Membrane damage and active but nonculturable state in liquid cultures of Escherichia coli treated with an atmospheric pressure plasma jet

Formation and resuscitation of viable but non-culturable (VBNC) yeast in the food industry: A review

The viable but non-culturable (VBNC) state is a survival strategy adopted by microorganisms in response to unfavorable conditions in the environment. VBNC cells are unable to form colonies but still maintain a low level of activity, posing a potential threat to food safety and public health. Therefore, the development of effective strategies to prevent the formation and resuscitation of VBNC cells of microorganisms is a key challenge in food science and microbiology research. However, current research on VBNC cells has primarily focused on bacteria, with relatively limited reports on fungi. This paper provides a comprehensive and systematic review of yeast in the VBNC state, discussing various factors that induce and facilitate resuscitation, along with detection methods and formation and recovery mechanisms. A comprehensive understanding of the induction and resuscitation of yeast in the VBNC state and exploration of its molecular mechanism hold significant implications for food safety and public health. It is imperative to enhance our comprehension of the underlying mechanisms and contributory factors pertaining to VBNC yeast, thereby facilitating the efficient management of the food fermentation process and ensuring the integrity of food quality and safety.

Insight into the surface discharge cold plasma efficient inactivation of Pseudomonas fluorescens in water based on exogenous reactive oxygen and nitrogen species: Synergistic mechanism and energy benefits

As well known, surface discharge cold plasma has efficient inactivation ability and a variety of RONS are main active particles for inactivation, but their synergistic mechanism is still not clear. Therefore, surface discharge cold plasma system was applied to treat Pseudomonas fluorescens to study bacterial inactivation mechanism and energy benefit. Results showed that energy efficiency was directly proportional to applied voltage and inversely proportional to initial concentration. Cold plasma treatment for 20 min was inactivated by approximately > 4-log10Pseudomonas fluorescens and application of •OH and 1O2 scavengers significantly improved survival rate. In addition, •OH and 1O2 destroyed cell membrane structure and membrane permeability, which promoted diffusion of RONS into cells and affecting energy metabolism and antioxidant capacity, leading to bacterial inactivation. Furthermore, accumulation of intracellular NO and ONOOH was related to infiltration of exogenous RNS, while accumulation of •OH, H2O2, 1O2, O2- was the result of joint action of endogenous and exogenous ROS. Transcriptome analysis revealed that different RONS of cold plasma were responsible for Pseudomonas fluorescens inactivation and related to activation of intracellular antioxidant defense system and regulation of genes expression related to amino acid metabolism and energy metabolism, which promoting cellular process, catalytic activity and other biochemical pathways.

Plasma-activated water: Candidate hand disinfectant for SARS-CoV-2 transmission disruption

The global epidemic caused by SARS-CoV-2 has brought about worldwide burden and a sense of danger for more than two years, leading to a wide range of social, public health, economic and environmental issues. Self-inoculation through hands has been the primary way for environmental transmission of SARS-CoV-2. Plasma-activated water (PAW) has been reported as an effective, safe and environmentally friendly disinfectant against SARS-CoV-2. However, the inactivating effect of PAW on SARS-CoV-2 located on skin surface and its underlying mechanism of action have not been elucidated. In this study, PAW was prepared using an air-pressure plasma jet device. The antiviral efficiency of PAW1, PAW3, and PAW5 on the SARS-CoV-2 pseudovirus was 8.20 % (±2.88 %), 46.24 % (±1.79 %), and 91.71 % (±0.47 %), respectively. Additionally, determination of PAW's physicochemical properties, identification of major sterile effector in PAW, transmission electron microscopy analysis, malondialdehyde (MDA) assessment, SDS-PAGE, ELISA, and qPCR were conducted to reveal the virucidal mechanism of PAW. Our experimental results suggested that peroxynitrite, which was generated by the synergism of acidic environment and reactive species, was the major sterile effector of PAW. Furthermore, we found that PAW treatment significantly inactivated SARS-CoV-2 pseudovirus through the destruction of its structure of and the degradation of the viral RNA. Therefore, the possible mechanism for the structural destruction of SARS-COV-2 by PAW is through the action of peroxynitrite generated by the synergism of acidic environment and reactive species, which might react with and destroy the lipid envelope of SARS-CoV-2 pseudovirus. Nevertheless, further studies are required to shed light on the interaction mechanism of PAW-inherent RONS and viral components, and to confirm the determinant factors for virus inactivation of SARS-COV-2 by PAW. Therefore, PAW may be a candidate hand disinfectant used to disrupt the transmission of SARS-CoV-2.

Efficient degradation of p-nitrophenol from water by enhancing dielectric barrier discharge (DBD) plasma through ozone circulation: Optimization, kinetics and mechanism

Non-thermal dielectric barrier discharge (DBD) plasma has received great attention for degradation of persistent organic pollutants such as p-nitrophenol (PNP). However, the feasibility of the DBD implementation is not clear due to its high energy consumption and relatively low degradation efficiency. In this research, a novel strategy was suggested based on re-circulation of the generated O3 in the DBD system to enhance the PNP degradation efficiency and energy yield. The potential mechanism and possible pathway of PNP degradation were studied by EPR, ESR, DFT and GS-MS analytical tests. According to the results, the PNP degradation efficiency and energy yield increased from 57.4% to 94.4% and from 0.52 to 1.18 g kW-1h-1, respectively through ozone circulation into the DBD reactor. This was due to the more release of long-lived and short-lived reactive species (ROS) in the DBD-O3 system by the O3 circulation. The variations in pH (4-10), initial concentration (50-90 mg L-1), and the presence of co-existing substances in the water matrix had minimal impact on the DBD-O3 system, in comparison to the conventional system. The biological toxicity evaluation revealed that the hybrid DBD-O3 system transform PNP to less toxic intermediates. This study proposes a promising strategy to improve the utilization of DBD for the degradation of PNP.

Understanding the transition to viable but non-culturable state in Escherichia coli W3110: a comprehensive analysis of potential spectrochemical biomarkers

The viable but non-culturable (VBNC) state is considered a survival strategy employed by bacteria to endure stressful conditions, allowing them to stay alive. Bacteria in this state remain unnoticed in live cell counts as they cannot proliferate in standard culture media. VBNC cells pose a significant health risk because they retain their virulence and can revive when conditions normalize. Hence, it is crucial to develop fast, reliable, and cost-effective methods to detect bacteria in the VBNC state, particularly in the context of public health, food safety, and microbial control assessments. This research examined the biomolecular changes in Escherichia coli W3110 induced into the VBNC state in artificial seawater under three different stress conditions (temperature, metal, and antibiotic). Initially, confirmation of VBNC cells under various stresses was done using fluorescence microscopy and plate counts. Subsequently, lipid peroxidation was assessed through the TBARS assay, revealing a notable increase in peroxidation end-products in VBNC cells compared to controls. ATR-FTIR spectroscopy and chemomometrics were employed to analyze biomolecular changes, uncovering significant spectral differences in RNA, protein, and nucleic acid concentrations in VBNC cells compared to controls. Notably, RNA levels increased, while protein and nucleic acid amounts decreased. ROC analyses identified the 995 cm- 1 RNA band as a consistent marker across all studied stress conditions, suggesting its potential as a robust biomarker for detecting cells induced into the VBNC state under various stressors.

Proteomic profiling of antibiotic-resistant Escherichia coli GW-AmxH19 isolated from hospital wastewater treated with physical plasma

Microorganisms which are resistant to antibiotics are a global threat to the health of humans and animals. Wastewater treatment plants are known hotspots for the dissemination of antibiotic resistances. Therefore, novel methods for the inactivation of pathogens, and in particular antibiotic-resistant microorganisms (ARM), are of increasing interest. An especially promising method could be a water treatment by physical plasma which provides charged particles, electric fields, UV-radiation, and reactive species. The latter are foremost responsible for the antimicrobial properties of plasma. Thus, with plasma it might be possible to reduce the amount of ARM and to establish this technology as additional treatment stage for wastewater remediation. However, the impact of plasma on microorganisms beyond a mere inactivation was analyzed in more detail by a proteomic approach. Therefore, Escherichia coli GW-AmxH19, isolated from hospital wastewater in Germany, was used. The bacterial solution was treated by a plasma discharge ignited between each of four pins and the liquid surface. The growth of E. coli and the pH-value decreased during plasma treatment in comparison with the untreated control. Proteome and antibiotic resistance profile were analyzed. Concentrations of nitrite and nitrate were determined as long-lived indicative products of a transient chemistry associated with reactive nitrogen species (RNS). Conversely, hydrogen peroxide served as indicator for reactive oxygen species (ROS). Proteome analyses revealed an oxidative stress response as a result of plasma-generated RNS and ROS as well as a pH-balancing reaction as key responses to plasma treatment. Both, the generation of reactive species and a decreased pH-value is characteristic for plasma-treated solutions. The plasma-mediated changes of the proteome are discussed also in comparison with the Gram-positive bacterium Bacillus subtilis. Furthermore, no effect of the plasma treatment, on the antibiotic resistance of E. coli, was determined under the chosen conditions. The knowledge about the physiological changes of ARM in response to plasma is of fundamental interest to understand the molecular basis for the inactivation. This will be important for the further development and implementation of plasma in wastewater remediation.

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.

Enhanced Biofilm Formation by Tetracycline in a Staphylococcus aureus Naturally Lacking ica Operon and atl

Staphylococcus aureus is a major, widespread pathogen, and its biofilm-forming characteristics make it even more difficult to eliminate by biocides. Tetracycline (TCY) is a major broad-spectrum antibiotic, the residues of which can cause deleterious health impacts, and subinhibitory concentrations of TCY have the potential to increase biofilm formation in S. aureus. In this study, we showed how the biofilm formation of S. aureus 123786 is enhanced in the presence of TCY at specific subinhibitory concentrations. S. aureus 123786 used in this study was identified as Staphylococcal Cassette Chromosome mec III, sequence type239 and naturally lacking ica operon and atl gene. Two assays were performed to quantify the formation of S. aureus biofilm. In the crystal violet (CV) assay, the absorbance values of biofilm stained with CV at optical density (OD)540 nm increased after 8 and 16 hr of incubation when the concentration of TCY was 1/2 minimum inhibitory concentration (MIC), whereas at the concentration of 1/16 MIC, the absorbance values increased after 16 and 24 hr of incubation. In tetrazolium salt reduction assay, the absorbance value at OD490 nm of S. aureus 123786 biofilms mixed with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium solution increased after 8 hr when the concentration of TCY was 1/4 MIC, which may be correlated with the higher proliferation and maturation of biofilm. In conclusion, the biofilm formation of S. aureus 123786 could be enhanced in the presence of TCY at specific subinhibitory concentrations.

Bactericidal efficacy difference between air and nitrogen cold atmospheric plasma on Bacillus cereus: Inactivation mechanism of Gram-positive bacteria at the cellular and molecular level

As an emerging food processing technology, cold atmospheric plasma (CAP) has attracted great attention in the field of microbial inactivation. Although CAP has been proven to effectively inactivate a variety of foodborne pathogens, there is less research on the inactivation of Bacillus cereus, and the exact inactivation mechanism is still unclear. Elucidating the inactivation mechanism will help to develop and optimize this sterilization method, with the prospective application in industrialized food production. This study aims to explore the bactericidal efficacy difference between air and nitrogen CAP on B. cereus, a typical Gram-positive bacterium, and reveals the inactivation mechanism of CAP at the cellular and molecular level, by observing the change of the cell membrane, cell morphological damage, intracellular antioxidant enzyme activity and cellular biomacromolecules changes. The results showed that both air CAP and nitrogen CAP could effectively inactivate B. cereus, which was due to the reactive oxygen and nitrogen species (RONS) generated by the plasma causing bacterial death. The damage pathways of CAP on Gram-positive bacteria could be explained by disrupting the bacterial cell membrane and cell morphology, disturbing the intracellular redox homeostasis, and destroying biomacromolecules in the cells. The differences in active species generated by the plasma were the main reason for the different bactericidal efficiencies of air CAP and nitrogen CAP, where air CAP producing RONS with stronger oxidative capacity in a shorter time. This study indicates that air CAP is an effective, inexpensive and green technology for B. cereus inactivation, providing a basis for industrial application in food processing.

Viable but nonculturable (VBNC) state, an underestimated and controversial microbial survival strategy

As a unique microbial response to adverse circumstances, the viable but nonculturable (VBNC) state is characterized by the loss of culturability of microbial cells on/in nutrient media that normally support their growth, while maintaining metabolic activity. These cells can resuscitate to a culturable state under suitable conditions. Given the intrinsic importance of the VBNC state and recent debates surrounding it, there is a need to redefine and standardize the term, and to address essential questions such as 'How to differentiate VBNC from other similar terms?' and 'How can VBNC cells be standardly and accurately determined?'. This opinion piece aims at contributing to an improved understanding of the VBNC state and promoting its proper handling as an underestimated and controversial microbial survival strategy.

Study of coaxial-dual-gap dielectric barrier discharge based on capillary: discharge characteristics and Escherichia coli decontamination

AIMS

The medical capillary catheters occupy a high proportion of medical diagnosis, monitoring, and treatment devices, and will cause serious cross-infection without being disinfected adequately. This paper presents a new plasma structure for efficient inactivation of harmful microorganisms in medical capillaries.

METHODS AND RESULTS

An innovative coaxial-dual-gap dielectric barrier discharge reactor powered by nanosecond-pulsed power supply was designed for disinfection of Escherichia coli (E. coli) inside and outside medical capillary catheters in this work. Atmospheric helium plasma (AHP) and atmospheric air plasma (AAP) were successfully obtained inside and outside capillary (0.6 mm inner diameter and 1.0 mm outer diameter), respectively. The electrical and optical characteristics of AHP and AAP were investigated. As the threshold of applied voltage amplitude (Uamp) was <7.0 kV, only one helium glow discharge was generated inside the capillary at the rising and falling stages of pulse voltage. As the Uamp exceeded the threshold, two helium glow discharges were generated that further caused generation of air discharge. Under the Uamp of 9.0 kV, the production of AHP lowered the breakdown voltage in air gap, resulting in the formation of high-volume and uniform AAP, which was conducive to the realization of full inactivation. The inactivation rates of E. coli reached 98.13% and 99.99% by 2 min AHP and 0.5 min AAP treatment, respectively.

CONCLUSIONS

The electrical stress of AHP and the reactive oxygen and nitrogen species produced by AAP were contributed to the inactivation of E. coli. The results of SEM (Scanning Electron Microscope) show that plasma treatment can destroy the cellular structure of E. coli.

Research Progress and Future Trends of Low Temperature Plasma Application in Food Industry: A Review

Food nutrition, function, sensory quality and safety became major concerns to the food industry. As a novel technology application in food industry, low temperature plasma was commonly used in the sterilization of heat sensitive materials and is now widely used. This review provides a detailed study of the latest advancements and applications of plasma technology in the food industry, especially the sterilization field; influencing factors and the latest research progress in recent years are outlined and upgraded. It explores the parameters that influence its efficiency and effectiveness in the sterilization process. Further research trends include optimizing plasma parameters for different food types, investigating the effects on nutritional quality and sensory attributes, understanding microbial inactivation mechanisms, and developing efficient and scalable plasma-based sterilization systems. Additionally, there is growing interest in assessing the overall quality and safety of processed foods and evaluating the environmental sustainability of plasma technology. The present paper highlights recent developments and provides new perspectives for the application of low temperature plasma in various areas, especially sterilization field of the food industry. Low temperature plasma holds great promise for the food industry's sterilization needs. Further research and technological advancements are required to fully harness its potential and ensure safe implementation across various food sectors.

Conjugation transfer of plasma-induced sublethal antibiotic resistance genes under photoreactivation: Alleviation mechanism of intercellular contact

Dissemination of antibiotic resistance genes (ARGs) is a huge challenge worldwide. Information regarding underlying mechanisms of conjugation transfer of sublethal ARGs under photoreactivation is still lacking. In this study, experimental exploration and model prediction were conducted to evaluate the effects of photoreactivation on conjugation transfer of plasma-induced sublethal ARGs. The experimental results showed that reactive species (O₂^-•, ¹O₂, and •OH) generated in the plasma process led to 0.32, 1.45, 3.21, 4.10, and 3.96-log removal for tetC, tetW, bla_TEM-1, aac(3)-II, and intI1 after 8 min treatment at 18 kV, respectively. Their attacks led to breakage and mineralization of ARGs-containing DNA and disturbance of bacterial metabolism. The conjugation transfer frequency increased by 0.58-fold after 48 h of photoreactivation compared with the plasma treatment, as well as the abundances of ARGs and reactive oxygen species levels. The alleviation effects of photoreactivation were independent of cell membrane permeability, but related to promotion of intercellular contact. Ordinary differential equation model predicted that the stabilization time of long-term transfer of ARGs significantly increased by 50 % after photoreactivation compared with the plasma treatment, and the conjugation transfer frequency also increased. This study firstly revealed the mechanisms of conjugation transfer of sublethal ARGs under photoreactivation.

Advances of non-thermal plasma discharge technology in degrading recalcitrant wastewater pollutants. A comprehensive review

With development and urbanization, the amount of wastewater generated due to human activities drastically increases yearly, causing water pollution and intensifying the already worsened water crisis. Although convenient, conventional wastewater treatment methods such as activated sludge, stabilization ponds, and adsorption techniques cannot fully eradicate the complex and recalcitrant contaminants leading to toxic byproducts generation. Recent advancements in wastewater treatment techniques, specifically non-thermal plasma technology, have been extensively investigated for the degradation of complex pollutants in wastewater. Non-thermal plasma is an effective alternative for degrading and augmenting the biodegradability of recalcitrant pollutants due to its ability to generate reactive species in situ. This article critically reviews the non-thermal plasma technology, considering the plasma discharge configuration and reactor types. Furthermore, the influence of operational parameters on the efficiency of the plasma systems and the reactive species generated by the system during discharge has gained significant interest and hence been discussed. Also, the application of non-thermal plasma technology for the degradation of pharmaceuticals, pesticides, and dyes and the inactivation of microbial activities are outlined in this review article. Additionally, optimistic applications involving the combination of non-thermal plasma and catalysts and pilot and industrial-scale projects utilizing non-thermal plasma technology have been addressed. Concluding perceptions on the challenges and future perspectives of the non-thermal technology on wastewater treatment are accentuated. Overall, this review outlines a comprehensive understanding of the non-thermal plasma technology for recalcitrant pollutant degradation from a scientific perspective providing detailed instances for reference.

Current Perspectives on Viable but Non-Culturable Foodborne Pathogenic Bacteria: A Review

Foodborne diseases caused by foodborne pathogens pose risks to food safety. Effective detection and efficient inactivation of pathogenic bacteria has always been a research hotspot in the field of food safety. Complicating these goals, bacteria can be induced to adopt a viable but non-culturable (VBNC) state under adverse external environmental stresses. When in the VBNC state, pathogens cannot form visible colonies during traditional culture but remain metabolically active and toxic. The resulting false negative results in growth-related assays can jeopardize food safety. This review summarizes the latest research on VBNC foodborne pathogens, including induction conditions, detection methods, mechanism of VBNC formation, and possible control strategies. It is hoped that this review can provide ideas and methods for future research on VBNC foodborne pathogenic bacteria.

The Effect of Plasma on Bacteria and Normal Cells in Infected Wound

Infected wound is one of the most common and serious problem in wound management. Cold atmospheric plasma (CAP) is considered to have a good effect in wound healing as a new type medicine. However, there is a key issue that has not been addressed in the treatment of infected wounds by plasma. Bacteria are always found in the deep region of the wound. When plasma is used to treat wounds, it also acts on normal tissue cells while decontaminating. What is the difference between the same dose of plasma acting on bacteria and normal cells? In this study, the most common bacteria (S. aureus, P. aeruginosa, and E. coli) in infected wound and two kinds of normal skin cells (human keratinocyte and human skin fibroblasts (HSF)) were selected to study the difference of the effects of the same dose of plasma on bacteria and cells. The results reveal that three kinds of 10⁶ CFU mL bacteria could be effectively inactivated by 5 order after plasma treatment 3 min, and P. aeruginosa was more sensitive to plasma (could be inactivated 5 order after 2 min treatment). The 10⁴ mL keratinocyte and HSF were treated with the same dose of plasma; keratinocyte can maintain over 90% of the activity and HSF cells can maintain over 70% of the activity. Moreover, the level of collagen I secreted by HSF increased. Therefore, cells can remain a high activity when a plasma dose capable of inactivating bacteria is applied to them.

Treatment of Escherichia coli contaminated water with different pulse-powered NTP configurations and analysis for post treatment efficacy

A cost-effective and energy efficient method for water sterilization is a challenging demand in the present scenario where scarcity of pure water is rising. Non-Thermal Plasma (NTP) finds promising applications in environmental processes and has advantages over conventional water treatment methods. Escherichia coli contaminated water treatment using multiple pin plasma reactor and atmospheric pressure plasma jet reactor was undertaken in this work. High voltage pulsed power was used for generating non-thermal plasma in these reactors and various configurations were tested for treating the contaminated water. The most feasible configuration among these was identified from the treatment efficiency and survival rate plots of E. coli colonies. It was observed that with an exposure of 15 min NTP, 100 percent bacterial removal was achieved using plasma jet reactor configuration. The presence of bacteria after NTP-treated time was also checked and confirmed for complete removal of bacteria. An optimum time of 15 min plasma exposure for 100 ml was found to be effective for complete removal of microorganisms and the sterility was maintained up to 60 min after the treatment. Non-thermal plasma-based treatment of bacteria-contaminated water is found to be promising and could be considered for scale-up and analysis.

Shower water contributes viable nontuberculous mycobacteria to indoor air

Nontuberculous mycobacteria (NTM) are frequently present in municipal drinking water and building plumbing, and some are believed to cause respiratory tract infections through inhalation of NTM-containing aerosols generated during showering. However, the present understanding of NTM transfer from water to air is insufficient to develop NTM risk mitigation strategies. This study aimed to characterize the contribution of shower water to the abundance of viable NTM in indoor air. Shower water and indoor air samples were collected, and 16S rRNA and rpoB genes were sequenced. The sequencing results showed that running the shower impacted the bacterial community structure and NTM species composition in indoor air by transferring certain bacteria from water to air. A mass balance model combined with NTM quantification results revealed that on average 1/132 and 1/254 of NTM cells in water were transferred to air during 1 hour of showering using a rain and massage showerhead, respectively. A large fraction of the bacteria transferred from water to air were membrane-damaged, i.e. they had compromised membranes based on analysis by live/dead staining and flow cytometry. However, the damaged NTM in air were recoverable as shown by growth in a culture medium mimicking the respiratory secretions of people with cystic fibrosis, implying a potential infection risk by NTM introduced to indoor air during shower running. Among the recovered NTM, Mycobacterium mucogenicum was the dominant species as determined by rpoB gene sequencing. Overall, this study lays the groundwork for future pathogen risk management and public health protection in the built environment.

Limited Role of Rhamnolipids on Cadmium Resistance for an Endogenous-Secretion Bacterium

Rhamnolipids, a type of biosurfactant, represent a potential strategy for both enhancing organismic resistance and in situ remediation of heavy metals contaminations. In-depth study of the mechanism of rhamnolipids synthesis in response to heavy metals stress, is indispensable for a wide use of biosurfactant-secreting microbes in bioremediation. In this study, we employed the wild-type and the rhlAB deficient strain (ΔrhlAB) of Pseudomonas aeruginosa, a prototypal rhamnolipids-producing soil microorganism, to investigate its responses to cadmium resistance based on its physicochemical, and physiological properties. Compared with the wild-type strain, the ΔrhlAB were more sensitive to Cd-stress at low Cd concentration (<50 mg/L), whereas there was little difference in sensitivity at higher Cd concentrations, as shown by spot titers and cell viability assays. Secreted rhamnolipids reduced intracellular Cd²⁺ accumulation to alleviate Cd²⁺ stress, whereas endogenous rhamnolipids played a limited role in alleviating Cd²⁺ stress. Synthesized rhamnolipids exhibited a higher critical micelle concentration (CMC) (674.1 mg/L) and lower emulsification index (4.7%) under high Cd-stress, while these parameters showed no obvious changes. High Cd-stress resulted in high hydrophilic wild-type bacterial surface and lower bioremediation ability. This study could advance a deeper understanding of the mechanism of cadmium resistance and provide a theoretical foundation for the application of biosurfactant and biosurfactant-secreted bacterium in contaminant bioremediation.

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.

Study of the synergistic effect of singlet oxygen with other plasma-generated ROS in fungi inactivation during water disinfection

Cold atmospheric plasma (CAP) possesses the ability of high-efficiency disinfection. It is reported that mixtures of reactive oxygen species (ROS) including ^·OH, ¹O₂, O₂^- and H₂O₂ generated from CAP have better antimicrobial ability than mimicked solution of mixture of single ROS type, but the reason is not clear. In this study, CAP was applied to treat yeasts in water in order to investigate the fungal inactivation efficiency and mechanism. The results showed that plasma treatment for 5 min could result in >2-log reduction of yeast cells, and application of varied ROS scavengers could significantly increase the yeast survival rate, indicating that ^·OH and ¹O₂ played the pivotal role in yeast inactivation. Moreover, the synergistic effect of ¹O₂ with other plasma-generated ROS was revealed. ¹O₂ could diffuse into cells and induce the depolarization of mitochondrial membrane potential (MMP), and different levels of MMP depolarization determined different cell death modes. Mild damage of mitochondria during short-term plasma treatment could lead to apoptosis. For long-term plasma treatment, the cell membrane could be severely damaged by the plasma-generated ^·OH, so a large amount of ¹O₂ could induce more depolarization of MMP, leading to increase of intracellular O₂^- and Fe²⁺ which subsequently caused cell inactivation. ¹O₂ could also induce protein aggregation and increase of RIP1/RIP3 necrosome, leading to necroptosis. With participation of ¹O₂, endogenous ^·OH could also be generated via Fenton and Haber-Weiss reactions during plasma treatment, which potentiated necroptosis. Adding l-His could mitigate membrane damage, inhibit the drop of MMP and the formation of necrosome, and thus prevent the happening of necroptosis. These findings may deepen the understanding of plasma sterilization mechanisms and provide guidance for microbial killing in the environment.

A Lesion Microenvironment-Responsive Fungicide Nanoplatform for Crop Disease Prevention and Control

Controlled fungicide delivery in response to the specific microenvironment produced by fungal pathogens is an advisable strategy to improve the efficacy of fungicides. Herein, the authors construct a smart fungicide nanoplatform, using mesoporous silica nanoparticles (MSNs) as nanocarriers loaded with eugenol (EU) and Ag⁺ coordinated polydopamine (Ag⁺ -PDA) as a coating to form Ag⁺ -PDA@MSNs-EU NPs for Botrytis cinerea (B. cinerea) control. As a botanical fungicide, EU offers an eco-friendly alternative to synthetic fungicides and can upregulate several defense-related genes in the tomato plant. The Ag⁺ -PDA coating can lock the EU inside the nanocarriers and respond to the oxalic acid produced by B. cinerea to corelease the loaded EU and Ag⁺ . The results demonstrate that Ag⁺ -PDA@MSNs-EU NPs can effectively inhibit the mycelial growth of B. cinerea on detached and potted tomato leaves. The construction of such a smart fungicide nanoplatform provides new guidance to design controlled fungicides release systems, which can respond to the microenvironment associated with plant pathogen to realize fungus control.

Combined use of ultrasound-assisted washing with in-package atmospheric cold plasma processing as a novel non-thermal hurdle technology for ready-to-eat blueberry disinfection

Ultrasound (US) has limited disinfection efficacy, and it has been recommended to combine it with chemical disinfectants during fresh produce washing. After washing and before packaging, the disinfection effect of US-assisted washing can be weakened; thus, in-package disinfection is important. As a nutritious fruit, there are no packaged blueberries can be directly eaten. Therefore, in this study, blueberry was selected as the model, and the two most commonly used disinfectants (free chlorine [FC] at 10 ppm and peracetic acid [PAA] at 80 ppm) were combined with low-frequency US (25 kHz) during washing, followed by in-package disinfection using dielectric barrier discharge cold plasma (CP). The disinfection efficacy of US-FC and US-PAA against Escherichia coli O157:H7 and Salmonella Typhimurium was significantly higher than that of US, PAA, or FC alone. The highest disinfection efficacy of CP was observed at the pulse frequency range of 400-800 Hz. For US-FC (1 min) + CP (1 min), an additional 0.86, 0.71, 0.42, and 0.29 log CFU/g of reduction for E. coli O157:H7, S. Typhimurium, aerobic mesophilic counts, and mold and yeast was achieved, respectively, compared with US-FC (2 min) alone. For US-PAA (1 min) + CP (1 min) an additional 0.71, 0.59, 0.32, and 0.21 log CFU/g of reduction was achieved for the above organisms, respectively, compared with US-PAA (2 min) alone. Quality loss (in total color difference, firmness, and anthocyanin content) was not observed after treatment with US-FC + CP, US-PAA + CP, US-FC, or US-PAA. After treatment with US-FC + CP or US-PAA + CP, the reactive oxygen species (ROS) content was significantly lower than that in the other groups, and antioxidant enzyme activity was significantly higher than that in the other groups, suggesting that in-package CP can activate the blueberry antioxidant system to scavenge ROS, thereby lowering the risk of quality loss. US-CP combination not only improves the disinfection efficacy but also lowers quality loss caused by ROS, without prolonging the processing time.

Environmental free radicals efficiently inhibit the conjugative transfer of antibiotic resistance by altering cellular metabolism and plasmid transfer

Spread of antibiotic-resistant genes (ARGs) is a global public safety issue and inhibition their transfer is imperative. In this study, a novel strategy using environmental free radical exposure was developed to inhibit conjugative transfer of ARGs (RP4 plasmid) in aqueous solutions. Long-time free radical (·OH, 1O2, and O2·-) exposure significantly suppressed the conjugative transfer frequency of ARGs between Escherichia coli (E. coli) strains, and ·OH was more likely to attack ARG, thereby inhibiting the conjugate transfer frequency, compared to 1O2 and O2·-. Compared with the control, the conjugative transfer frequency significantly decreased from 4.08 × 10-5 to 1.2 × 10-8 after 10 min free radical exposure, confirming that the transfer and proliferation of ARGs were well inhibited. Correspondingly, the number of transconjugant significantly decreased by 61.7% after 10 min free radical exposure. Significant reductions in reactive oxygen species levels (ROS content and enzyme levels) and DNA damage-induced responses in the donor strains were observed after 10 min free radical exposure. Concurrently, intercellular contact was also weakened via inhibiting the synthesis of polysaccharides in extracellular polymeric substances. Moreover, the expressions of plasmid transfer genes were down-regulated after 10 min exposure due to the shortage of adenosine-triphosphate supply. This study firstly disclosed the underneath mechanisms for depressing ARGs transfer and dissemination via environmental free radical exposure.

Evaluation of the Effects of Cold Plasma on Cell Membrane Lipids and Oxidative Injury of Salmonella typhimurium

Salmonella typhimurium (S. typhimurium) is a major causative agent of foodborne illness worldwide. Cold plasma (CP) was used to inactivate S. typhimurium and to investigate the effect of CP on cell membrane lipids and oxidative injury of cells. Results indicated that the inactivation effect of CP on S. typhimurium was positively correlated with the treatment time and voltage. S. typhimurium was undetectable (total number of surviving colonies <2 log CFU/mL) after 5 min treatment with the voltage of 50 V. CP treatment caused damage to the cell membrane of S. typhimurium and the leakage of cell contents, and the relative content of unsaturated fatty acids in cell membrane decreased. Cell membrane lipids were oxidized; the malondialdehyde content increased from 0.219 nmol/mL to 0.658 nmol/mL; the catalase activity of S. typhimurium solution increased from 751 U/mL to 2542 U/mL; and the total superoxide dismutase activity increased from 3.076 U/mL to 4.54 U/mL, which confirmed the oxidative damage in S. typhimurium cell membrane caused by CP treatment. It was demonstrated that the potential application of plasma-mediated reactive oxygen species is suitable for destroying the structures of the cell membrane and ensuring the microbial safety of fresh food samples.

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.

Applications of Plasma-Activated Liquid in the Medical Field

Much progress has been made since plasma was discovered in the early 1900s. The first form of plasma was thermal type, which was limited for medical use due to potential thermal damage on living cells. In the late 1900s, with the development of a nonthermal atmospheric plasma called cold plasma, profound clinical research began and ‘plasma medicine’ became a new area in the academic field. Plasma began to be used mainly for environmental problems, such as water purification and wastewater treatment, and subsequent research on plasma and liquid interaction led to the birth of ‘plasma-activated liquid’ (PAL). PAL is currently used in the fields of environment, food, agriculture, nanoparticle synthesis, analytical chemistry, and sterilization. In the medical field, PAL usage can be expanded for accessing places where direct application of plasma is difficult. In this review, recent studies with PAL will be introduced to inform researchers of the application plan and possibility of PAL in the medical field.

Plasma induced efficient removal of antibiotic-resistant Escherichia coli and antibiotic resistance genes, and inhibition of gene transfer by conjugation

Antibiotic-resistant bacteria (ARB) and their resistance genes (ARGs) are emerging environmental pollutants that pose great threats to human health. In this study, a novel strategy using plasma was developed to simultaneously remove antibiotic-resistant Escherichia coli (AR bio-56954 E. coli) and its ARGs, aiming to inhibit gene transfer by conjugation. Approximately 6.6 log AR bio-56954 E. coli was inactivated within 10 min plasma treatment, and the antibiotic resistance to tested antibiotics (tetracycline, gentamicin, and amoxicillin) significantly decreased. Reactive oxygen and nitrogen species (RONS) including •OH, ¹O₂, O₂•^-, NO₂^-, and NO₃^- contributed to ARB and ARGs elimination; their attacks led to destruction of cell membrane, accumulation of excessive intracellular reactive oxygen substances, deterioration of conformational structures of proteins, and destroy of nucleotide bases of DNA. As a result, the ARGs (tet(C), tet(W), blaTEM-1, aac(3)-II), and integron gene intI1), and conjugative transfer frequency of ARGs significantly decreased after plasma treatment. The results demonstrated that plasma has great prospective application in removing ARB and ARGs in water, inhibiting gene transfer by conjugation.

Inhibited conjugative transfer of antibiotic resistance genes in antibiotic resistant bacteria by surface plasma

Antibiotic resistant bacteria (ARB) and resistance genes (ARGs) are emerging environmental pollutants with strong pathogenicity. In this study, surface plasma was developed to inactivate the donor ARB with Escherichia coli (AR E. coli) as a model, eliminate ARGs, and inhibit conjugative transfer of ARGs in water, highlighting the influences of concomitant inorganic ions. Surface plasma oxidation significantly inactivated AR E. coli, eliminated ARGs, and inhibited conjugative transfer of ARGs, and the presence of NO₃^-, Cu²⁺, and Fe²⁺ all promoted these processes, and SO₄^2- did not have distinct effect. Approximately 4.5log AR E. coli was inactivated within 10 min treatment, and it increased to 7.4log AR E. coli after adding Fe²⁺. Integrons intI1 decreased by 3.10log (without Fe²⁺) and 4.43log (adding Fe²⁺); the addition of Fe²⁺ in the surface plasma induced 99.8% decline in the conjugative transfer frequency. The inhibition effects on the conjugative transfer of ARGs were mainly attributed to the reduced reactive oxygen species levels, decreased DNA damage-induced response, decreased intercellular contact, and down-regulated expression of plasmid transfer genes. This study disclosed underlying mechanisms for inhibiting ARGs transfer, and supplied a prospective technique for ARGs control.

Impact of electrical grounding conditions on plasma-liquid interactions using Thomson scattering on a pulsed argon jet

The interaction between an argon plasma jet excited using microsecond duration voltage pulses and a liquid target was examined using Thomson scattering to quantify the temporal evolution of the electron density and temperature. The electrical resistance between a liquid target and the electrical ground was varied from 1 to [Formula: see text] to mimic different conductivity liquids while the influence of the varying electrical properties on the electron dynamics within the plasma were examined. It was demonstrated that the interaction between the plasma jet and a liquid target grounded via a high resistance resulted in typical dielectric barrier discharge behaviour, with two discharge events per applied voltage pulse. Under such conditions, the electron density and temperature reached a peak of [Formula: see text] and 3.4 eV, respectively; with both rapidly decaying over several hundreds of nanoseconds. For liquid targets grounded via a low resistance, the jet behaviour transitioned to a DC-like discharge, with a single breakdown event being observed and sustained throughout the duration of each applied voltage pulse. Under such conditions, electron densities of [Formula: see text] were detected for several microseconds. The results demonstrate that the electron dynamics in a pulsed argon plasma jet are extremely sensitive to the electrical characteristics of the target, which in the case of water, can evolve during exposure to the plasma.

Excess sludge disintegration by discharge plasma oxidation: Efficiency and underlying mechanisms

A huge amount of excess sludge is inevitably produced in wastewater treatment, and it is becoming more and more urgent to realize efficient sludge reduction. Discharge plasma oxidation was used to efficiently disintegrate excess sludge for sludge reduction in this study. Approximately 18.22% sludge disintegration and 27.8% reduction of total suspended solids (TSS) were achieved by discharge plasma treatment. The water content of the filter cake decreased from 81.9% to 76.0% and the bound water content decreased from 2.66 g/g dry solid to 0.73 g/g dry solid after treatment. The large quantities of reactive oxygen species (ROS) generated by discharge plasma played important roles in sludge disintegration by destroying flocs and promoting the transformation of organic substances. Concurrent cell lysis induced by ROS oxidation released intracellular organics and water into the liquid phase. The fraction of soluble extracellular polymer substances (S-EPS) was enhanced from 16.10% to 58.51%, whereas the tightly bound fraction was reduced from 70.62% to 28.91%. Migration and decomposition of EPS were the main processes for EPS changing at a low oxidation capacity, whereas cell lysis became important at a high oxidation capacity. In summary, the plasma treatment effectively improved sludge disintegration.

Delivery and expression of plasmid DNA into cells by a novel non-thermal plasma source

Medical applications such as plasma assisted gene transfer is a minimally invasive approach that can substantially reduce potential discomfort of treated area. Atmospheric pressure plasma discharge is an effective approach to deliver plasmid DNA for in vitro and in vivo applications. We investigated plasma assisted delivery in vitro in mouse melanoma cells (B16F10) using a novel surface plasma device, which is operated in air. We evaluated the influence of applied voltage and distance between the surface device and cell monolayer. We found no significant effect on the viability of cells. Highest expression following delivery of a plasmid encoding green fluorescent protein was achieved with an applied voltage of 11.25 kV at a 2 mm distance and 5 s exposure time. To better understand the influence of oxidative damages and stress on cells after plasma delivery, a mRNA expression study was performed. Our results indicated that TNFα mRNA was significantly upregulated. The mRNA response may be attributed to the RONS generated by plasma; however, this mRNA upregulation was not adequate to be reflected in a coordinate protein upregulation. From the results reported here, it is clear that this novel plasma device could be used for plasmid delivery.

Guidelines on reporting treatment conditions for emerging technologies in food processing

In the last decades, different non-thermal and thermal technologies have been developed for food processing. However, in many cases, it is not clear which experimental parameters must be reported to guarantee the experiments' reproducibility and provide the food industry a straightforward way to scale-up these technologies. Since reproducibility is one of the most important science features, the current work aims to improve the reproducibility of studies on emerging technologies for food processing by providing guidelines on reporting treatment conditions of thermal and non-thermal technologies. Infrared heating, microwave heating, ohmic heating and radiofrequency heating are addressed as advanced thermal technologies and isostatic high pressure, ultra-high-pressure homogenization sterilization, high-pressure homogenization, microfluidization, irradiation, plasma technologies, power ultrasound, pressure change technology, pulsed electric fields, pulsed light and supercritical CO₂ are approached as non-thermal technologies. Finally, growing points and perspectives are highlighted.

Effects of Non-Thermal Plasma on Yeast Saccharomyces cerevisiae

Cold plasmas generated by various electrical discharges can affect cell physiology or induce cell damage that may often result in the loss of viability. Many cold plasma-based technologies have emerged in recent years that are aimed at manipulating the cells within various environments or tissues. These include inactivation of microorganisms for the purpose of sterilization, food processing, induction of seeds germination, but also the treatment of cells in the therapy. Mechanisms that underlie the plasma-cell interactions are, however, still poorly understood. Dissection of cellular pathways or structures affected by plasma using simple eukaryotic models is therefore desirable. Yeast Saccharomyces cerevisiae is a traditional model organism with unprecedented impact on our knowledge of processes in eukaryotic cells. As such, it had been also employed in studies of plasma-cell interactions. This review focuses on the effects of cold plasma on yeast cells.

Detection and Potential Virulence of Viable but Non-Culturable (VBNC) Listeria monocytogenes: A Review

The detection, enumeration, and virulence potential of viable but non-culturable (VBNC) pathogens continues to be a topic of discussion. While there is a lack of definitive evidence that VBNC Listeria monocytogenes (Lm) pose a public health risk, recent studies suggest that Lm in its VBNC state remains virulent. VBNC bacteria cannot be enumerated by traditional plating methods, so the results from routine Lm testing may not demonstrate a sample's true hazard to public health. We suggest that supplementing routine Lm testing methods with methods designed to enumerate VBNC cells may more accurately represent the true level of risk. This review summarizes five methods for enumerating VNBC Lm: Live/Dead BacLight^TM staining, ethidium monoazide and propidium monoazide-stained real-time polymerase chain reaction (EMA- and PMA-PCR), direct viable count (DVC), 5-cyano-2,3-ditolyl tetrazolium chloride-4',6-diamidino-2-phenylindole (CTC-DAPI) double staining, and carboxy-fluorescein diacetate (CDFA) staining. Of these five supplementary methods, the Live/Dead BacLight^TM staining and CFDA-DVC staining currently appear to be the most accurate for VBNC Lm enumeration. In addition, the impact of the VBNC state on the virulence of Lm is reviewed. Widespread use of these supplemental methods would provide supporting data to identify the conditions under which Lm can revert from its VBNC state into an actively multiplying state and help identify the environmental triggers that can cause Lm to become virulent. Highlights: Rationale for testing for all viable Listeria (Lm) is presented. Routine environmental sampling and plating methods may miss viable Lm cells. An overview and comparison of available VBNC testing methods is given. There is a need for resuscitation techniques to recover Lm from VBNC. A review of testing results for post VBNC virulence is compared.

Subcellular mechanism of microbial inactivation during water disinfection by cold atmospheric-pressure plasma

Although the identification of effective reactive oxygen species (ROS) generated by plasma has been extensively studied, yet the subcellular mechanism of microbial inactivation has never been clearly elucidated in plasma disinfection processes. In this study, subcellular mechanism of yeast cell inactivation during plasma-liquid interaction was revealed in terms of comprehensive factors including cell morphology, membrane permeability, lipid peroxidation, membrane potential, intracellular redox homeostasis (intracellular ROS and H₂O₂, and antioxidant system (SOD, CAT and GSH)), intracellular ionic equilibrium (intracellular H⁺ and K⁺) and energy metabolism (mitochondrial membrane potential, intracellular Ca²⁺ and ATP level). The ROS analysis show that ·OH, ¹O₂, ·O₂^-and H₂O₂ were generated in this plasma-liquid interaction system and ·O₂^-served as the precursor of ¹O₂. Additionally, the solution pH was reduced. Plasma can effectively inactivate yeast cells mainly via apoptosis by damaging cell membrane, intracellular redox and ion homeostasis and energy metabolism as well as causing DNA fragmentation. ROS scavengers (l-His, d-Man and SOD) and pH buffer (phosphate buffer solution, PBS) were employed to investigate the role of five antimicrobial factors (·OH, ¹O₂, ·O₂^-, H₂O₂ and low pH) in plasma sterilization. Results show that they have different influences on the aforementioned cell physiological activities. The ·OH and ¹O₂ contributed most to the yeast inactivation. The ·OH mainly attacked cell membrane and increased cell membrane permeability. The disturb of cell energy metabolism was mainly attributed to ¹O₂. The damage of cell membrane as well as extracellular low pH could break the intracellular ionic equilibrium and further reduce cell membrane potential. The remarkable increase of intracellular H₂O₂ was mainly due to the influx of extracellular H₂O₂ via destroyed cell membrane, which played a little role in yeast inactivation during 10-min plasma treatment. These findings provide comprehensive insights into the antimicrobial mechanism of plasma, which can promote the development of plasma as an alternative water disinfection strategy.

Nonthermal plasma-activated water: A comprehensive review of this new tool for enhanced food safety and quality

Nonthermal plasma (NTP) is an advanced technology that has gained extensive attention because of its capacity for decontaminating food from both biological and chemical sources. Plasma-activated water (PAW), a product of NTP's reaction with water containing a rich diversity of highly reactive oxygen species (ROS) and reactive nitrogen species (RNS), is now being considered as the primary reactive chemical component in food decontamination. Despite exciting developments in this field recently, at present there is no comprehensive review specifically focusing on the comprehensive effects of PAW on food safety and quality. Although PAW applications in biological decontamination have been extensively evaluated, a complete analysis of the most recent developments in PAW technology (e.g., PAW combined with other treatments, and PAW applications in chemical degradation and as curing agents) is nevertheless lacking. Therefore, this review focuses on PAW applications for enhanced food safety (both biological and chemical safeties) according to the latest studies. Further, the subsequent effects on food quality (chemical, physical, and sensory properties) are discussed in detail. In addition, several recent trends of PAW developments, such as curing agents, thawing media, preservation of aquatic products, and the synergistic effects of PAW in combination with other traditional treatments, are also presented. Finally, this review outlines several limitations presented by PAW treatment, suggesting several future research directions and challenges that may hinder the translation of these technologies into real-life applications.

Morphological and physiological changes in Lentilactobacillus hilgardii cells after cold plasma treatment

Atmospheric cold plasma (ACP) inactivation of Lentilactobacillus hilgardii was investigated. Bacteria were exposed to ACP dielectric barrier discharge with helium and oxygen as working gases for 5, 10, and 15 min. The innovative approach in our work for evaluation of bacterial survival was the use in addition to the classical plate culture method also flow cytometry which allowed the cells to be sorted and revealed different physiological states after the plasma treatment. Results showed total inhibition of bacterial growth after 10-min of ACP exposure. However, the analysis of flow cytometry demonstrated the presence of 14.4% of active cells 77.5% of cells in the mid-active state and 8.1% of dead cells after 10 min. In addition, some of the cells in the mid-active state showed the ability to grow again on culture medium, thus confirming the hypothesis of induction of VBNC state in L .hilgardii cells by cold plasma. In turn, atomic force microscopy (AFM) which was used to study morphological changes in L. hilgardii after plasma treatment at particular physiological states (active, mid-active, dead), showed that the surface roughness of the mid-active cell (2.70 ± 0.75 nm) was similar to that of the control sample (2.04 ± 0.55 nm). The lack of considerable changes on the cell surface additionally explains the effective cell resuscitation. To the best of our knowledge, AFM was used for the first time in this work to analyze cells which have been sorted into subpopulations after cold plasma treatment and this is the first work indicating the induction of VBNC state in L. hilgardii cells after exposure to cold plasma.

Plasma-activated water: Physicochemical properties, microbial inactivation mechanisms, factors influencing antimicrobial effectiveness, and applications in the food industry

Novel nonthermal inactivation technologies have been increasingly popular over the traditional thermal food processing methods due to their capacity in maintaining microbial safety and other quality parameters. Plasma-activated water (PAW) is a cutting-edge technology developed around a decade ago, and it has attracted considerable attention as a potential washing disinfectant. This review aims to offer an overview of the fundamentals and potential applications of PAW in the agri-food sector. A detailed description of the interactions between plasma and water can help to have a better understanding of PAW, hence the physicochemical properties of PAW are discussed. Further, this review elucidates the complex inactivation mechanisms of PAW, including oxidative stress and physical effect. In particular, the influencing factors on inactivation efficacy of PAW, including processing factors, characteristics of microorganisms, and background environment of water are extensively described. Finally, the potential applications of PAW in the food industry, such as surface decontamination for various food products, including fruits and vegetables, meat and seafood, and also the treatment on quality parameters are presented. Apart from decontamination, the applications of PAW for seed germination and plant growth, as well as meat curing are also summarized. In the end, the challenges and limitations of PAW for scale-up implementation, and future research efforts are also discussed. This review demonstrates that PAW has the potential to be successfully used in the food industry.

Iturin A Extracted From Bacillus subtilis WL-2 Affects Phytophthora infestans via Cell Structure Disruption, Oxidative Stress, and Energy Supply Dysfunction

Potato late blight, caused by Phytophthora infestans (Mont.) de Bary, represents a great food security threat worldwide and is difficult to control. Recently, Bacillus spp. have been considered biocontrol agents to control many plant diseases. Here, Bacillus subtilis WL-2 was selected as a potent strain against P. infestans mycelium growth, and its functional metabolite was identified as Iturin A via electrospray ionization mass spectrometry (ESI-MS). Analyses using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Iturin A caused cell membrane disruption and an irregular internal cell structure. In addition, Iturin A triggered oxidative stress reactions similarly to reactive oxygen species (ROS) in P. infestans cells and caused mitochondrial damage, including mitochondrial membrane potential (MMP), mitochondrial respiratory chain complex activity (MRCCA), and ATP production decline. These results highlight that the cell structure disruption, oxidative stress, and energy supply dysfunction induced by Iturin A play an important role in inhibiting P. infestans. Additionally, B. subtilis WL-2 and Iturin A have great potential for inhibiting P. infestans mycelium growth and controlling potato late blight in the future.