Bactericidal Effects against S. aureus and Physicochemical Properties of Plasma Activated Water stored at different temperatures

Combating foodborne pathogens: Efficacy of plasma-activated water with supplementary methods for Staphylococcus aureus eradication on chicken, and beef

The research study suggested using plasma-activated water (PAW) along with auxiliary technologies, such as micro/nanobubbles (MNB), ultraviolet (UV) photolysis, and ultrasonication (US), to increase the effectiveness of sterilization. By using Factorial Design of Experiments (DOE) techniques, the characteristics and optimal production that contributed to disinfecting pathogens were assessed. Analysis revealed that Staphylococcus aureus (S. aureus) infection rate was most significantly influenced by factors including duration of MNB, UV, and the interaction term between MNB*UV. The optimal conditions for S. aureus reduction in chicken and beef of 8.41 and 8.20 log10 CFU/ml, respectively, which were found when PAW was combined with UV and US for 20 min of treatment. This study arrives to the conclusion that combining PAW with appropriate supplementary technologies increased efficiency and enhance disinfection effectiveness in chicken and beef which could be implemented for another alternative pathogen inactivation in food industry. © 2017 Elsevier Inc. All rights reserved.

The impact of plasma-activated water on the process of nickel bioremediation by Neowestiellopsis persica A1387

Cyanobacteria provide an economical, feasible, and environmentally friendly solution for heavy metal removal. In addition, plasma can facilitate the removal of heavy metals across various time frames. In this study, we applied plasma-activated water (PAW) to prepare Neowestiellopsis persica A1387 strain medium culture for 0, 10, 15, and 20 min via an Atmospheric Cold Plasma Jet device (ACPJ-17A). Nickel removal efficiency was evaluated after 48 hours of cultivation under controlled conditions at 0, 10, 30, 60, and 90 min. Further investigation was performed through FTIR, GC-MS, and XRD techniques. Statistical analysis of ANOVA and Tukey's test indicated that the samples treated for 15 min had the highest biomass dry weight, polysaccharide content, and nickel removal rate (p ≤ 0.05). The GC-MS analysis presented elevated concentrations of ethanol, 1,3-dimethylbenzene, acetic acid, 3-methylbutyl ester, aromatic chemicals, 2-methyl-1-propanol, and 3-octen-2-ol in all samples treated with plasma. The functional group analysis using the FT-IR approach showed increased peak intensities with more extended treatment periods, indicating the addition of methyl, methylene, and hydroxyl groups to the cyanobacterium cell wall. Furthermore, a peak at 468 cm⁻¹ wavelength was observed, correlating to the Ni-O stretching mode after absorption of Ni on the cyanobacterium surface. The XRD data exhibited prominent peaks in all diffraction patterns angles below 20 degrees, suggesting the presence of amorphous and non-crystalline chemical structures within the cyanobacterial structures. The peak intensity increased with longer treatment durations. The 15-min plasma treatment optimized Ni removal, but the efficiency decreased with prolonged exposure due to adverse effects such as increased reactive oxygen species (ROS) production.

Microbial decontamination of fresh-cut celery using simultaneous ultrasound and plasma-activated water treatment

This study investigated an ultrasound (US) treatment strategy in plasma-activated water (PAW) (UP treatment) to inactivate indigenous aerobic bacteria, Escherichia coli O157:H7, and Listeria monocytogenes in fresh-cut celery. Both plasma discharge and US treatment times contributed to the inactivation of indigenous bacteria in celery. The predicted optimal UP treatment conditions included a discharge time of 61.5 min and treatment time of 338 s, resulting in the inactivation of indigenous bacteria, E. coli O157:H7, and L. monocytogenes by 2.7, 1.7, and 3.2 log CFU/g, respectively. With an increase in plasma discharge time or US treatment time, the oxidation-reduction potential and electrical conductivity values of PAW increased, while the pH decreased. UP treatment effectively inactivated bacteria non-thermally, without altering the color of celery. Furthermore, UP treatment led to an increase in cell lipid peroxidation, reactive oxygen species production, and the number of non-viable E. coli O157:H7 and L. monocytogenes cells with membrane damage. This study highlights the potential of UP treatment for bacterial decontamination of fresh-cut celery.

Multiple RONS-Loaded Plasma-Activated Ice Microneedle Patches for Transdermal Treatment of Psoriasis

Cold atmospheric plasma (CAP) is a fledgling therapeutic technique for psoriasis treatment with noninvasiveness, but clinical adoption has been stifled by the insufficient production and delivery of plasma-generated reactive oxygen and nitrogen species (RONS). Herein, patches of air-discharge plasma-activated ice microneedles (PA-IMNs) loaded with multiple RONS are designed for local transdermal delivery to treat psoriasis as an alternative to direct CAP irradiation treatment. By mixing two RONS generated by the air-discharge plasma in the NOx mode and O3 mode, abundant high-valence RONS are produced and incorporated into PA-IMNs via complex gas-gas and gas-liquid reactions. The PA-IMNs abrogate keratinocyte overproliferation by inducing reactive oxygen species (ROS)-mediated loss of the mitochondrial membrane potential and apoptosis of keratinocytes. The in vivo transdermal treatment confirms that PA-IMNs produce significant anti-inflammatory and therapeutic actions for imiquimod (IMQ)-induced psoriasis-like dermatitis in mice by inhibiting the release of associated inflammatory factors while showing no evident systemic toxicity. Therefore, PA-IMNs have a large potential in transdermal delivery platforms as they overcome the limitations of using CAP directly in the clinical treatment of psoriasis.

Insights into the mechanisms of plasma physicochemical characteristics on ultralong-lasting plasma-activated water: the influence of DC power polarity on RONS generation

In our recent work, we successfully developed an innovative method based on pin-water discharge for preparing ultralong-lasting plasma-activated water (PAW) with a lifetime of up to 720 hours at room temperature. However, the impact of power polarity on the preparation method for ultralong-lasting PAW remains unclear. In this study, we discovered that ultralong-lasting PAW could only be achieved with positive polarity. Further analysis of the liquid reactive oxygen and nitrogen species (RONS) revealed that the absence of H2O2 in the discharge chamber was crucial for the failure of ultralong-lasting PAW preparation at negative polarity. To elucidate the mechanism underlying the generation of RONS at different polarities, we conducted plasma feature diagnosis, compared discharge morphologies, and performed theoretical analyses based on chemical reactions. Our results indicated that the introduction of water vapor molecules through intense spraying at positive polarity led to an increase in the generation of H2O2-related source particles, while also interfering with N2-related electron collision reactions and chemical reaction coefficients, ultimately affecting the production of NO2-. Consequently, there was relatively less liquid NO2- and more abundant H2O2 in the discharge chamber at positive polarity, whereas the opposite trend was observed for these two key RONS at negative polarity. Furthermore, the minimal amount of NO2- at positive polarity and the tiny amount of H2O2 at negative polarity in the discharge chamber would be respectively consumed by the relatively abundant H2O2 at positive polarity and NO2- at negative polarity.

Plasma-Activated Tap Water with Oxidative Potential Has an Inactivating Effect on Microbiological Contaminants in Aqueous Suspensions

Plasma-activated water (PAW) generated from tap water has gained attention as a disinfectant when used directly in its pure form. Little is known about the application of PAW for bacterial inactivation in aqueous environments because its use in fluids results in dilutions. We investigated the effect of PAW in aqueous suspensions simulating such dilutions, and we focused on the minimal addition of PAW volumes to bacterial aqueous suspensions still resulting in high inactivation rates. The antimicrobial effect was highly dependent on the activation of PAW. An increase in activation power from 90 to 100 W resulted in a greater microbial reduction with an identical 10 min activation time. The susceptibility to PAW dilutions was analyzed in detail regarding nine Gram-negative species out of Enterobacterales and other waterborne microorganisms as well as four Gram-positive species present in two different matrices, in saline and in tap water, at high concentrations simulating massive contamination situations. For this purpose, the PAW activation setting of 90 W and 30 min was defined in order to be able to differentiate the limitations of inactivation in individual bacterial species. The Gram-negatives in saline demonstrated susceptibility when one volume unit of PAW was added. However, twice the PAW volume was necessary for inactivation when bacteria were present in tap water. Gram-positive microorganisms were more robust, indicated by prolonged contact times before inactivation. Our results indicate that PAW can be used for bacterial decontamination processes in aqueous environments when added in surplus. Optimized activation settings such as electric power to generate PAW and the contact times to the samples increase the effect of the inactivation a wide range of bacteria, regardless of their resistance profiles.

Comparing Redox and Intracellular Signalling Responses to Cold Plasma in Wound Healing and Cancer

Cold plasma (CP) is an ionised gas containing excited molecules and ions, radicals, and free electrons, and which emits electric fields and UV radiation. CP is potently antimicrobial, and can be applied safely to biological tissue, birthing the field of plasma medicine. Reactive oxygen and nitrogen species (RONS) produced by CP affect biological processes directly or indirectly via the modification of cellular lipids, proteins, DNA, and intracellular signalling pathways. CP can be applied at lower levels for oxidative eustress to activate cell proliferation, motility, migration, and antioxidant production in normal cells, mainly potentiated by the unfolded protein response, the nuclear factor-erythroid factor 2-related factor 2 (Nrf2)-activated antioxidant response element, and the phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway, which also activates nuclear factor-kappa B (NFκB). At higher CP exposures, inactivation, apoptosis, and autophagy of malignant cells can occur via the degradation of the PI3K/Akt and mitogen-activated protein kinase (MAPK)-dependent and -independent activation of the master tumour suppressor p53, leading to caspase-mediated cell death. These opposing responses validate a hormesis approach to plasma medicine. Clinical applications of CP are becoming increasingly realised in wound healing, while clinical effectiveness in tumours is currently coming to light. This review will outline advances in plasma medicine and compare the main redox and intracellular signalling responses to CP in wound healing and cancer.

Stress response of Salmonella Newport with various sequence types toward plasma-activated water: Viable but nonculturable state formation and outer membrane vesicle production

This study aims to investigate the response of Salmonella Newport to plasma-activated water (PAW), a novel disinfectant that attracts attention due to its broad-spectrum antimicrobial efficacy and eco-friendliness. In this work, we demonstrated that S. Newport of different sequence types (STs) could be induced into the viable but nonculturable (VBNC) state by PAW treatment. Notably, a remarkable 99.96% of S. Newport ST45 strain entered the VBNC state after a 12-min PAW treatment, which was the fastest observed among the five S. Newport STs (ST31, ST45, ST46, ST166, ST2364). Secretion of outer membrane vesicles was observed in ST45, suggesting a potential strategy against PAW treatment. Genes related to oxidative stress (sodA, katE, trxA), outer membrane proteins (ompA, ompC, ompD, ompF) and virulence (pagC, sipC, sopE2) were upregulated in the PAW-treated S. Newport, especially in ST45. A reduction of 38-65% in intracellular ATP level after PAW treatment was observed, indicating a contributor to the formation of the VBNC state. In addition, a rapid method for detecting the proportion of VBNC cells in food products based on pagC was established. This study contributes to understanding the formation mechanism of the VBNC state in S. Newport under PAW stress and offers insights for controlling microbial risks in the food industry.

Influence of MHz-order acoustic waves on bacterial suspensions

The development of alternative techniques to efficiently inactivate bacterial suspensions is crucial to prevent transmission of waterborne illness, particularly when commonly used techniques such as heating, filtration, chlorination, or ultraviolet treatment are not practical or feasible. We examine the effect of MHz-order acoustic wave irradiation in the form of surface acoustic waves (SAWs) on Gram-positive (Escherichia coli) and Gram-negative (Brevibacillus borstelensis and Staphylococcus aureus) bacteria suspended in water droplets. A significant increase in the relative bacterial load reduction of colony-forming units (up to 74%) can be achieved by either increasing (1) the excitation power, or, (2) the acoustic treatment duration, which we attributed to the effect of the acoustic radiation force exerted on the bacteria. Consequently, by increasing the maximum pressure amplitude via a hybrid modulation scheme involving a combination of amplitude and pulse-width modulation, we observe that the bacterial inactivation efficiency can be further increased by approximately 14%. By combining this scalable acoustic-based bacterial inactivation platform with plasma-activated water, a 100% reduction in E. coli is observed in less than 10 mins, therefore demonstrating the potential of the synergistic effects of MHz-order acoustic irradiation and plasma-activated water as an efficient strategy for water decontamination.

Recent advances in activated water systems for the postharvest management of quality and safety of fresh fruits and vegetables

Over the last three decades, decontamination management of fresh fruits and vegetables (FFVs) in the packhouses and along the supply chains has been heavily dependent on chemical-based wash. This has resulted in the emergence of resistant foodborne pathogens and often the deposition of disinfectant byproducts on FFVs, rendering them unacceptable to consumers. The management of foodborne pathogens, microbial contaminants, and quality of FFVs are a major concern for the horticultural industries and public health. Activated water systems (AWS), such as electrolyzed water, plasma-activated water, and micro-nano bubbles, have gained significant attention from researchers over the last decade due to their nonthermal and nontoxic mode of action for microbial inactivation and preservation of FFVs quality. The aim of this review is to provide a comprehensive summary of recent progress on the application of AWS and their effects on quality attributes and microbial safety of FFVs. An overview of the different types of AWS and their properties is provided. Furthermore, the review highlights the chemistry behind generation of reactive species and the impact of AWS on the quality attributes of FFVs and on the inactivation/reduction of spoilage and pathogenic microbes (in vivo or in vitro). The mechanisms of action of microorganism inactivation are discussed. Finally, this work highlights challenges and limitations for commercialization and safety and regulation issues of AWS. The synergistic prospect on combining AWS for maximum microorganism inactivation effectiveness is also considered. AWS offers a potential alternative as nonchemical interventions to maintain quality attributes, inactivate spoilage and pathogenic microorganisms, and extend the shelf-life for FFVs.

Atmospheric non-thermal plasma inactivation of Ascosphaera apis, the causative agent of chalkbrood disease in honeybee

Ascosphaera apis is a worldwide pathogenic fungi of honeybees that can cause a decline in bee populations. In this study, we investigated the antifungal activity of non-thermal plasma on fungal growth. Spore inactivation after exposure to gas plasma by liquid phase and plasma activated water (PAW) and pathogenicity of A. apis in vivo were also examined. The results demonstrated that the mycelial growth of fungi was completely inhibited after argon plasma treatment. Both gas plasma and PAW exposures resulted in a significant decrease of A. apis spore numbers, maximum reduction of 1.71 and 3.18-fold, respectively. Germinated fungal spores on potato dextrose agar were also reduced after plasma treatment. SEM analysis revealed a disruption in the morphological structure of the fungal spores. The pathogenicity of A. apis on honeybee larvae was decreased after spores treated by gas plasma and PAW with a disease inhibition of 63.61 ± 7.28% and 58.27 ± 5.87%, respectively after 7 days of cultivation. Chalkbrood in honey bees have limited control options and our findings are encouraging. Here, we demonstrate a possible alternative control method using non-thermal plasma for chalkbrood disease in honeybees.

Cytotoxicity studies and antibacterial modification of poly(ethylene 2,5-furandicarboxylate) nonwoven

Novel poly(ethylene 2,5-furandicarboxylate) PEF nonwovens were produced by solution electrospinning and further modification. To improve the wettability of the hydrophobic nonwovens with water, they were treated with sodium hydroxide. Cytotoxicity tests carried out with human keratinocytes confirmed that the nonwovens did not have a toxic effect on healthy cells. The hydrophilicity of the sodium hydroxide treated nonwoven favored the adherence of the cells and their growth. In turn, the two-step modification of the nonwovens by reactions with (3-mercaptopropyl)methyldimethoxysilane and silver nitrate permitted to deposit silver particles on the fiber surfaces. The bacteria growth inhibition zones around the tested specimens were observed evidencing their antibacterial activity against Escherichia coli and Staphylococcus aureus.

Delivery Systems for Plasma-reactive Species and their Applications in the Field of Biomedicine

Cold atmospheric plasma (CAP) is an ionized matter with potential applications in various medical fields, ranging from wound healing and disinfection to cancer treatment. CAP's clinical usefulness stems from its ability to act as an adjustable source of reactive oxygen and nitrogen species (RONS), which are known to function as pleiotropic signaling agents within cells. Plasma-activated species, such as RONS, have the potential to be consistently and precisely released by carriers, enabling their utilization in a wide array of biomedical applications. Furthermore, understanding the behavior of CAP in different environments, including water, salt solutions, culture medium, hydrogels, and nanoparticles, may lead to new opportunities for maximizing its therapeutic potential. This review article sought to provide a comprehensive and critical analysis of current biomaterial approaches for the targeted delivery of plasma-activated species in the hope to boost therapeutic response and clinical applicability.

Electrical Conductivity and Antibacterial Activity of Woven Fabrics through Quercetin-Assisted Thermal Reduction of a Graphene Oxide Coating

Cotton and poly(ethylene terephthalate) (PET) woven fabrics were coated with graphene oxide (GO) using a padding method and the GO deposited on the fiber surfaces was thermally reduced to impart electrical conductivity to the fabrics. To assist the thermal reduction of GO, quercetin (Q)-a natural flavonoid-was used. To this end, before the reduction, the GO-padded fabrics were immersed in Q solutions in ethanol with different Q concentrations. Q enhanced the thermal reduction of GO. Depending on the Q concentration in the solutions, electrical surface resistivities of the cotton fabric of 750 kΩ/sq to 3.3 MΩ/sq and of the PET fabric of 240 kΩ/sq to 730 kΩ/sq were achieved. The cotton and PET fabrics also became hydrophobic, with water contact angles of 163° and 147°, respectively. In addition to the electrical conductivity, the presence of Q resulted in antibacterial activity of the fabrics against Escherichia coli and Staphylococcus aureus.

A review on plasma-activated water and its application in the meat industry

Meat is a nutritious food with a short shelf life, making it challenging to ensure safety, quality, and nutritional value. Foodborne pathogens and oxidation are the main concerns that lead to health risks and economic losses. Conventional approaches like hot water, steam pasteurization, and chemical washes for meat decontamination improve safety but cause nutritional and quality issues. Plasma-activated water (PAW) is a potential alternative to thermal treatment that can reduce oxidation and microbial growth, an essential factor in ensuring safety, quality, and nutritional value. This review explores the different types of PAW and their physiochemical properties. It also outlines the reaction pathways involved in the generation of short-lived and long-lived reactive nitrogen and oxygen species (RONS) in PAW, which contribute to its antimicrobial abilities. The review also highlights current studies on PAW inactivation against various planktonic bacteria, as well as critical processing parameters that can improve PAW inactivation efficacy. Promising applications of PAW for meat curing, thawing, and decontamination are discussed, with emphasis on the need to understand how RONS in PAW affect meat quality. Recent reports on combining PAW with ultrasound, mild heating, and non-thermal plasma to improve inactivation efficacy are also presented. Finally, the need to develop energy-efficient systems for the production and scalability of PAW is discussed for its use as a potential meat disinfectant without compromising meat quality.

Efficacy of Plasma-Treated Water against Salmonella Typhimurium: Antibacterial Activity, Inhibition of Invasion, and Biofilm Disruption

Plasma-treated water (PTW) has emerged as a potential sanitizing agent. This study evaluated antibacterial activity, inhibition of invasion, and biofilm disruption effects of PTW against Salmonella Typhimurium. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were determined for different PTW types. Time-kill assays were conducted to assess bactericidal effects, while polarized Caco-2 cells were used to evaluate invasion inhibition. Biofilm formation and cell viability were examined following PTW treatment using Salmonella Typhimurium isolates, while biofilm disruption and regrowth prevention were investigated using the Bioflux system. PTW exhibited antibacterial activity against all Salmonella Typhimurium isolates, with MICs of 25% for PTW1 and PTW2, and 50% for PTW3, PTW4, and PTW5. MBCs of 50% in media were observed for all PTW types. Undiluted PTW1 and PTW2 showed the highest bactericidal capacity, significantly reduced Salmonella viability, and completely inhibited bacterial invasion, while PTW3 and PTW5 also showed significant invasion reduction. Bioflux experiments confirmed the eradication of biofilms by PTW1 and PTW2, with no regrowth observed 72 h after PTW was removed. PTW demonstrated significant antibacterial activity, inhibition of invasion, biofilm disruption, and reduction of bacterial viability against Salmonella Typhimurium. This highlights PTW's potential as an effective sanitizer for reducing Salmonella contaminations.

Chemical decontamination of foods using non-thermal plasma-activated water

The presence of chemical contaminants in foods and agricultural products is one of the major safety issues worldwide, posing a serious concern to human health. Nonthermal plasma (NTP) containing richly reactive oxygen and nitrogen species (RONS) has been trialed as a potential decontamination method. Yet, this technology comes with multiple downsides, including adverse effects on the quality of treated foods and limited exposure to entire surfaces on samples with hard-to-reach spots, further hindering real-life applications. Therefore, plasma-activated water (PAW) has been recently developed to facilitate the interactions between RONS and contaminant molecules in the liquid phase, allowing a whole surface treatment with efficient chemical degradation. Here, we review the recent advances in PAW utilized as a chemical decontamination agent in foods. The reaction mechanisms and the main RONS contributors involved in the PAW-assisted removal of chemical contaminants are briefly outlined. Also, the comprehensive effects of these treatments on food qualities (chemical and physical characteristics) and toxicological evaluation of PAW (in vitro and in vivo) are thoroughly discussed. Ultimately, we identified some current challenges and provided relevant suggestions, which can further promote PAW research for real-life applications in the future.

Non-Thermal Atmospheric Pressure Plasma Application in Endodontics

The failure of endodontic treatment is frequently associated with the presence of remaining microorganisms, mainly due to the difficulty of eliminating the biofilm and the limitation of conventional irrigation solutions. Non-thermal atmospheric pressure plasma (NTPP) has been suggested for many applications in the medical field and can be applied directly to biological surfaces or indirectly through activated liquids. This literature review aims to evaluate the potential of NTPP application in Endodontics. A search in the databases Lilacs, Pubmed, and Ebsco was performed. Seventeen manuscripts published between 2007 and 2022 that followed our established inclusion criteria were found. The selected manuscripts evaluated the use of NTPP regarding its antimicrobial activity, in the direct exposure and indirect method, i.e., plasma-activated liquid. Of these, 15 used direct exposure. Different parameters, such as working gas and distance from the apparatus to the substrate, were evaluated in vitro and ex vivo. NTPP showed a disinfection property against important endodontic microorganisms, mainly Enterococcus faecalis and Candida albicans. The antimicrobial potential was dependent on plasma exposure time, with the highest antimicrobial effects over eight minutes of exposure. Interestingly, the association of NTPP and conventional antimicrobial solutions, in general, was shown to be more effective than both treatments separately. This association showed antimicrobial results with a short plasma exposure time, what could be interesting in clinical practice. However, considering the lack of standardization of the direct exposure parameters and few studies about plasma-activated liquids, more studies in the area for endodontic purposes are still required.

Cold-atmospheric-plasma activated-ice as a cooling medium with antimicrobial properties: Case study on fish fillet preservation

The efficacy and applicability of Plasma Activated Ice (PAI) -produced by cold atmospheric plasma (CAP) technology- on microorganisms and quality characteristics of perishable fresh sea bream (Sparus aurata) fillets, were evaluated. The changes in microbiological load and quality characteristics of fish fillets were investigated during storage with ice from deionized water (Control), PAI and ice from artificially produced water (Artificial) of H₂O₂ concentrations equal to those of PAI. Fresh sea bream fillets were packed under ice flakes (produced from PAI or Artificial or Control) on layers (as typically done in the relevant industry) and stored at 0.5 °C for 27 days. PAI application inhibited significantly the growth of microbial load of the fillets resulting in reduced growth rates while simultaneously significantly retarded the quality deterioration compared to the other disinfectant media. The use of PAI (with 10 mg/L H₂O₂) led to a 11-day and 6-day extension, i.e., 2-fold and a ∼ 1.5-fold extension, of the fillets shelf-life compared to the samples treated with Control and Artificial ice, respectively. The results proved the efficiency of PAI in extending the shelf-life of perishable foods during storage (or/and transportation), by validating its antimicrobial properties and cooling capacity.

Physicochemical Properties of Plasma-Activated Water and Its Control Effects on the Quality of Strawberries

In this study, the effects of plasma-activated water (PAW), generated by dielectric barrier discharge cold plasma at the gas–liquid interface, on the quality of fresh strawberries during storage were investigated. The results showed that, with the prolongation of plasma treatment time, the pH of PAW declined dramatically and the electrical conductivity increased significantly. The active components, including NO2−, NO3−, H2O2, and O2−, accumulated gradually in PAW, whereas the concentration of O2− decreased gradually with the treatment time after 2 min. No significant changes were found in pH, firmness, color, total soluble solids, malondialdehyde, vitamin C, or antioxidant activity in the PAW-treated strawberries (p > 0.05). Furthermore, the PAW treatment delayed the quality deterioration of strawberries and extended their shelf life. Principal component analysis and hierarchical cluster analysis showed that the PAW 2 treatment group demonstrated the best prolonged freshness effect, with the highest firmness, total soluble solids, vitamin C, and DPPH radical scavenging activity, and the lowest malondialdehyde and ∆E* values, after 4 days of storage. It was concluded that PAW showed great potential for maintaining the quality of fresh fruits and extending their shelf life.

Efficient inactivation of the contamination with pathogenic microorganisms by a combination of water spray and plasma-activated air

The global pandemic caused by SARS-CoV-2 has lasted two and a half years and the infections caused by the viral contamination are still occurring. Developing efficient disinfection technology is crucial for the current epidemic or infectious diseases caused by other pathogenic microorganisms. Gas plasma can efficiently inactivate different microorganisms, therefore, in this study, a combination of water spray and plasma-activated air was established for the disinfection of pathogenic microorganisms. The combined treatment efficiently inactivated the Omicron-pseudovirus through caused the nitration modification of the spike proteins and also the pathogenic bacteria. The combined treatment was improved with a funnel-shaped nozzle to form a temporary relatively sealed environment for the treatment of the contaminated area. The improved device could efficiently inactivate the Omicron-pseudovirus and bacteria on the surface of different materials including quartz, metal, leather, plastic, and cardboard and the particle size of the water spray did not affect the inactivation effects. This study supplied a disinfection strategy based on plasma-activated air for the inactivation of contaminated pathogenic microorganisms.

Plasma-activated liquids for mitigating biofilms on food and food contact surfaces

Plasma-activated liquids (PALs) are emerging and promising alternatives to traditional decontamination technologies and have evolved as a new technology for applications in food, agriculture, and medicine. Contamination caused by foodborne pathogens and their biofilms has posed challenges and concerns to the food industry in terms of safety and quality. The nature of the food and the food processing environment are major factors that contribute to the growth of various microorganisms, followed by the biofilm characteristics that ensure their survival in severe environmental conditions and against traditional chemical disinfectants. PALs show an efficient impact against microorganisms and their biofilms, with various reactive species (short- and long-lived ones), physiochemical properties, and plasma processing factors playing a crucial role in mitigating biofilms. Moreover, there is potential to improve and optimize disinfection strategies using a combination of PALs with other technologies for the inactivation of biofilms. The overarching aim of this study is to build a better understanding of the parameters that govern the liquid chemistry generated in a liquid exposed to plasma and how these translate into biological effects on biofilms. This review provides a current understanding of PALs-mediated mechanisms of action on biofilms; however, the precise inactivation mechanism is still not clear and is an important part of the research. Implementation of PALs in the food industry could help overcome the disinfection hurdles and can enhance biofilm inactivation efficacy. Future perspectives in this field to expand existing state of the art to seek breakthroughs for scale-up and implementation of PALs technology in the food industry are also discussed.

Plasma-Generated Nitric Oxide Water Mediates Environmentally Transmitted Pathogenic Bacterial Inactivation via Intracellular Nitrosative Stress

Over time, the proportion of resistant bacteria will increase. This is a major concern. Therefore, effective and biocompatible therapeutic strategies against these bacteria are urgently needed. Non-thermal plasma has been exhaustively characterized for its antibacterial activity. This study aims to investigate the inactivation efficiency and mechanisms of plasma-generated nitric oxide water (PG-NOW) on pathogenic water, air, soil, and foodborne Gram-negative and Gram-positive bacteria. Using a colony-forming unit assay, we found that PG-NOW treatment effectively inhibited the growth of bacteria. Moreover, the intracellular nitric oxide (NO) accumulation was evaluated by 4-amino-5-methylamino-2',7'-dichlorofluorescein diacetate (DAF-FM DA) staining. The reduction of viable cells unambiguously indicates the anti-microbial effect of PG-NOW. The soxR and soxS genes are associated with nitrosative stress, and oxyR regulation corresponds to oxidative stress in bacterial cells. To support the nitrosative effect mediated by PG-NOW, we have further assessed the soxRS and oxyR gene expressions after treatment. Accordingly, soxRS expression was enhanced, whereas the oxyR expression was decreased following PG-NOW treatment. The disruption of cell morphology was observed using scanning electron microscopy (SEM) analysis. In conclusion, our findings furnish evidence of an initiation point for the further progress and development of PG-NOW-based antibacterial treatments.

Enhancement of Wheat Seed Germination, Seedling Growth and Nutritional Properties of Wheat Plantlet Juice by Plasma Activated Water

Previous studies have shown the great potential of using plasma-activated water (PAW) on improving agriculture seed germination, however, information on the influence of PAW on crop plantlet juice remains scanty. In this research, the effect of PAW generated by atmosphere pressure Ar-O₂ plasma jet for 1-5 min on wheat seed germination, seedling growth and nutritional properties of wheat plantlet juice was investigated. Results revealed that all PAWs could enhance wheat seed germination and seedling growth in 7 days by improving the germination rate, germination index, fresh weight, dry weight and vigour index, and especially that PAW activated for 3 min (PAW-3) showed the best overall performance. In addition, the application of PAWs enhanced the nutritional properties of wheat plantlet juice from those grown for 14 days by improving total soluble solids, protein content, photosynthetic pigments, total phenolic content, antioxidant activity, enzyme activity, free amino acids and minerals content, and the best enhancement was also observed in PAW-3. It was concluded that PAWs would be an effective technique to enhance the growth and nutritional properties of crop sprouts, which could be served as functional foods in many forms.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s00344-022-10677-3.

The Chemical Biology of NO that Regulates Oncogenic Signaling and Metabolism: NOS2 and Its Role in Inflammatory Disease

Nitric oxide (NO) and the enzyme that synthesizes it, nitric oxide synthase 2 (NOS2), have emerged as key players in inflammation and cancer. Expression of NOS2 in tumors has been correlated both with positive outcomes and with poor prognoses. The chemistry of NO is the major determinate to the biological outcome and the concentration of NO, which can range over five orders of magnitude, is critical in determining which pathways are activated. It is the activation of specific oncogenic and immunological mechanisms that shape the outcome. The kinetics of specific reactions determine the mechanisms of action. In this review, the relevant reactions of NO and related species are discussed with respect to these oncogenic and immunological signals.

Optimization of Plasma-activated Water and Validation of a Potential Surrogate for Salmonella for Future Egg Washing Processes

Plasma-activated water (PAW) is considered a novel sanitizer for the food industry due to the antimicrobial mechanisms exhibited by reactive oxygen and nitrogen species. The plasma operation parameters can affect the chemistry of PAW and can therefore influence its microbial inactivation efficacy. This study statistically optimized the operating conditions of PAW (activation time, distance from nozzle, and volume of water) using response surface methodology. Two optimized conditions of PAW were identified for the inactivation of planktonic cells of the avirulent strain of Salmonella Typhimurium MHM112 providing a minimum reduction of 6.3 log. All three operating parameters significantly affected the physicochemical characteristics (pH, ORP, EC, nitrite, and nitrate) and microbial inactivation efficacy of PAW. Mixing of small batches using the two optimized conditions to obtain larger volumes did not significantly change the microbial inactivation. However, there were significant reductions in nitrite and nitrate concentrations in PAW due to the mixing of batches while the pH and ORP values remained unaffected. The storage of large volumes of PAW for 25 min at 40-46°C, which is the commercial egg washing temperature in the United States, did not significantly impact S. Typhimurium MHM112 inactivation or the physicochemical characteristics of PAW. A validation study using a cocktail of six pathogenic strains of Salmonella revealed no significant differences in inactivation between the avirulent S. Typhimurium MHM112 and the pathogenic strains, suggesting that the avirulent S. Typhimurium MHM112 may serve as a surrogate for sanitation of S. enterica at the optimized conditions of PAW. The results obtained from this study are useful for our long-term goal of evaluating PAW efficacy in surface egg washing to inactivate Salmonella.

Efficacy of plasma activated saline in a co-culture infection control model

Plasma activated liquids have demonstrated antimicrobial effects and receive increasing attention due to the potential to strengthen the armoury of novel approaches against antibiotic resistant bacteria. However, the antibacterial activity and cytotoxic effects of these solutions need to be understood and balanced before exposure to humans. In this study, the antibacterial effects of plasma activated saline (PAS) were tested against Gram negative and positive bacteria, and HaCaT keratinocytes were used for cytotoxicity studies. For the first time, a co-culture model between these bacteria and eukaryotic cells under the influence of PAS has been described. Exposure of saline to plasma resulted in high concentrations of nitrate, hydrogen peroxide and a reduction of pH. PAS caused high antibacterial effects in the co-culture model, accompanied by high cytotoxic effects to the monolayer of mammalian cells. We present evidence and provide a deeper understanding for the hypothesis that upon treatment with PAS, chemical species generated in the liquid mediate high antimicrobial effects in the co-culture setup as well as mitochondrial depolarization and glutathione depletion in HaCaT cells and cell lysis due to acidic pH. In conclusion, PAS retains strong antibacterial effects in a co-culture model, which may have unintended negative biological effects on mammalian cells.

Oxidative lesions and post-treatment viability attenuation of listeria monocytogenes triggered by atmospheric non-thermal plasma

AIMS

The aim of the current study was to investigate the effect of plasma-mediated oxidative stress on the post-treatment viability of Listeria monocytogenes at the physiological and molecular levels.

METHODS AND RESULTS

10⁷  CFU/ml L. monocytogenes in 10 ml phosphate-buffered saline (PBS) was treated with atmospheric non-thermal plasma for 0, 30, 60, 90 and 120 s respectively. Optical diagnostics using optical emission spectroscopy (OES) confirmed that dielectric barrier discharge (DBD) plasma was a significant source of ample exogenous reactive oxygen and nitrogen species (RONS). The development of extracellular main long-lived species was associated with plasma exposure time, accompanied by a massive accumulation of intracellular ROS in L. monocytogenes (p < 0.01). With the exception of virulence genes (hly), most oxidation resistance genes (e.g. sigB, perR, lmo2344, lmo2770 and trxA) and DNA repair gene (recA) were upregulated significantly (p < 0.05). A visible fragmentation in genomic DNA and a decline in the secretion of extracellular proteins and haemolytic activity (p < 0.01) were noticed. The quantitate oxygen consumption rates (OCRs) and extracellular acidification rates (ECARs) confirmed the viability attenuation from the aspect of energy metabolism. Survival assay in a real food system (raw milk) further suggested not only the viability attenuation, but also the resuscitation potential and safety risk of mild plasma-treated cells during post-treatment storage.

CONCLUSION

DBD plasma had the potential to inactivate and attenuate the virulence of L. monocytogenes, and it was recommended that plasma exposure time longer than 120 s was more suitable for attenuating viability and avoiding the recovery possibility of L. monocytogenes in raw milk within 7 days.

SIGNIFICANCE AND IMPACT OF THE STUDY

The current results presented a strategy to inactivate and attenuate the viability of L. monocytogenes, which could serve as a theoretical basis for better application of non-thermal plasma in food in an effort to effectively combat foodborne pathogens.

The Modulatory Effects of Non-Thermal Plasma on Seed’s Morphology, Germination and Genetics—A Review

Non-thermal plasma (NTP) is a novel and promising technique in the agricultural field that has the potential to improve vegetal material by modulating the expression of various genes involved in seed germination, plant immune response to abiotic stress, resistance to pathogens, and growth. Seeds are most frequently treated, in order to improve their ability to growth and evolve, but the whole plant can also be treated for a fast adaptive response to stress factors (heat, cold, pathogens). This review focuses mainly on the application of NTP on seeds. Non-thermal plasma treated seeds present both external and internal changes. The external ones include the alterations of seed coat to improve hydrophilicity and the internal ones refer to interfere with cellular processes that are later visible in metabolic and plant biology modifications. The usage of plasma aims to decrease the usage of fertilizers and pesticides in order to reduce the negative impact on natural ecosystem and to reduce the costs of production.

The inactivation efficacy of plasma-activated acetic acid against Salmonella Typhimurium cells and biofilm

AIM

This study aimed to examine the inactivation efficacy of plasma-activated acetic acid (PAAA) against Salmonella Typhimurium cells and biofilm and elucidate the underlying the chemical inactivation pathway.

METHODS AND RESULTS

PAAA was prepared by discharging plasma to 20 ml of 0.2% (v/v) acetic acid (AA) for 20 min (2.2 kHz and 8.4 kVpp). The count of cells and biofilms decreased by 5.71 log CFU ml^-1 and 4 log CFU/cm² after 10 min of treatment with 0.2% PAAA and 0.4% PAAA compared with control group (without any treatment), respectively. In 0.2% PAAA, the concentrations of hydrogen peroxide (H₂ O₂ ) and nitrate anions were directly proportional to the plasma discharge time, while nitrite anions (NO₂ ^- ) was not detected. However, the pH values of both 0.2% PAAA and plasma-activated water were inversely proportional to the plasma discharge time. Treatment with catalase, L-histidine, D-mannitol, and sodium azide inhibited the antibacterial activity of PAAA.

CONCLUSION

H₂ O₂ , Singlet oxygen, Hydroxyl radical, and NO₂ ^- are involved in the generation and decomposition of peroxynitrous acid generated from PAAA functioned as intermediate agent, which could diffuse through cell membranes of bacteria and induce cell injury.

SIGNIFICANCE AND IMPACT OF STUDY

This study provides the understanding of efficacy and selectivity of PAAA which could be a novel decontamination agent.

Decontamination of Pathogenic and Spoilage Bacteria on Pork and Chicken Meat by Liquid Plasma Immersion

In this research, we aimed to reduce the bacterial loads of Salmonella Enteritidis, Salmonella Typhimurium, Escherichia coli, Campylobacter jejuni, Staphylococcus aureus, and Pseudomonas aeruginosa in pork and chicken meat with skin by applying cold plasma in a liquid state or liquid plasma. The results showed reductions in S. Enteritidis, S. Typhimurium, E. coli, and C. jejuni on the surface of pork and chicken meat after 15 min of liquid plasma treatment on days 0, 3, 7, and 10. However, the efficacy of the reduction in S. aureus was lower after day 3 of the experiment. Moreover, P. aeruginosa could not be inactivated under the same experimental conditions. The microbial decontamination with liquid plasma did not significantly reduce the microbial load, except for C. jejuni, compared with water immersion. When compared with a control group, the pH value and water activity of pork and chicken samples treated with liquid plasma were significantly different (p ≤ 0.05), with a downward trend that was similar to those of the control and water groups. Moreover, the redness (a*) and yellowness (b*) values (CIELAB) of the meat decreased. Although the liquid plasma group resulted in an increase in the lightness (L*) values of the pork samples, these values did not significantly change in the chicken samples. This study demonstrated the efficacy of liquid plasma at reducing S. Enteritidis, S. Typhimurium, E. coli, C. jejuni, and S. aureus on the surface of pork and chicken meat during three days of storage at 4–6 °C with minimal undesirable meat characteristics.

Plasma-Activated Water for Food Safety and Quality: A Review of Recent Developments

Plasma-activated water (PAW) has received a lot of attention lately because of its antibacterial efficacy and eco-friendly nature. Compared to traditional disinfectants, this novel and intriguing option has a high disinfectant capacity while causing little to no modifications to the foodstuffs. Until now, PAW has successfully demonstrated its effectiveness against a broad range of microorganisms on a wide variety of food items. Though the efficacy of PAW in microbial reduction has been extensively reviewed, a relatively significant issue of food quality has been largely overlooked. This review aims to summarize the current studies on the physicochemical characteristics and antimicrobial potential of PAW, with an in-depth focus on food quality and safety. According to recent studies, PAW can be a potential microbial disinfectant that extends the shelf life of various food products, such as meat and fish products, fruits and vegetables, cereal products, etc. However, the efficacy varies with treatment conditions and the food ingredients applied. There is a mixed opinion about the effect of PAW on food quality. Based on the available literature, it can be concluded that there has been no substantial change in the biochemical properties of most of the tested food products. However, some fruits and vegetables had a higher value for the enzyme superoxide dismutase (SOD) after PAW treatment, while only a few demonstrated a decrease in the Thiobarbituric acid reactive substances (TBARS) value. Sensory properties also showed no significant difference, with some exceptions in meat and fish products.

Effect of MoS2 on phenol decomposition in water after high-voltage pulse discharge treatment

Molybdenum disulfide (MoS₂) was added to the system after being treated with high-voltage pulse discharge plasma to improve the degradation efficiency of pollutants and reduce energy consumption. The discharge plasma-treated solution contains hydrogen peroxide and metal iron ions, and MoS₂ addition can cause co-catalytic Fenton reaction. The effects of discharge time, initial pH, phenol concentration, MoS₂ dosage, discharge voltage, and gas type on phenol removal and aqueous H₂O₂ concentration were mainly investigated. Results showed that the addition of MoS₂ after plasma treatment can reduce the plasma treatment time by 70% and maintain or even increase the degradation efficiency of phenol from 40% (after 20 min of discharge plasma) to 92% (after turning off the discharge and dosing with MoS₂ for 30 min). Acidic conditions (pH = 3-4) and oxygen were beneficial to phenol removal. MoS₂ addition greatly improved the catalytic oxidation of discharge plasma. This study provides a promising direction for water treatment based on plasma technology.

Nanoscale plasma-activated aerosol generation for in situ surface pathogen disinfection

Plasma treatment constitutes an efficient method for chemical-free disinfection. A spray-based system for dispensing plasma-activated aerosols onto surfaces would facilitate disinfection of complex and/or hidden surfaces inaccessible to direct line-of-sight (for example, UV) methods. The complexity and size of current plasma generators (for example, plasma jet and cometary plasma systems)-which prohibit portable operation, together with the short plasma lifetimes, necessitate a miniaturized in situ technique in which a source can be simultaneously activated and administered on-demand onto surfaces. Here, we demonstrate this possibility by combining two nanoscale technologies for plasma and aerosol generation into an integrated device that is sufficiently small and lightweight. Plasma is generated on a carpet of zinc oxide nanorods comprising a nanoneedle ensemble, which when raised to a high electric potential, constitutes a massive point charge array with near-singular electric fields to effect atmospheric breakdown. The plasma is then used to activate water transported through an underlying capillary wick, that is subsequently aerosolized under MHz-order surface acoustic waves. We show that the system, besides being amenable to miniaturization and hence integration into a chipscale device, leads to a considerable improvement in plasma-activation over its macroscale cometary discharge predecessor, with up to 20% and 127% higher hydrogen peroxide and nitrite ion concentrations that are respectively generated in the plasma-activated aerosols. This, in turn, leads to a 67% reduction in the disinfection time to achieve 95% bacterial load reduction, therefore demonstrating the potential of the technology as an efficient portable platform for on-demand field-use surface disinfection.

Antimicrobial effects of microwave plasma-activated water with skin protective effect for novel disinfectants in pandemic era

Skin antiseptics have important implications for public health and medicine. Although conventional antiseptics have considerable antimicrobial activity, skin toxicity and the development of resistance are common problems. Plasma-treated water has sterilization and tissue-regenerative effects. Therefore, the aim of this study was to identify whether plasma-activated water (PAW) manufactured by our microwave plasma system can be used as a novel antiseptic solution for skin protection. PAW was produced by dissolving reactive nitrogen oxide gas using microwave plasma in deionized water. The antibacterial effects of PAW against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus, and Salmonella typhimurium and effective concentrations were investigated by a solid agar plate assay. The factors mediating the effects of PAW were evaluated by the addition of reactive species scavengers. Cytotoxicity and cell viability assays were performed to examine the protective effect of PAW on normal skin cells. PAW exhibited excellent sterilization and no toxicity in normal skin cells. Experiments also confirmed the potential of PAW as a sanitizer for SARS-CoV-2. Our findings support the use of PAW as an effective skin disinfectant with good safety in the current situation of a global pandemic.

Applications of Plasma-Activated Water in Dentistry: A Review

The activation of water by non-thermal plasma creates a liquid with active constituents referred to as plasma-activated water (PAW). Due to its active constituents, PAW may play an important role in different fields, such as agriculture, the food industry and healthcare. Plasma liquid technology has received attention in recent years due to its versatility and good potential, mainly focused on different health care purposes. This interest has extended to dentistry, since the use of a plasma–liquid technology could bring clinical advantages, compared to direct application of non-thermal atmospheric pressure plasmas (NTAPPs). The aim of this paper is to discuss the applicability of PAW in different areas of dentistry, according to the published literature about NTAPPs and plasma–liquid technology. The direct and indirect application of NTAPPs are presented in the introduction. Posteriorly, the main reactors for generating PAW and its active constituents with a role in biomedical applications are specified, followed by a section that discusses, in detail, the use of PAW as a tool for different oral diseases.

Evaluation of the Storage Stability and Quality Properties of Fresh Noodles Mixed with Plasma-Activated Water

Enhancing the quality retention of fresh noodles remains challenging. In this study, we investigated the effect of dough mixing with plasma-activated water (PAW) of different activation times on the storage stability and quality characteristics of fresh noodles. It was found that the total plate count in the fresh noodles prepared by PAW (PAWN) showed no obvious inhibition during storage at 25 °C, but could be significantly reduced at 4 °C as compared with the control. The decrease in L* value and pH of the PAWN was significantly retarded during storage, indicating an enhanced storage stability. The stability time of dough mixed with PAW could be significantly improved. PAW treatment decreased the viscosity properties and setback value of starch, while enhancing the interaction of water and non-water components in fresh noodles. In addition, dynamic polymerization and depolymerization of proteins were detected in Size-Exclusion High-Performance Liquid Chromatography (SE-HPLC) profiles of PAWN. The hardness and adhesiveness of the cooked noodles decreased, while the springiness significantly increased. These results implied the potential of PAW in improving the storage stability and quality of fresh noodles.

Cold Plasma as a Potential Activator of Plant Biostimulants

Agriculture has become a sector with a huge impact on the natural environment. The interest of agriculture in the category of innovative bio-stimulants is due to the intensive search for preparations based on natural substances. This is not possible without developing and implementing innovative technologies, e.g., cold plasma, along with innovative technologies supporting farmers. Therefore, given the need to prevent environmental damage caused by intensive agriculture, plant production and protection must be targeted at merging the stimulation of crop growth and the elimination of threats to humans and the environment. The analysis of how cold plasma can influence the production of organic bio-stimulants seems to be an unavoidable step in future approaches to this topic. Since allelopathic plants represent a source of many chemical compounds promoting crop growth and development, the coupling of biologically-active compound extraction with plasma activation of allelopathic extracts has interesting potential in offering the most modern alternative to conventional agriculture. However, its implementation in practice will only be feasible after a comprehensive and thoughtful investigation of the mechanisms behind crops’ response to such bio-stimulants.

Interactions between pH, reactive species, and cells in plasma-activated water can remove algae

Lightning strikes cause nitrogen to dissolve in water and form reactive nitrogen and oxygen species, which form natural fertilizers that can be absorbed through plant roots. Such processes during rainstorm events can be simulated by applying plasma to a solution. Plasma-activated water (PAW) has great potential as a source of various dissolved reactive chemical species. Different mixtures of species are produced using different solution compositions. Here, basil seeds were grown in PAW to prevent blooms of Chlorella vulgaris and ion chromatography and UV-vis spectroscopy were used to quantify reactive ions. NO₂⁻, NO₃⁻, and H₂O₂ were found to be key to the antialgal effect. Secondary reactive ions such as peroxynitrite (ONOO⁻, ONOOH) were also involved. The antialgal effect was strongly related to the pH around the algal cells. Acidification was predominantly caused by the generation of NO₂⁻ and H₂O₂. After two weeks monitoring basil growth, the antifungal properties were preserved, few reactive oxygen species formed in the plasma zone, and only reactive nitrogen species were transformed into reactive peroxynitrite ions. The pH around the cells was determined using an iridium oxide microelectrode. The PAW antialgal mechanism depended on acidic conditions (pH 2.2, at which peroxynitrite can be generated) under which ONOOH penetrated the algal cell membranes, destroying the cells and preventing growth. This practical and sustainable PAW process allows a surprising amount of fertilizer to be generated with an antialgal effect that could be used in various eco-friendly agricultural processes under ambient conditions.

PAW is effective in inactivating microorganisms. We have measured a local pH to reveal the mechanism of algicidal effect in PAW. This is because protons pumped from the cell generate peroxynitrite around the cell to generate an acidic region.

Effect of Plasma-Activated Solution Treatment on Cell Biology of Staphylococcus aureus and Quality of Fresh Lettuces

This study aimed to investigate effects of plasma-activated solution (PAS) on the cell biology of Staphylococcus aureus and qualities of fresh lettuce leaves. PAS was prepared by dielectric barrier discharge plasma and incubated with S. aureus for 10–30 min or with lettuces for 10 min. Effects on cell biology were evaluated with microscopic images, cell integrity, and chemical modification of cellular components. Effects on lettuce quality were estimated with the viable microbial counts, color, contents of vitamin C and chlorophyll, and surface integrity. PAS reduced S. aureus population by 4.95-log and resulted in increased cell membrane leakage. It also resulted in increased contents of reactive oxygen species in cells, C=O bonds in peptidoglycan, and 8-hydroxydeoxyguanosine content in cellular DNA, and reduced ratios of unsaturated/saturated fatty acids in the cell membrane. PAS treatment reduced bacterial load on fresh lettuce and had no negative effects on the quality. Data suggest that PAS can be used for the disinfection of ready-to-eat fresh vegetables.

Plasma-Activated Water Triggers Rapid and Sustained Cytosolic Ca2+ Elevations in Arabidopsis thaliana

Increasing evidence indicates that water activated by plasma discharge, termed as plasma-activated water (PAW), can promote plant growth and enhance plant defence responses. Nevertheless, the signalling pathways activated in plants in response to PAW are still largely unknown. In this work, we analysed the potential involvement of calcium as an intracellular messenger in the transduction of PAW by plants. To this aim, Arabidopsis thaliana (Arabidopsis) seedlings stably expressing the bioluminescent Ca²⁺ reporter aequorin in the cytosol were challenged with PAW generated by a plasma torch. Ca²⁺ measurement assays demonstrated the induction by PAW of rapid and sustained cytosolic Ca²⁺ elevations in Arabidopsis seedlings. The dynamics of the recorded Ca²⁺ signals were found to depend upon different parameters, such as the operational conditions of the torch, PAW storage, and dilution. The separate administration of nitrate, nitrite, and hydrogen peroxide at the same doses as those measured in the PAW did not trigger any detectable Ca²⁺ changes, suggesting that the unique mixture of different reactive chemical species contained in the PAW is responsible for the specific Ca²⁺ signatures. Unveiling the signalling mechanisms underlying plant perception of PAW may allow to finely tune its generation for applications in agriculture, with potential advantages in the perspective of a more sustainable agriculture.

Non-thermal Plasma Treatment of ESKAPE Pathogens: A Review

The acronym ESKAPE refers to a group of bacteria consisting of Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. They are important in human medicine as pathogens that show increasing resistance to commonly used antibiotics; thus, the search for new effective bactericidal agents is still topical. One of the possible alternatives is the use of non-thermal plasma (NTP), a partially ionized gas with the energy stored particularly in the free electrons, which has antimicrobial and anti-biofilm effects. Its mechanism of action includes the formation of pores in the bacterial membranes; therefore, resistance toward it is not developed. This paper focuses on the current overview of literature describing the use of NTP as a new promising tool against ESKAPE bacteria, both in planktonic and biofilm forms. Thus, it points to the fact that NTP treatment can be used for the decontamination of different types of liquids, medical materials, and devices or even surfaces used in various industries. In summary, the use of diverse experimental setups leads to very different efficiencies in inactivation. However, Gram-positive bacteria appear less susceptible compared to Gram-negative ones, in general.

Toxicity Assessment of Long-Term Exposure to Non-Thermal Plasma Activated Water in Mice

Non-thermal plasma activated water (PAW) has recently emerged as a powerful antimicrobial agent. Despite numerous potential bio-medical applications, studies concerning toxicity in live animals, especially after long-term exposure, are scarce. Our study aimed to assess the effects of long-term watering with PAW on the health of CD1 mice. PAW was prepared from distilled water with a GlidArc reactor according to a previously published protocol. The pH was 2.78. The mice received PAW (experimental group) or tap water (control group) daily for 90 days as the sole water source. After 90 days, the following investigations were performed on the euthanatized animals: gross necropsy, teeth mineral composition, histopathology, immunohistochemistry, hematology, blood biochemistry, methemoglobin level and cytokine profile. Mice tolerated PAW very well and no adverse effects were observed during the entire period of the experiment. Histopathological examination of the organs and tissues did not reveal any structural changes. Moreover, the expression of proliferation markers PCNA and Ki67 has not been identified in the epithelium of the upper digestive tract, indicating the absence of any pre- or neoplastic transformations. The results of our study demonstrated that long-term exposure to PAW caused no toxic effects and could be used as oral antiseptic solution in dental medicine.

Plasma-Activated Saline Promotes Antibiotic Treatment of Systemic Methicillin-Resistant Staphylococcus aureus Infection

Systemic infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are life-threatening due to their strong multidrug resistance, especially since the biofilms formed by MRSA are more difficult to inactivate by antibiotics, causing long term recurrence of infection. Plasma-activated saline (PAS), a derived form of cold atmospheric-pressure plasma, can effectively inactivate bacteria and cancer cells and has been applied to sterilization and cancer treatment. Previous studies have demonstrated that the pretreatment of MRSA with PAS could promote the action of antibiotics. Here, the PAS was used as an antibiotic adjuvant to promote the inactivation of MRSA biofilms by rifampicin and vancomycin, and the combined treatment reduced approximately 6.0-log₁₀ MRSA cells in biofilms. The plasma-activated saline and rifampicin synergistically and effectively reduced the systemic infection in the murine model. The histochemical analysis and the blood hematological and biochemical test demonstrated that the combined treatment with plasma-activated saline and rifampicin improved the blood hematological and biochemical parameters of infected mice by reducing the infection. Therefore, PAS based on plasma technology represents a new strategy for the treatment of infectious disease caused by multidrug-resistant bacteria and alleviating antibiotic resistance.