Antibacterial activity and a membrane damage mechanism of plasma-activated water against Pseudomonas deceptionensis CM2

Mechanisms underlying the potent antimicrobial effects of plasma-activated seawater (PASW) on fish spoilage bacterium Shewanella putrefaciens

Plasma-activated seawater (PASW) presents a promising approach for marine fish preservation, yet its antimicrobial efficacy and mechanisms remain unclear. This study found that PASW exhibits superior bactericidal properties against the fish spoilage bacterium Shewanella putrefaciens compared to plasma-activated water (PAW), and increased effectiveness in preserving fish fillets. To clarify the mechanisms, a detailed investigation was conducted, including the generation of reactive oxygen/nitrogen species (ROS/RNS) and active halogen species in PASW, and their antimicrobial efficacy. Findings showed greater nitrite and hydrogen peroxide production in PASW relative to PAW, as well as the conversion of chloride/bromide ions into active species, which collectively enhanced PASW's antimicrobial activity. The synergistic action of ROS/RNS and active chlorine/bromine species in PASW promoted the generation of intracellular ROS, causing increased membrane damage, redox imbalance, and consequently higher bacterial mortality. This study enhances our understanding of PASW's antimicrobial effects and highlights its potential applications in the seafood industry.

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.

Differential mechanism between Listeria monocytogenes strains with different virulence contaminating ready-to-eat sausages during the simulated gastrointestinal tract

Listeria monocytogenes exhibits varying levels of pathogenicity when entering the host through contaminated food. However, little is known regarding the stress response and environmental tolerance mechanism of different virulence strains to host gastrointestinal (GI) stimuli. This study analyzed the differences in the survival and genes of stress responses among two strains of L. monocytogenes 10403S (serotype 1/2a, highly virulent strain) and M7 (serotype 4a, low-virulence strain) during simulated gastrointestinal digestion. The results indicated that L. monocytogenes 10403S showed greater acid and bile salt tolerance than L. monocytogenes M7, with higher survival rates and less cell deformation and cell membrane permeability during the in vitro digestion. KEGG analysis of the transcriptomes indicated that L. monocytogenes 10403S displayed significant activity in amino acid metabolism, such as glutamate and arginine, associated with acid tolerance. Additionally, L. monocytogenes 10403S demonstrated a higher efficacy in promoting activities that preserve bacterial cell membrane integrity and facilitate flagellar protein synthesis. These findings will contribute valuable practical insights into the tolerance distinctions among different virulence strains of L. monocytogenes in the GI environment.

Antimicrobial Activity and Mechanisms of Punicalagin against Vibrio parahaemolyticus

This study sought to explore the antimicrobial activity of punicalagin against V. parahaemolyticus and its potential modes of action. V. parahaemolyticus ATCC 17802 and RIMD 2210633Sm were exposed to punicalagin, and the energy production, membrane potential, and envelope permeability, as well as the interaction with cell biomolecules, were measured using a variety of fluorescent probes combined with electrophoresis and Raman spectroscopy. Punicalagin treatment disrupted the envelope integrity and induced a decrease in intracellular ATP and pH. The uptake of 1-N-phenyl-naphtylamine (NPN) demonstrated that punicalagin weakened the outer membrane. Punicalagin damaged the cytoplasmic membrane, as indicated by the membrane depolarization and the leakage of intracellular potassium ions, proteins, and nucleic acids. Electronic microscopy observation visualized the cell damage caused by punicalagin. Further, gel electrophoresis coupled with the Raman spectrum assay revealed that punicalagin affected the protein expression of V. parahaemolyticus, and there was no effect on the integrity of genomic DNA. Therefore, the cell envelope and proteins of V. parahaemolyticus were the assailable targets of punicalagin treatment. These findings suggested that punicalagin may be promising as a natural bacteriostatic agent to control the growth of V. parahaemolyticus.

Natural bioactive compounds targeting DNA methyltransferase enzymes in cancer: Mechanisms insights and efficiencies

The regulation of gene expression is fundamental to health and life and is essentially carried out at the promoter region of the DNA of each gene. Depending on the molecular context, this region may be accessible or non-accessible (possibility of integration of RNA polymerase or not at this region). Among enzymes that control this process, DNA methyltransferase enzymes (DNMTs), are responsible for DNA demethylation at the CpG islands, particularly at the promoter regions, to regulate transcription. The aberrant activity of these enzymes, i.e. their abnormal expression or activity, can result in the repression or overactivation of gene expression. Consequently, this can generate cellular dysregulation leading to instability and tumor development. Several reports highlighted the involvement of DNMTs in human cancers. The inhibition or activation of DNMTs is a promising therapeutic approach in many human cancers. In the present work, we provide a comprehensive and critical summary of natural bioactive molecules as primary inhibitors of DNMTs in human cancers. The active compounds hold the potential to be developed as anti-cancer epidrugs targeting DNMTs.

Bactericidal efficacy of plasma-activated water against Vibrio parahaemolyticus on Litopenaeus vannamei

In this study, the antimicrobial mechanism of plasma-activated water (PAW) against Vibrio parahaemolyticus and the effectiveness of PAW in artificially contaminated Litopenaeus vannamei were investigated. The results demonstrated a significant reduction (p < 0.05) in viable counts of V. parahaemolyticus with increasing plasma discharge time (5, 10, 20, and 30 min) and PAW immersion time (3, 5, 10, 20, and 30 s). Specifically, the count of V. parahaemolyticus decreased by 2.1, 2.7, 3.3, and 4.4 log CFU/mL after exposed to PAW 5, PAW 10, PAW 20, and PAW 30 for 30 s, respectively. Significant cell surface wrinkling, accompanied by notable nucleic acid and protein leakage were observed after treatment with PAW. The permeability of the inner and outer cell membranes was significantly increased (p < 0.05), along with an increase in electrical conductivity (p < 0.05). The reactive oxygen species (ROS) within V. parahaemolyticus cells were significantly increased (p < 0.05), while superoxide dismutase (SOD) activity, and the relative expression of the ompW, emrD, and luxS genes were significantly decreased (p < 0.05). A reduction number of 1.3, 1.8, 2.1, and 2.2 log CFU/g of V. parahaemolyticus in artificially contaminated L. vannamei was obtained with PAW for 5 min. The study elucidated that PAW could destroy cell membranes, leading to cell death. The findings would strengthen strategies for V. parahaemolyticus control and provide a potential application of PAW for preserving aquatic products.

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.

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.

Chestnut Shell Polyphenols Inhibit the Growth of Three Food-Spoilage Bacteria by Regulating Key Enzymes of Metabolism

The microbial contamination of food poses a threat to human health. Chestnut shells, which are byproducts of chestnut processing, contain polyphenols that exert various physiological effects, and thus have the potential to be used in food preservation. This study investigates the bacteriostatic effect and mechanism(s) of the action of chestnut shell polyphenols (CSPs) on three food-spoilage bacteria, namely Bacillus subtilis, Pseudomonas fragi, and Escherichia coli. To this end, the effect of CSPs on the ultrastructure of each bacterium was determined using scanning electron microscopy and transmission electron microscopy. Moreover, gene expression was analyzed using RT-qPCR. Subsequent molecular docking analysis was employed to elucidate the mechanism of action employed by CSPs via the inhibition of key enzymes. Ultrastructure analysis showed that CSPs damaged the bacterial cell wall and increased permeability. At 0.313 mg/mL, CSPs significantly increased the activity of alkaline phosphatase and lactate dehydrogenase, as well as protein leakage (p < 0.05), whereas the activity of the tricarboxylic acid (TCA) cycle enzymes, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, were inhibited (p < 0.05). The expression levels of the TCA-related genes gltA, icd, sucA, atpA, citA, odhA, IS178_RS16090, and IS178_RS16290 are also significantly downregulated by CSP treatment (p < 0.05). Moreover, CSPs inhibit respiration and energy metabolism, including ATPase activity and adenosine triphosphate (ATP) synthesis (p < 0.05). Molecular docking determined that proanthocyanidins B1 and C1, the main components of CSPs, are responsible for the antibacterial activity. Therefore, as natural antibacterial substances, CSPs have considerable potential for development and application as natural food preservatives.

Antibacterial activity and mechanism of cinnamon essential oil nanoemulsion against Pseudomonas deceptionensis CM2

This work aimed to evaluate the antibacterial activity and mechanism of cinnamon essential oil nanoemulsion (CON) against Pseudomonas deceptionensis CM2. The results revealed that CON could effectively inhibit the proliferation of P. deceptionensis CM2 cells in a time- and concentration-dependent manner. After 4 h of incubation with CON at the minimum inhibitory concentration (0.125 mg/mL), the relative fluorescence intensity of propidium iodide and 1-N-phenylnapthylamine (NPN) was increased by 32.0% and 351.4%, respectively. The membrane permeability of P. deceptionensis CM2 cells was significantly disrupted after CON treatment, resulting in the leakage of intracellular substances (such as proteins and electrolytes). CON also caused significant increases in the DiBAC4(3) fluorescence intensity of P. deceptionensis CM2 cells. These results demonstrate that CON induced inactivation of P. deceptionensis CM2 by destroying the integrity and function of bacterial membrane. A higher level of intracellular reactive oxygen species (ROS) was observed in CON-treated cells (p < 0.05), compared with control cells. Moreover, the addition of glutathione to the growth medium remarkably decreased the antimicrobial activity of CON against P. deceptionensis CM2, further confirming that oxidative stress played an important role in the antimicrobial activity of CON. Overall, CON may exhibit antibacterial effects by causing damage to the bacterial membranes and oxidative stress.

Effects of Plasma-Activated Water Treatment on the Inactivation of Microorganisms Present on Cherry Tomatoes and in Used Wash Solution

Herein, we investigated the potential of plasma-activated water (PAW) as a wash solution for the microbial decontamination of cherry tomatoes. We analyzed the efficacy of PAW as a bactericidal agent based on reactive species and pH. Immersion for 5 min in PAW15 (generated via plasma activation for 15 min) was determined as optimal for microbial decontamination of fresh produce. The decontamination efficacy of PAW15 exceeded those of mimic solutions with equivalent reactive species concentrations and pH (3.0 vs. 1.7 log reduction), suggesting that the entire range of plasma-derived reactive species participates in decontamination rather than a few reactive species. PAW15-washing treatment achieved reductions of 6.89 ± 0.36, 7.49 ± 0.40, and 5.60 ± 0.05 log₁₀ CFU/g in the counts of Bacillus cereus, Salmonella sp., and Escherichia coli O157:H7, respectively, inoculated on the surface of cherry tomatoes, with none of these strains detected in the wash solution. During 6 days of 25 °C storage post-washing, the counts of aerobic bacteria, yeasts, and molds were below the detection limit. However, PAW15 did not significantly affect the viability of RAW264.7 cells. These results demonstrate that PAW effectively inactivates microbes and foodborne pathogens on the surface of cherry tomatoes and in the wash solution. Thus, PAW could be used as an alternative wash solution in the fresh produce industry without cross-contamination during washing and environmental contamination by foodborne pathogens or potential risks to human health.

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.

Atmospheric cold plasma: A potential technology to control Shewanella putrefaciens in stored shrimp

This work aimed to investigate the inactivation mechanism of atmospheric cold plasma (ACP) against Shewanella putrefaciens both in PBS and sterile shrimp juice (SSJ). Reductions in cell density, cell viability, and biofilm formation activity were observed after ACP treatment. ACP cyclical treatment (1 min, 5 times) was more efficient than a one-time treatment (5 min, 1 time). After ACP cyclical treatment, the cell counts and cell viability of S. putrefaciens in PBS were decreased by 3.41 log CFU/mL and 85.30 %, respectively. As for SSJ group, the antibacterial efficiency of ACP declined, but the antibacterial effect of ACP cyclical treatment was still stronger than that of ACP one-time treatment. The biofilm formation activity of S. putrefaciens in PBS was almost completely inhibited, while it gradually returned to normal level with the prolonged of storage time for the SSJ counterpart. The rapid decrease in AKP activity after ACP treatment indicated the damage to cell wall integrity, which was also demonstrated by TEM. In addition, cell membrane and DNA damage of the strain also occurred after ACP treatment. The ROS fluorescence intensity in PBS was higher for the one-time treatment group, while the cyclical treatment group exhibited higher and more stable ozone levels. It was also detected that the total nitric oxide concentration in bacterial suspension depended on the dose of ACP treatment time. ACP treatment (35 kV) for 5 min, especially cyclical treatment, displayed its antibacterial properties on packaged shrimp contaminated with high concentration of S. putrefaciens. ACP cyclical treatment reduced surface bacterial counts of whole shrimps by 0.52 log CFU/mL, while ACP one-time treatment only achieved a decrease of 0.18 log CFU/mL. Therefore, ACP treatment could be considered as a potential alternative to enhance microbial control in food processing.

Using TRIS-Buffered Plasma-Activated Water to Reduce Pathogenic Microorganisms on Poultry Carcasses with Evaluation of Physicochemical and Sensory Parameters

Foodborne diseases are mainly caused by the contamination of meat or meat products with pathogenic microorganisms. In this study, we first investigated the in vitro application of TRIS-buffered plasma-activated water (Tb-PAW) on Campylobacter (C.) jejuni and Escherichia (E.) coli, with a reduction of approx. 4.20 ± 0.68 and 5.12 ± 0.46 log₁₀ CFU/mL. Furthermore, chicken and duck thighs (inoculated with C. jejuni or E. coli) and breasts (with natural microflora) with skin were sprayed with Tb-PAW. Samples were packed under a modified atmosphere and stored at 4 °C for 0, 7, and 14 days. The Tb-PAW could reduce C. jejuni on days 7 and 14 (chicken) and E. coli on day 14 (duck) significantly. In chicken, there were no significant differences in sensory, pH-value, color, and antioxidant activity, but %OxyMb levels decreased, whereas %MetMb and %DeoMb increased. In duck, we observed slight differences in pH-value, color, and myoglobin redox forms for the Tb-PAW, which were not perceived by the sensory test persons. With only slight differences in product quality, its application as a spray treatment may be a useful method to reduce C. jejuni and E. coli on chicken and duck carcasses.

Inactivation of Listeria monocytogenes through the synergistic interaction between plasma-activated water and organic acid

This study observed that when plasma-activated water (PAW) was combined with organic acid, it showed a synergistic inactivation effect on Listeria monocytogenes, which is highly resistant to PAW. When comparing various organic acids, lactic acid (LA) showed the greatest synergistic effect, followed by malic acid (MA), citric acid (CA), and acetic acid (AA), whereas propionic acid (PA) did not show a synergistic effect. Organic acid lowered the activity of ROS defense enzymes (catalase, superoxide dismutase) by reducing intracellular pH (pH_i), which induced the increase in the accumulation of ROS of PAW within the cell. In the end, the synergistic inactivation effect appeared as the increased occurrence of oxidative damage when organic acid was combined as a series of preceding causes. In this case, LA with the greatest ability to lower the pH induced the greatest synergistic effect, suggesting that LA is the best candidate to be combined with PAW. As a result of observing changes in inactivation activity for L. monocytogenes of PAW combined with 1.0% LA while storing at - 80, -20, 4, 25, & 37 °C for 30 days, respectively, it was confirmed that the lower the temperature, the lower the activity loss during the storage period, and that it had an activity of 3.72 log reduction based on 10 min treatment when stored at - 80 °C for 30 days. Application of PAW combined with 1.0% LA stored at - 80 °C for 30 days to mackerel inoculated with L. monocytogenes in ice form resulted in a decrease of 4.53 log after 120 min treatment, without changing the quality of mackerel. These results suggest that combining LA with PAW can be an effective control strategy for L. monocytogenes with high resistance to PAW, and can be effectively utilized, even in ice form.

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.

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.

Application of Pinhole Plasma Jet Activated Water against Escherichia coli, Colletotrichum gloeosporioides, and Decontamination of Pesticide Residues on Chili (Capsicum annuum L.)

Plasma activated water (PAW) generated from pinhole plasma jet using gas mixtures of argon (Ar) and 2% oxygen (O2) was evaluated for pesticide degradation and microorganism decontamination (i.e., Escherichia coli and Colletotrichum gloeosporioides) in chili (Capsicum annuum L.). A flow rate of 10 L/min produced the highest concentration of hydrogen peroxide (H2O2) at 369 mg/L. Results showed that PAW treatment for 30 min and 60 min effectively degrades carbendazim and chlorpyrifos by about 57% and 54% in solution, respectively. In chili, carbendazim and chlorpyrifos were also decreased, to a major extent, by 80% and 65% after PAW treatment for 30 min and 60 min, respectively. E. coli populations were reduced by 1.18 Log CFU/mL and 2.8 Log CFU/g with PAW treatment for 60 min in suspension and chili, respectively. Moreover, 100% of inhibition of fungal spore germination was achieved with PAW treatment. Additionally, PAW treatment demonstrated significantly higher efficiency (p < 0.05) in controlling Anthracnose in chili by about 83% compared to other treatments.

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.

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.

Recent trends and technological development in plasma as an emerging and promising technology for food biosystems

The rising need for wholesome, fresh, safe and “minimally-processed” foods has led to pioneering research activities in the emerging non-thermal technology of food processing. Cold plasma is such an innovative and promising technology that offers several potential applications in the food industry. It uses the highly reactive, energetic and charged gas molecules and species to decontaminate the food and package surfaces and preserve the foods without causing thermal damage to the nutritional and quality attributes of food. Cold plasma technology showed promising results about the inactivation of pathogens in the food industry without affecting the food quality. It is highly effective for surface decontamination of fruits and vegetables, but extensive research is required before its commercial utilization. Recent patents are focused on the applications of cold plasma in food processing and preservation. However, further studies are strongly needed to scale up this technology for future commercialization and understand plasma physics for getting better results and expand the applications and benefits. This review summarizes the emerging trends of cold plasma along with its recent applications in the food industry to extend shelf life and improve the quality of food. It also gives an overview of plasma generation and principles including mechanism of action. Further, the patents based on cold plasma technology have also been highlighted comprehensively for the first time.

Rheological Properties of Wheat Flour Modified by Plasma-Activated Water and Heat Moisture Treatment and in vitro Digestibility of Steamed Bread

The study investigated the effects of plasma-activated water (PAW) and heat moisture treatment (HMT) on the rheological properties of wheat flour and the in vitro digestibility of steamed bread partially replaced by the modified wheat flour. After HMT, the gelatinization temperature of wheat flour increased and the gelatinization enthalpy reduced. The solubility and swelling power of wheat flour increased after the heat-moisture treatment. The solubility of modified flour after PAW-HMT treatment was lower than that of distilled water (DW)-HMT at the same temperature. The wheat flour with HMT had higher storage modulus (G') and loss modulus (G"), and had better ductility and deformability. Common wheat flour was partially replaced by modified flour to make steamed bread. The results indicated that the volume, height, diameter and specific volume of steamed bread were significantly decreased with the addition of HMT flour. However, the hardness, viscosity and chewiness increased significantly. The resistant starch content of steamed bread with the modified wheat flour increased. The results provide new insights for the development of new functional steamed bread.

Chitosan-grafted-phenolic acid copolymers against Shewanella putrefaciens by disrupting the permeability of cell membrane

Chitosan (CS) is a kind of high molecular polymer with antibacterial properties. A copolymer with high bacteriostatic activity can be formed by grafting phenolic acid compounds into the chitosan molecular chain, which can inhibit the growth of dominant spoilage bacteria in aquatic products. The study aimed to investigate the antibacterial effect and mechanism of chitosan-grafted-phenolic acid copolymers on Shewanella putrefaciens (S. putrefaciens). CS-grafted-protocatechuic acid (CS-g-PA) and CS-grafted-gallic acid (CS-g-GA) were attained by EDC/NHS coupling reaction. The antibacterial tests indicated that CS-g-PA and CS-g-GA had the same minimum inhibitory concentration (MIC) (1.25 mg/mL) and minimum bactericidal concentration (MBC) (5.0 mg/mL) against S. putrefaciens. According to the change trend of growth curve, the growth of S. putrefaciens was significantly restrained under 2MIC graft copolymers (P < 0.05). Moreover, the increment of alkaline phosphatase (AKPase) activity and electrical conductivity demonstrated that the cell wall and membrane permeability of S. putrefaciens were damaged respectively. In addition, the increase of lactate dehydrogenase (LDHase) activity, protein and nucleic acid absorbance and the decrease of adenosine triphosphatase (ATPase) activity suggested that the cell membrane was incomplete and poor fluidity. The irregular shape of bacteria and the outflow of intercellular contents were also observed from scanning electron microscope (SEM). The above results manifested a great potential of CS-g-PA and CS-g-GA for use as food preservatives to aquatic products.

Bactericidal efficacy of non-thermal plasma activation against Aeromonas hydrophila and immunological responses of koi (Cyprinus carpio haematopterus)

In the aquaculture industry, an efficient and safe water purification system is important to prevent mass mortality by virulent pathogens. As extensive use of traditional methods (e.g.: povidone-iodine, ozone, ultraviolet irradiation, formalin, and chlorine dioxide) have adverse effects on cultured fish, an appropriate and alternative water purification method is vital for the sustainability of the industry. Non-thermal plasma technology has been successfully used for various biomedical purposes (e.g: food sterilization, medical device disinfection, wound healing, cancer therapy, etc.) and has great potential to be used as a sterilizing system. However, few studies have been conducted on its usefulness in the aquaculture industry. In this study, we investigated the bactericidal efficacy of plasma-activated water induced by non-thermal plasma and its histopathological as well as immunological adverse effects on koi. A highly virulent Aeromonas hydrophila SNU HS7, which caused massive mortality of koi, was used for this study. Non-thermal plasma was applied for 10 min to the fish tanks with 1.2 × 10⁹ CFU/mL SNU HS7 using PLMB-20 system to confirm the sterilization efficacy and to observe the survival and immunological reaction of koi for 14 days. As a result, gross pathological, histopathological, and immunological investigations did not reveal any significant adverse effects in fish as compared to the control groups. To the best of our knowledge, this is the first study showing that non-thermal plasma can be used for sterilization of rearing water without giving significant physiological damage to the fish, even under the assumption of extreme situations. As plasma can effectively sterilize not only bacteria but also other unknown pathogens, the results of this study are showing a promising future in purifying water in aquaculture practice.

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.

Inhibition of corrosion causing Pseudomonas aeruginosa using plasma-activated water

AIMS

The cost of Microbiologically Influenced Corrosion (MIC) significantly affects a wide range of sectors. This study aims to assess the efficiency of a novel technology based on the use of plasma-activated water (PAW) in inhibiting corrosion caused by bacteria.

METHODS AND RESULTS

This study evaluated the effectiveness of PAW, produced by a plasma bubble reactor, in reducing corrosion causing Pseudomonas aeruginosa planktonic cells in tap water and biofilms were grown onto stainless steel (SS) coupons. Planktonic cells and biofilms were treated with PAW at different discharge frequencies (500-1500 Hz) and exposure times (0-20 min). P. aeruginosa cells in tap water were significantly reduced after treatment, with higher exposure times and discharge frequencies achieving higher reductions. Also, PAW treatment led to a gradual reduction for young and mature biofilms, achieving >4-Log reductions after 20 min. Results were also used to develop two predictive inactivation models.

CONCLUSIONS

This work presents evidence that PAW can be used to inactivate both planktonic cells and biofilms of P. aeruginosa. Experimental and theoretical results also demonstrate that reduction is dependent on discharge frequency and exposure time.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work demonstrates the potential of using PAW as means to control MIC.

Effect of Plasma-Activated Water on Shewanella putrefaciens Population Growth and Quality of Yellow River Carp (Cyprinus carpio) Fillets

ABSTRACT

Plasma-activated water (PAW) is a new sanitizer that has received considerable attention for application in food industries. This research aimed to evaluate the effect of PAW on the inactivation of Shewanella putrefaciens and quality attributes of Yellow River carp (Cyprinus carpio) fillets. The carp fillet samples were immersed in sterile deionized water (SDW) or SDW activated by plasma discharge for 120 s (PAW120) for 1.5, 3.0, 4.5, or 6.0 min. After being treated by PAW120 for 6 min, the population of S. putrefaciens on carp fillets was significantly (P < 0.05) decreased by 1.03 log CFU/g. Compared with SDW-treated samples, the L* value of PAW120-treated carp fillets was increased and the a* value was decreased after PAW120 treatment, whereas there was no significant (P > 0.05) difference in the b* value. Compared with SDW, PAW120 caused no significant (P > 0.05) changes in sensory properties and texture attributes of carp fillets including hardness, springiness, gumminess, and cohesiveness. However, 6-min PAW120 treatment caused a significant increase in the lipid oxidation level and a decrease in the pH value of the carp fillets. This work provides a basis for the potential application of PAW in the preservation of aquatic products.

HIGHLIGHTS

Influence of non-thermal plasma reactor geometry and plasma gas on the inactivation of Escherichia coli in water

The inactivation of bacteria Escherichia coli (E. coli) by non-thermal plasma (NTP) was investigated using argon, air and 1:1 mixture of air/Ar as plasma gas on five different reactors. The experiments were carried out in triplicate in each reactor, using 60 mL of distilled water pre-inoculated with E.coli. The physical-chemical analysis of pH, conductivity, nitrite, nitrate and temperature were performed soon after of 10 min of NTP treatment. The microbiological analysis of E. coli inactivation was performed using 100 μL samples withdrawn from the plasma reactor after 10 min and compared with the positive and negative control test results. The best performance were achieved whit the NTP reactors working with the upper electrode in the gas phase using 1:1 air/Ar and air as plasma gas. The results are linked with the E. coli inactivation due to membrane rupture by the NTP discharge followed by the attack of the reactive species produced in the solution. The E. coli inactivation was only partial using argon as plasma gas and the direct barrier discharge reactors showed partial inactivation even when air was used as plasma gas.

Optimisation of treatment conditions for reducing Shewanella putrefaciens and Salmonella Typhimurium on grass carp treated by thermoultrasound-assisted plasma functionalized buffer

A novel method of thermoultrasound-assisted plasma functionalized buffer (PFB) for decontaminating grass carp was evaluated using the Box-Behnken design (BBD) with processing variables including PFB generating voltage (PV), ultrasound treatment time (UT) and temperature (TP). The predicted models were found to be significant (p < 0.05) and displayed sufficient fitness with experimental data as indicated by non-significant (p > 0.05) lack of fit and high coefficient of determination (R2≥0.97) values. The optimum decontamination conditions for the responses of S. putrefaciens and S. Typhimurium were PV of 66 V, UT of 14.90 min and TP of 60 ℃, achieving reductions of 4.40 and 3.97 log CFU/g, respectively, with a desirability of 0.998. Among the variables, temperature presented higher significance for inactivating bacteria and the production of volatile basic nitrogen and lipid peroxidation under the optimized conditions were within the limits of freshness for grass carp. Additionally, the effects of PFB and the optimized thermoultrasound-assisted PFB decontamination were mild on the microstructure of grass carp with slight ruptures and loose myofibril structures, indicating the potential of thermoultrasound-assisted PFB for seafood products decontamination with reduced processing time.