodes. However, the total phenolic content of orange juice decreased with increasing fluence. In addition, ultraviolet-C light-emitting diode treatment at a higher fluence led to a noticeable color difference. These results indicate that ultraviolet-C light-emitting diode treatment has a potential application in the juice processing industry.

A novel upper-room UVC-LED irradiation system for disinfection of indoor bioaerosols under different operating and airflow conditions

The potential of inactivating indoor bacteria aerosols using a novel rotating ultraviolet-C (UV-C) light-emitting-diode (LED) system was investigated. The system was installed in the upper level of a full scale chamber and its effectiveness against aerosolized E. coli, S. marcescens, and S. epidermidis under the well-mixed with stationary UV-LED scenario was initially tested. The estimated susceptibility values were 1.068, 1.148, and 0.156 m²/J for E. coli, S. marcescens, and S. epidermidis, respectively. Three additional scenarios of experiments were conducted, in which E. coli was aerosolized into the test chamber and then allowed to decay under (i) poorly-mixed condition with stationary system, (ii) well-mixed with rotating system, and (iii) poorly-mixed conditions with rotating system. Our results showed no significant difference between the performance of stationary and rotating UR-UVGI-LED systems under a well-mixed condition. While the performance of the stationary UR-UVGI-LED system under a poorly-mixed condition decreased by 52.90-79.38 % compared to a well-mixed condition, rotating the UR-UVGI-LED system under a poorly-mixed condition, compared to the stationary system, enhanced its performance by 22.36-49.86 %. Thus, our proposed rotating irradiation offers great potential for application in environments where bioaerosols are unevenly distributed in a built environment.

Effects of single and combined UV-LEDs on inactivation and subsequent reactivation of E. coli in water disinfection

Ultraviolet light emitting diodes (UV-LEDs) have shown a potential to replace traditional Ultraviolet (UV) pressure lamps for water disinfection. However, the research is not sufficient and hence, it is still difficult to make any logical conclusions. In this work, UV-LEDs with peak emissions at 267, 275, 310 nm and combined emissions at 267/275, 267/310 and 275/310 nm were applied to a batch water disinfection system. Under either single- or combined-wavelength situation, the inactivation efficiency, reactivation (due to photoreactivation and dark repair) after UV irradiation and electrical energy consumption were evaluated by way of the model bacterium Escherichia coli. It was found that, the 267 nm UV-LED had the highest inactivation efficiency than other UV-LEDs. Although reactivation occurred after 267, 275, 267/275 and 275/310 nm UV-LEDs' irradiations, it occurred to a lesser extent in dark repair than in photoreactivation, demonstrating that photo-effect is the dominant mechanism of reactivation. In addition, decay phase was more prominent than reactivation in dark repair. However, the irradiation by the 275 nm UV-LED showed a better persistence against reactivation which could be attributed to protein damage at 275 nm. No synergistic effect for combined wavelengths was observed in this study. The electrical energy consumption was lower for the 275 nm UV-LED than the other UV-LEDs which was attributed to its higher wall plug efficiency. This study showed the variation principle between the single and combined UVB/UVC-LEDs in inactivation efficiency, inhibition of reactivation, synergistic effect and electrical energy consumption in treatment of E. coli, which is useful for the reasonable exploitation of UV-LEDs in water disinfection systems.