Potential applications of nonthermal plasmas against biofilm-associated micro-organisms in vitro

Non-invasive physical plasma for preventing radiation dermatitis in breast cancer: Results from an intrapatient-randomised double-blind placebo-controlled trial

Background and Purpose

To investigate the effect of topical non-invasive physical plasma (NIPP), a volatile mix generated out of ambient air, on prevention of acute radiation dermatitis (RD) during and after whole-breast irradiation (WBI).

Materials and Methods

Lateral and medial breast halves were randomised within each patient to receive either 120 s of NIPP or sham treatment daily during WBI. Standard skin care with urea lotion was applied to the whole breast. Blinded acute skin toxicity was assessed weekly for each breast half separately and included clinician- (CTCAE) and patient-reported (modified RISRAS), and objective (spectrophotometry) assessments. As an additional external control, a comparable standard of care (SoC) patient collective from a previous prospective trial was used.

Results

Sixty-four patients were included. There were no significant differences between breast halves. Post-hoc comparison with a similar SoC control collective revealed OR = 0.28 (95% CI 0.11-0.76; p = 0.014) for grade ≥ 2 RD upon WBI completion, along with less hyperpigmentation (p < 0.001), oedema (p = 0.020), dry (p < 0.001) and moist desquamation (p = 0.017), pain, itching, and burning (p < 0.001 for each). Tolerability of NIPP was excellent and side effects were not observed.

Conclusion

Even though there were no differences between intrapatient-randomised breast halves, the overall incidence and severity of acute radiation-induced skin toxicity were considerably lower when compared to a prospectively collected SoC cohort. Our data suggest the potential benefit of NIPP in RD prevention. A randomised trial with a physical control group is warranted to confirm these promising results (DRKS00026225).

Plasma activated water as a pre-treatment strategy in the context of biofilm-infected chronic wounds

Healing and treatment of chronic wounds are often complicated due to biofilm formation by pathogens. Here, the efficacy of plasma activated water (PAW) as a pre-treatment strategy has been investigated prior to the application of topical antiseptics polyhexamethylene biguanide, povidone iodine, and MediHoney, which are routinely used to treat chronic wounds. The efficacy of this treatment strategy was determined against biofilms of Escherichia coli formed on a plastic substratum and on a human keratinocyte monolayer substratum used as an in vitro biofilm-skin epithelial cell model. PAW pre-treatment greatly increased the killing efficacy of all the three antiseptics to eradicate the E. coli biofilms formed on the plastic and keratinocyte substrates. However, the efficacy of the combined PAW-antiseptic treatment and single treatments using PAW or antiseptic alone was lower for biofilms formed in the in vitro biofilm-skin epithelial cell model compared to the plastic substratum. Scavenging assays demonstrated that reactive species present within the PAW were largely responsible for its anti-biofilm activity. PAW treatment resulted in significant intracellular reactive oxygen and nitrogen species accumulation within the E. coli biofilms, while also rapidly acting on the microbial membrane leading to outer membrane permeabilisation and depolarisation. Together, these factors contribute to significant cell death, potentiating the antibacterial effect of the assessed antiseptics.

Sublethal Exposure to Plasma-Activated Water Influences the Morphological Characteristics, Phagocytic Ability, and Virulence of Acanthamoeba castellanii

PURPOSE

This study aimed to examine the ultrastructure, cytotoxicity, phagocytosis, and antioxidant responses of Acanthamoeba castellanii trophozoites exposed to sublethal plasma-activated water.

METHODS

Trophozoites were exposed to a sublethal treatment of PAW and compared to untreated viable trophozoites via adhesion assays on macrophage monolayers, osmo- and thermotolerance tests. Bacterial uptake was assessed in treated cells to evaluate their phagocytic characteristics. Oxidative stress biomarkers and antioxidant activities were compared in treated and untreated trophozoites. Finally, the expression of the mannose-binding protein (MBP), cysteine protease 3 (CP3), and serine endopeptidase (SEP) genes was determined in cells.

RESULTS

In PAW-treated trophozoites, cytopathic effects were more extensive and resulted in the detachment of macrophage monolayers. Treated trophozoites could not grow at high temperatures (43 °C). Moreover, they showed osmotolerance to 0.5 M D-mannitol but not to 1 M. Results demonstrated a higher bacterial uptake rate by PAW-treated trophozoites than untreated cells. Activities of superoxide dismutase and catalase and catalase were significantly greater in the treated trophozoites, and the glutathione and glutathione/glutathione disulfide were significantly lower in the PAW-treated cells. Exposure to PAW also significantly increased the malondialdehyde level and total antioxidant capacity. Treatment with PAW led to significantly higher expression of virulent genes like MBP, CP3, and SEP.

CONCLUSION

PAW is a double-edged sword against A. castellanii. PAW is an effective antiamoebic agent in proper usage, whereas its sublethal exposure may reduce its effectiveness and increase amoebas' pathogenicity. An agent's adequate concentration and exposure time are essential to achieve optimum results.

Effect of Dielectric Barrier Discharge Plasma against Listeria monocytogenes Mixed-Culture Biofilms on Food-Contact Surfaces

Listeria monocytogenes is a major foodborne pathogen. Various methods can be used to control biofilms formed by foodborne pathogens. Recently, the food industry has become interested in plasma, which can be used as a non-thermal technology with minimum changes to product quality. In this study, the effects of dielectric barrier discharge (DBD) plasma on L. monocytogenes mixed-culture biofilms formed on stainless steel (SS), latex hand glove (HG), and silicone rubber (SR) were investigated. DBD plasma effectuated reductions of 0.11-1.14, 0.28-1.27 and 0.37-1.55 log CFU/cm², respectively. Field emission scanning electron microscopy (FE-SEM) demonstrated that DBD plasma cuts off intercellular contact and induces cell decomposition to prevent the development of biological membranes. It was confirmed that the formed biofilms collapsed and separated into individual bacteria. Our findings suggest that DBD plasma can be used as an alternative non-heating sterilization technology in the food industry to reduce biofilm formation on bacterial targets.

Dry surface biofilms in the food processing industry: An overview on surface characteristics, adhesion and biofilm formation, detection of biofilms, and dry sanitization methods

Bacterial biofilm formation in low moisture food processing (LMF) plants is related to matters of food safety, production efficiency, economic loss, and reduced consumer trust. Dry surfaces may appear dry to the naked eye, however, it is common to find a coverage of thin liquid films and microdroplets, known as microscopic surface wetness (MSW). The MSW may favor dry surface biofilm (DSB) formation. DSB formation is similar in other industries, it occurs through the processes of adhesion, production of extracellular polymeric substances, development of microcolonies and maturation, it is mediated by a quorum sensing (QS) system and is followed by dispersal, leading to disaggregation. Species that survive on dry surfaces develop tolerance to different stresses. DSB are recalcitrant and contribute to higher resistance to sanitation, becoming potential sources of contamination, related to the spoilage of processed products and foodborne disease outbreaks. In LMF industries, sanitization is performed using physical methods without the presence of water. Although alternative dry sanitizing methods can be efficiently used, additional studies are still required to develop and assess the effect of emerging technologies, and to propose possible combinations with traditional methods to enhance their effects on the sanitization process. Overall, more information about the different technologies can help to find the most appropriate method/s, contributing to the development of new sanitization protocols. Thus, this review aimed to identify the main characteristics and challenges of biofilm management in low moisture food industries, and summarizes the mechanisms of action of different dry sanitizing methods (alcohol, hot air, UV-C light, pulsed light, gaseous ozone, and cold plasma) and their effects on microbial metabolism.

Technologies to decontaminate bacterial biofilm on hospital surfaces: a potential new role for cold plasma?

Healthcare-associated infections (HCAIs) are a major challenge and the near patient surface is important in harbouring causes such as methicillin-resistant Staphylococcus aureus (MRSA) and Clostridioides difficile. Current approaches to decontamination are sub-optimal and many studies have demonstrated that microbial causes of HCAIs may persist with onward transmission. This may be due to the capacity of these microbes to survive in biofilms on surfaces. New technologies to enhance hospital decontamination may have a role in addressing this challenge. We have reviewed current technologies such as UV light and hydrogen peroxide and also assessed the potential use of cold atmospheric pressure plasma (CAPP) in surface decontamination. The antimicrobial mechanisms of CAPP are not fully understood but the production of reactive oxygen and other species is believed to be important. CAPP systems have been shown to partially or completely remove a variety of biofilms including those caused by Candida albicans, and multi-drug-resistant bacteria such as MRSA. There are some studies that suggest promise for CAPP in the challenge of surface decontamination in the healthcare setting. However, further work is required to define better the mechanism of action. We need to know what surfaces are most amenable to treatment, how microbial components and the maturity of biofilms may affect successful treatment, and how would CAPP be used in the clinical setting.

Non-Invasive Physical Plasma for Preventing Radiation Dermatitis in Breast Cancer: A First-In-Human Feasibility Study

Radiation dermatitis (RD) is the most common acute side effect of breast irradiation. More than a century following the therapeutic utilisation of X-rays, potent preventative and therapeutic options are still lacking. Non-invasive physical plasma (NIPP) is an emerging approach towards treatment of various dermatological disorders. In this study, we sought to determine the safety and feasibility of a NIPP device on RD. Thirty patients undergoing hypofractionated whole-breast irradiation were included. Parallel to radiation treatment, the irradiated breast was treated with NIPP with different application regimens. RD was assessed during and after NIPP/radiation, using clinician- and patient-reported outcomes. Additionally, safety and feasibility features were recorded. None of the patients was prescribed topical corticosteroids and none considered the treatment to be unpleasant. RD was less frequent and milder in comparison with standard skin care. Neither NIPP-related adverse events nor side effects were reported. This proven safety and feasibility profile of a topical NIPP device in the prevention and treatment of RD will be used as the framework for a larger intrapatient-randomised double-blind placebo-controlled trial, using objective and patient-reported outcome measures as an endpoint.

Microbial Quality of Liquid Feed for Pigs and Its Impact on the Porcine Gut Microbiome

Simple Summary

Liquid feed is produced by mixing dry feed ingredients with water, and sometimes liquid co-products from the food and beverage industry, at a defined ratio. Liquid feeding of pigs is popular, particularly in parts of northern and western Europe, and can be associated with lower feed costs, improved dry matter intake, growth rate and gut health, compared to dry feeding. However, spontaneous/uncontrolled fermentation upon mixing of feed with water or co-products can decrease the microbial and nutritional quality of the feed, resulting in poorer pig health and growth. For this reason, strategies aimed at optimising liquid feed microbial quality are frequently employed. These include: deliberate fermentation with/without the use of lactic acid bacteria starter cultures that produce lactic acid and lower the feed pH, thereby preventing growth of pathogens. Fermenting only the cereal component of the diet is preferred to whole diet fermentation to minimise loss of free amino acids from the diet during fermentation. This review examines the microbiome of liquid feed and explores how optimisation strategies impact both feed microbial quality and the gut microbiota and growth of liquid-fed pigs. It also covers cleaning and disinfection of liquid feeding systems and how this might impact liquid feed microbial quality.

Abstract

There is evidence that spontaneous fermentation frequently occurs in liquid pig feed that is intended to be delivered as fresh liquid feed, often with a resultant deterioration in the microbial and nutritional quality of the feed, which can negatively affect pig health and growth. Strategies including controlled fermentation with microbial inoculants, pre-fermentation or soaking of the cereal fraction of the diet, enzyme supplementation and dietary acidification have been employed to inhibit pathogens and prevent deterioration of feed nutritional quality, with promising results obtained in many cases. This review evaluates the impact of these strategies on the microbial quality of liquid feed and discusses how they can be further improved. It also investigates if/how these strategies impact the pig gut microbiota and growth performance of liquid-fed pigs. Finally, we review liquid feed system sanitisation practices, which are highly variable from farm to farm and discuss the impact of these practices and whether they are beneficial or detrimental to liquid feed microbial quality. Overall, we provide a comprehensive review of the current state of knowledge on liquid feed for pigs, focusing on factors affecting microbial quality and strategies for its optimisation, as well as its impact on the pig gut microbiome.

Inactivation of Staphylococcus aureus and Escherichia coli Biofilms by Air-Based Atmospheric-Pressure DBD Plasma

Air-based atmospheric-pressure plasma is an effective non-thermal method in deactivating various kinds of microbial biofilms with several advantages, including high bactericidal efficiency and low treatment costs. Bacterial biofilm formation is a major determinant in establishment of bacterial infection and also resistance to antibacterial chemotherapy. This study aims to assess the anti-biofilm potential of air-based atmospheric-pressure DBD plasma against Staphylococcus aureus and Escherichia coli biofilms. The biofilms of Staphylococcus aureus and Escherichia coli were exposed to air-based atmospheric-pressure DBD plasma for up to 4 min (control, 30 s, 90 s, 3 min, and 4 min) and their biofilm formation level, viability, and membrane integrity were determined. Based on the results, plasma exposure caused disruption up to 70% and 85% for S. aureus and E. coli biofilms, respectively. The biofilm disruption potential of air-based atmospheric-pressure DBD plasma was confirmed using the scanning electron microscopy (SEM). Besides, based on confocal laser scanning microscopy (CLSM), plasma exposure caused a significant bacterial inactivation and E. coli was found as more susceptible strain than S. aureus. In conclusion, atmospheric-pressure DBD plasma could be considered an efficient non-thermal approach against bacterial pathogenicity by biofilm disruption and thus prevention of infection establishment.

Response of Controlled Cell Load Biofilms to Cold Atmospheric Plasma Jet: Evidence of Extracellular Matrix Contribution

Aim: Study of the biocidal effect of a cold atmospheric-pressure plasma in ambient air on single-species bacterial biofilms with controlled cell density, characterized by different extracellular matrices. Methods and results: Two bacterial strains were chosen to present different Gram properties and contrasted extracellular matrices: Pseudomonas aeruginosa ATCC 15442 (Gram-negative), and Leuconostoc citreum NRRL B-1299 (Gram-positive). P. aeruginosa biofilm exhibits a complex matrix, rich in proteins while L. citreum presents the specificity to produce glucan-type exopolysaccharides when grown in the presence of sucrose. Plasma was applied on both surface-spread cells and 24-h grown biofilms with controlled cell loads over 5, 10, or 20 min. Surface-spread bacteria showed a time dependent response, with a maximal bacterial reduction of 2.5 log after 20 min of treatment. On the other hand, in our experimental conditions, no bactericidal effect could be observed when treating biofilms of P. aeruginosa and glucan-rich L. citreum. Conclusions: For biofilms presenting equivalent cell loads, the response to plasma treatment seemed to depend on the properties of the extracellular matrix characterized by infrared spectroscopy, scanning electron microscopy, or dry weight. Significance and impact of study: Both cell load standardization and biofilm characterization are paramount factors to consider the biocide effect of plasma treatments. The extracellular matrix could affect the plasma efficacy by physical and/or chemical protective effects.

Applications of Cold Atmospheric Pressure Plasma in Dentistry

Plasma is an electrically conducting medium that responds to electric and magnetic fields. It consists of large quantities of highly reactive species, such as ions, energetic electrons, exited atoms and molecules, ultraviolet photons, and metastable and active radicals. Non-thermal or cold plasmas are partially ionized gases whose electron temperatures usually exceed several tens of thousand degrees K, while the ions and neutrals have much lower temperatures. Due to the presence of reactive species at low temperature, the biological effects of non-thermal plasmas have been studied for application in the medical area with promising results. This review outlines the application of cold atmospheric pressure plasma (CAPP) in dentistry for the control of several pathogenic microorganisms, induction of anti-inflammatory, tissue repair effects and apoptosis of cancer cells, with low toxicity to healthy cells. Therefore, CAPP has potential to be applied in many areas of dentistry such as cariology, periodontology, endodontics and oral oncology.

Yeasts in Liquid Swine Diets: Identification Methods, Growth Temperatures and Gas-Formation Potential

Liquid feed is susceptible to microbiological growth. Yeasts are said to cause sudden death in swine due to intestinal gas formation. As not all animals given high yeast content feed fall ill, growth and gas formation potential at body temperature were investigated as possible causally required properties. The best identification method for these environmental yeasts should be tested beforehand. Yeasts derived from liquid diets without (LD - S) and liquid diets with maize silage (LD + S) were examined biochemically (ID32C-test) and with MALDI-TOF with direct smear (DS) and an extraction method (EX). Growth temperature and gas-forming potential were measured. With MALDI-EX, most yeast isolates were identified: Candida krusei most often in LD - S, and C. lambica most often in LD + S, significantly more than in LD - S. Larger colonies, 58.75% of all yeast isolates, were formed at 25 °C rather than at 37 °C; 17.5% of all isolates did not grow at 37 °C at all. Most C. krusei isolates formed high gas amounts within 24 h, whereas none of the C. lambica, C. holmii and most other isolates did. The gas pressure formed by yeast isolates varied more than tenfold. Only a minority of the yeasts were able to produce gas at temperatures common in the pig gut.

Combination of non-thermal plasma and subsequent antibiotic treatment for biofilm re-development prevention

The influence of non-thermal plasma (NTP) treatment on the prevention of antibiotic resistance of microbial biofilms was studied. Staphylococcus epidermidis and Escherichia coli bacteria and a yeast Candida albicans, grown on the surface of Ti-6Al-4V alloy used in the manufacture of prosthetic implants, were employed. Their biofilms were exposed to NTP produced by DC cometary discharge and subsequently treated with antibiotics commonly used for the treatment of infections caused by them: erythromycin (ERY), polymyxin B (PMB), or amphotericin B (AMB), respectively. All biofilms displayed significant reduction of their metabolic activity after NTP exposure, the most sensitive was S. epidermidis. The subsequent action of antibiotics caused significant decrease in the metabolic activity of S. epidermidis and E. coli, but not C. albicans, although the area covered by biofilm decreased in all cases. The combined effect of NTP with antibiotics was thus proved to be a promising strategy in bacterial pathogen treatment.

Influence of Plasma Characteristics on the Inactivation Mechanism of Cold Atmospheric Plasma (CAP) for Listeria monocytogenes and Salmonella Typhimurium Biofilms

This research aimed to take a next step towards unravelling the CAP inactivation mechanism for mature (Listeria monocytogenes (Gram positive) and Salmonella Typhimurium (Gram negative)) model biofilms, which will support the further optimization this novel technology. More specifically, we examined how the inactivation mechanism was influenced by the applied processing conditions, i.e., by the electrode configuration, the composition of the gas flow, and the power of the discharge. For each combination of plasma characteristics, we examined if the applied CAP treatment had an effect on (i) the cell membrane, (ii) the intracellular DNA, and (iii) the EPS matrix. In addition, we assessed which (reactive) CAP species were responsible for this lethal/damaging effect and whether these species were able to diffuse into the deeper layers of the biofilms. The results indicated that the inactivation mechanism was indeed influenced by the applied processing conditions. Nevertheless, the bactericidal effect of CAP was always a combination of both damage to the membrane and the DNA, caused by (i) the generation of (intracellular) ROS and RNS, (ii) a drop in pH, and/or (iii) the potential generation of a small amount of UV photons. Moreover, the plasma species were able to penetrate into the deeper layers of the model biofilms and some treatment conditions resulted in an increased biofilm porosity.

Combined Effect of Cold Atmospheric Plasma and Hydrogen Peroxide Treatment on Mature Listeria monocytogenes and Salmonella Typhimurium Biofilms

Cold Atmospheric Plasma (CAP) is a promising novel method for biofilm inactivation as log-reduction values up to 4.0 log10 (CFU/cm2) have been reported. Nevertheless, as the efficacy of CAP itself is not sufficient for complete inactivation of mature biofilms, the hurdle technology could be applied in order to obtain higher combined efficacies. In this study, CAP treatment was combined with a mild hydrogen peroxide (H2O2) treatment for disinfection of 1 and 7 day(s) old Listeria monocytogenes and Salmonella Typhimurium biofilms. Three different treatment sequences were investigated in order to determine the most effective treatment sequence, i.e., (i) first CAP, then H2O2, (ii) first H2O2, then CAP, and (iii) a simultaneous treatment of CAP and H2O2. Removal of the biofilm, induction of sub-lethal injury, and H2O2 breakdown due to the presence of catalase within the biofilms were investigated in order to comment on their possible contribution to the combined inactivation efficacy. Results indicated that the preferred treatment sequence was dependent on the biofilm forming species, biofilm age, and applied H2O2 concentration [0.05 or 0.20% (v/v)]. At the lowest H2O2 concentration, the highest log-reductions were generally observed if the CAP treatment was preceded by the H2O2 treatment, while at the highest H2O2 concentration, the opposite sequence (first CAP, then H2O2) proved to be more effective. Induction of sub-lethal injury contributed to the combined bactericidal effect, while the presence of catalase within the biofilms resulted in an increased resistance. In addition, high log-reductions were partially the result of biofilm removal. The highest overall log-reductions [i.e., up to 5.42 ± 0.33 log10 (CFU/cm2)] were obtained at the highest H2O2 concentration if CAP treatment was followed by H2O2 treatment. As this resulted in almost complete inactivation of the L. monocytogenes and S. Typhimurium biofilms, the combined treatment of CAP and H2O2 proved to be a promising method for disinfection of abiotic surfaces.

Dual-Species Model Biofilm Consisting of Listeria monocytogenes and Salmonella Typhimurium: Development and Inactivation With Cold Atmospheric Plasma (CAP)

Most environmental biofilms contain a variety of species. These species can establish cooperative and competitive interactions, possibly resulting in an increase or a decrease in antimicrobial resistance. Therefore, results obtained following inactivation of single-species biofilms by means of different technologies (e.g., Cold Atmospheric Plasma, CAP) should be validated for multi-species biofilms. First, a strongly adherent and mature Listeria monocytogenes and S. Typhimurium dual-species biofilm was developed by altering different incubation conditions, i.e., growth medium, incubation temperature, inoculum ratio of L. monocytogenes and S. Typhimurium cells, and incubation time. Adherence and maturity were quantified by means of optical density measurements and viable plate counts, respectively. Secondly, both the (1 day old) reference biofilm and a more mature 7 days old biofilm were treated for different CAP treatment times (0-30 min). Viable plate counts were again used to determine the (remaining) cell density. For both the biofilm development and inactivation, predictive models were applied to describe the growth/inactivation kinetics. Finally, the kinetics of the [1 and 7 day(s) old] dual-species biofilms were compared with those obtained for the corresponding single-species biofilms. Results implied that a strongly adherent and mature reference dual-species biofilm was obtained following 24 h of incubation at 25°C using 20-fold diluted TSB and an inoculum ratio of 1:1. Main observations regarding CAP inactivation were: (i) the dual-species biofilm age had no influence on the CAP efficacy, although a longer treatment time was required for the oldest biofilm, (ii) for the 1 day old biofilms, CAP treatment became less efficient for S. Typhimurium inactivation when this species was part of the dual-species biofilm, while L. monocytogenes inactivation was not influenced by the biofilm type, and (iii) for the 7 days old biofilms, CAP inactivation of both species became more efficient when they were part of the dual-species biofilms. It can be concluded that the efficacy of the CAP treatment is altered when cells become part of a dual-species biofilm, which is quite important with respect to a possible application of CAP for biofilm inactivation within the food industry.

Application of Non-Thermal Plasma on Biofilm: A Review

The formation of bacterial biofilm on implanted devices or damaged tissues leads to biomaterial-associated infections often resulting in life-threatening diseases and implant failure. It is a challenging process to eradicate biofilms as they are resistant to antimicrobial treatments. Conventional techniques, such as high heat and chemicals exposure, may not be suitable for biofilm removal in nosocomial settings. These techniques create surface degradation on the treated materials and lead to environmental pollution due to the use of toxic chemicals. A novel technique known as non-thermal plasma has a great potential to decontaminate or sterilize those nosocomial biofilms. This article aims to provide readers with an extensive review of non-thermal plasma and biofilms to facilitate further investigations. A brief introduction summarizes the problem caused by biofilms in hospital settings with current techniques used for biofilm inactivation followed by the literature review strategy. The remainder of the review discusses plasma and its generation, the role played by plasma reactive species, various factors affecting the antimicrobial efficacy of non-thermal plasma and summarizes many studies published in the field.

The Pseudomonas aeruginosa biofilm matrix and cells are drastically impacted by gas discharge plasma treatment: A comprehensive model explaining plasma-mediated biofilm eradication

Biofilms are microbial communities encased in a protective matrix composed of exopolymeric substances including exopolysaccharides, proteins, lipids, and extracellular DNA. Biofilms cause undesirable effects such as biofouling, equipment damage, prostheses colonization, and disease. Biofilms are also more resilient than free-living cells to regular decontamination methods and therefore, alternative methods are needed to eradicate them. The use of non-thermal atmospheric pressure plasmas is a good alternative as plasmas contain reactive species, free radicals, and UV photons well-known for their decontamination potential against free microorganisms. Pseudomonas aeruginosa biofilms colonize catheters, indwelling devices, and prostheses. Plasma effects on cell viability have been previously documented for P. aeruginosa biofilms. Nonetheless, the effect of plasma on the biofilm matrix has received less attention and there is little evidence regarding the changes the matrix undergoes. The aim of this work was to study the effect plasma exerts mostly on the P. aeruginosa biofilm matrix and to expand the existing knowledge about its effect on sessile cells in order to achieve a better understanding of the mechanism/s underlying plasma-mediated biofilm inactivation. We report a reduction in the amount of the biofilm matrix, the loss of its tridimensional structure, and morphological changes in sessile cells at long exposure times. We show chemical and structural changes on the biofilm matrix (mostly on carbohydrates and eDNA) and cells (mostly on proteins and lipids) that are more profound with longer plasma exposure times. We also demonstrate the presence of lipid oxidation products confirming cell membrane lipid peroxidation as plasma exposure time increases. To our knowledge this is the first report providing detailed evidence of the variety of chemical and structural changes that occur mostly on the biofilm matrix and sessile cells as a consequence of the plasma treatment. Based on our results, we propose a comprehensive model explaining plasma-mediated biofilm inactivation.

Cold atmospheric plasma ameliorates imiquimod-induced psoriasiform dermatitis in mice by mediating antiproliferative effects

Psoriasis is a chronic hyperproliferative skin disease characterised by excessive growth of keratinocytes. Indeed, inducing keratinocyte apoptosis is a key mechanism responsible for psoriatic plaques clearance following some important existing therapies, which display pro-oxidant activity. Cold atmospheric plasma (CAP), acting as a tuneable source of reactive oxygen and nitrogen species (RONS), can controllably transfer RONS to the cellular environment, deliver antiproliferative RONS concentrations and exert antiproliferative and proapoptotic effects. This study was undertaken to evaluate the therapeutic potential of CAP in psoriasis. We used cell models of psoriasis-like inflammation by adding lipopolysaccharide (LPS) or tumour necrosis factor alpha (TNF-α) to HaCaT keratinocytes. Indirect plasma, plasma-activated medium (PAM), was administered to HaCaT cells. Atmospheric pressure plasma jet (APPJ) was applied directly to imiquimod (IMQ)-induced psoriasiform dermatitis in mice. The results showed that PAM induced an increase in intracellular ROS and caused keratinocyte apoptosis. Moreover, cells under inflammation showed lesser viability and larger apoptosis rate. With repeated administration of APPJ, psoriasiform lesions showed ameliorated morphological manifestation and reduced epidermal proliferation. Overall, this study supports that CAP holds good potential in psoriasis treatment.

Biofilms in Food Processing Environments: Challenges and Opportunities

This review examines the impact of microbial communities colonizing food processing environments in the form of biofilms on food safety and food quality. The focus is both on biofilms formed by pathogenic and spoilage microorganisms and on those formed by harmless or beneficial microbes, which are of particular relevance in the processing of fermented foods. Information is presented on intraspecies variability in biofilm formation, interspecies relationships of cooperativism or competition within biofilms, the factors influencing biofilm ecology and architecture, and how these factors may influence removal. The effect on the biofilm formation ability of particular food components and different environmental conditions that commonly prevail during food processing is discussed. Available tools for the in situ monitoring and characterization of wild microbial biofilms in food processing facilities are explored. Finally, research on novel agents or strategies for the control of biofilm formation or removal is summarized.

Medically important biofilms and non-thermal plasma

In recent decades, the non-thermal plasma, i.e. partially or completely ionized gas produced by electric discharges at ambient temperature, has become of interest for its microbiocidal properties with potential of use in the food industry or medicine. Recently, this interest focuses not only on the planktonic forms of microorganisms but also on their biofilms. The works in this interdisciplinary field are summarized in this review. The wide range of biofilm-plasma interactions is divided into studies of general plasma action on bacteria, on biofilm and on its oral and dental application; a short overview of plasma instrumentation is also included. In addition, not only biofilm combating but also an important area of biofilm prevention is discussed. Various DC discharges of the point-to-plane type. Author's photograph, published in Khun et al. (Plasma Sources Sci Technol 27:065002, 2018).

Cold Plasma for Effective Fungal and Mycotoxin Control in Foods: Mechanisms, Inactivation Effects, and Applications

Cold plasma treatment is a promising intervention in food processing to boost product safety and extend the shelf-life. The activated chemical species of cold plasma can act rapidly against micro-organisms at ambient temperatures without leaving any known chemical residues. This review presents an overview of the action of cold plasma against molds and mycotoxins, the underlying mechanisms, and applications for ensuring food safety and quality. The cold plasma species act on multiple sites of a fungal cell resulting in loss of function and structure, and ultimately cell death. Likewise, the species cause chemical breakdown of mycotoxins through various pathways resulting in degradation products that are known to be less toxic. We argue that the preliminary reports from cold plasma research point at good potential of plasma for shelf-life extension and quality retention of foods. Some of the notable food sectors which could benefit from antimycotic and antimycotoxin efficacy of cold plasma include, the fresh produce, food grains, nuts, spices, herbs, dried meat and fish industries.

Contribution of Fluorescence Techniques in Determining the Efficiency of the Non-thermal Plasma Treatment

We have recently developed a non-thermal plasma (NTP) equipment intended to sterilize fragile medical devices and maintain the sterile state of items downstream the treatment. With traditional counts on agar plate a six log reduction of Staphylococcus aureus viability was obtained within 120 min of O₂, Ar, or N₂ NTP treatments. However to determine the best NTP process, we studied the different physiological states of S. aureus by flow cytometry (FC) and confocal laser scanning microscopy (CLSM) focusing on the esterasic activity and membrane integrity of the bacteria. Two fluorochromes, 5-(and-6)-carboxy-2^',7^'-dichlorofluorescein diacetate and propidium iodide were used in order to distinguish three sub-populations: metabolically active, permeabilized, and damaged bacteria that can be in the viable but nonculturable state. FC and CLSM highlight that O₂ and Ar NTP treatments were the most attractive processes. Indeed, a 5 min of Ar NTP generated a high destruction of the structure of bacteria and a 120 min of O₂ NTP treatment led to the higher decrease of the total damaged bacteria population. SEM observations showed that in presence of clusters, bacteria of upper layers are easily altered compared to bacteria in the deeper layers. In conclusion, the plate counting method is not sufficient by itself to determine the best NTP treatment. FC and CLSM represent attractive indicator techniques to select the most efficient gas NTP treatment generating the lowest proportion of viable bacteria and the most debris.

Cold Plasmas for Biofilm Control: Opportunities and Challenges

Bacterial biofilm infections account for a major proportion of chronic and medical device associated infections in humans, yet our ability to control them is compromised by their inherent tolerance to antimicrobial agents. Cold atmospheric plasma (CAP) represents a promising therapeutic option. CAP treatment of microbial biofilms represents the convergence of two complex phenomena: the production of a chemically diverse mixture of reactive species and intermediates, and their interaction with a heterogeneous 3D interface created by the biofilm extracellular polymeric matrix. Therefore, understanding these interactions and physiological responses to CAP exposure are central to effective management of infectious biofilms. We review the unique opportunities and challenges for translating CAP to the management of biofilms.

Human teeth biobank: Microbiological analysis of the teeth storage solution

The cross-infections may occur during handling of dental elements, affecting the health of dental practitioners and researchers. This study aimed to analyze the influence of the storage medium temperature on the bacterial contingent of the human teeth used for research purposes. Thirty human teeth were donated to the Human Teeth Biobank immediately after extraction. The teeth were cleaned with tap water and neutral soap. The teeth were randomly distributed according to the temperature of the storage solution (deionized water): at 4 °C (refrigerator) or at -10 °C (freezer) and were stored individually in sterile vials during 60 days. After this period, a microbiological analysis (CFU/mL) of the storage solutions was performed and teeth were submitted to SEM analysis. Data were analyzed by Kruskal-Wallis test followed by Dunn's post-test (p ≤ .05). Total aerobic bacteria ranged from 5.8 to 8.4 log₁₀ CFU/mL for refrigerated solution and from 1.9 to 8.5 log₁₀ CFU/mL for frozen solution. No statistical differences were found between the storage solutions (p > .05). The counts of Streptococcus spp., Lactobacillus spp., and Staphylococcus spp. were similar for both storage solutions (p > .05). SEM analysis showed spiral- and rod-shaped bacteria attached on teeth stored under 4 °C, which may suggest the presence of Treponema spp. and Lactobacillus spp. Similar morphological forms were found on teeth stored under -10 °C. A biofilm organized in honeycomb-like form was found in the frozen teeth. Cocci were eventually found in all the samples. It was concluded that bacterial growth and survival were not influenced by the temperature of the teeth storage solution.

Medical applications of nonthermal atmospheric pressure plasma in dermatology

Plasma is an ionized gas that consists of positively and negatively charged particles, neutral atoms, and photons. Recent developments in plasma sources have made it possible to generate room-temperature plasma in the "open air", thus enabling the application of plasma in vivo. Using nonthermal plasma, active agents can be efficiently delivered to target cells without creating thermal damage. Also known as cold atmospheric pressure plasma (CAP), nonthermal atmospheric pressure plasma offers innovative medical applications. In this context, it has also gained wide attention in the field of dermatology. The complex and variable mixture of active agents in plasma - predominantly reactive oxygen and nitrogen species (ROS, RNS) - can control or trigger complex biochemical reactions, achieving the desired effects in a dose-dependent manner. The objective of the present review is to present potential applications of plasma in dermatology and analyze its potential mechanisms of action.