Modelling of inactivation kinetics of Escherichia coli, Salmonella Enteritidis and Bacillus subtilis treated with a multi-hollow surface dielectric barrier discharge plasma.

The efficacy of multi-hollow surface dielectric barrier discharge treatment against Escherichia coli, Salmonella Enteritidis and Bacillus subtilis was studied. Ambient air, O2, and N2 were used as working gas with a flow rate of 6 l/m. Power delivered into plasma was 30 W over an area of 2 × 2 cm2. The active species in plasma generated in different gases participating in the inactivation of microorganisms were evaluated by optical emission spectroscopy and Fourier transform infrared spectroscopy. Inactivation curves were fitted to the Bigelow log-linear, the biphasic, and Geeraerd models. According to the results, all plasma treatments inactivated tested microorganisms, depending on a working gas. The most sensitivity of bacteria was observed to the ambient air plasma. Inactivation up to 5 log for E. coli and S. Enteritidis could be achieved within 15 s of plasma treatment. Air plasma exposure of 25 s also led to log10 CFU/ml of B. subtilis from 7.98 to 4.39. S. Enteritidis was slight resistance to plasma treatment with N2. Within 180 s nitrogen plasma treatment, a 2.04 log10 CFU/ml reduction was recorded.

Non-thermal plasma induces changes in aflatoxin production, devitalization, and surface chemistry of Aspergillus parasiticus.

Non-thermal plasma (NTP) represents the fourth state of matter composed of neutral molecules, atoms, ions, radicals, and electrons. It has been used by various industries for several decades, but only recently NTPs have emerged in fields such as medicine, agriculture, and the food industry. In this work, we studied the effect of NTP exposure on aflatoxin production, conidial germination and mycelial vitality, morphological and surface changes of conidia and mycelium. When compared with colonies grown from untreated conidia, the colonies from NTP-treated conidia produced significantly higher levels of aflatoxins much earlier during development than colonies from untreated conidia. However, at the end of cultivation, both types of cultures yielded similar aflatoxin concentrations. The increase in the accumulation of aflatoxins was supported by high transcription levels of aflatoxin biosynthetic genes, which indicated a possibility that NTP treatment of conidia was having a longer-lasting effect on colony development and aflatoxins accumulation. NTP generated in the air at atmospheric pressure effectively devitalized Aspergillus parasiticus in conidia and hyphae within a few minutes of treatment. To describe devitalization kinetics, we applied Weibull and Hill models on sets of data collected at different exposure times during NTP treatment. The damage caused by NTP to hyphal cell wall structures was displayed by raptures visualized by scanning electron microscopy. Fourier transform infrared spectroscopy demonstrated that changes in cell envelope correlated with shifts in characteristic chemical bonds indicating dehydration, oxidation of lipids, proteins, and polysaccharides. Key points • Non-thermal plasma increases aflatoxin production shortly after treatment. • Non-thermal plasma rapidly devitalizes Aspergillus parasiticus. • Non-thermal plasma disrupts the cell surface and oxidizes biological components.

Surface Characterization and Anti-Biofilm Effectiveness of Hybrid Films of Polyurethane Functionalized with Saponite and Phloxine B.

The main objective of this work was to synthesize composites of polyurethane (PU) with organoclays (OC) exhibiting antimicrobial properties. Layered silicate (saponite) was modified with octadecyltrimethylammonium cations (ODTMA) and functionalized with phloxine B (PhB) and used as a filler in the composites. A unique property of composite materials is the increased concentration of modifier particles on the surface of the composite membranes. Materials of different compositions were tested and investigated using physico-chemical methods, such as infrared spectroscopy, X-ray diffraction, contact angle measurements, absorption, and fluorescence spectroscopy in the visible region. The composition of an optimal material was as follows: nODTMA/mSap = 0.8 mmol g-1 and nPhB/mSap = 0.1 mmol g-1. Only about 1.5% of present PhB was released in a cultivation medium for bacteria within 24 h, which proved good stability of the composite. Anti-biofilm properties of the composite membranes were proven in experiments with resistant Staphylococcus aureus. The composites without PhB reduced the biofilm growth 100-fold compared to the control sample (non-modified PU). The composite containing PhB in combination with the photodynamic inactivation (PDI) reduced cell growth by about 10,000-fold, thus proving the significant photosensitizing effect of the membranes. Cell damage was confirmed by scanning electron microscopy. A new method of the synthesis of composite materials presented in this work opens up new possibilities for targeted modification of polymers by focusing on their surfaces. Such composite materials retain the properties of the unmodified polymer inside the matrix and only the surface of the material is changed. Although these unique materials presented in this work are based on PU, the method of surface modification can also be applied to other polymers. Such modified polymers could be useful for various applications in which special surface properties are required, for example, for materials used in medical practice.

Cold Atmospheric Pressure Plasma Treatment of Maize Grains-Induction of Growth, Enzyme Activities and Heat Shock Proteins.

Zea mays L. is one of the most produced crops, and there are still parts of the world where maize is the basic staple food. To improve agriculture, mankind always looks for new, better methods of growing crops, especially in the current changing climatic conditions. Cold atmospheric pressure plasma (CAPP) has already showed its potential to enhance the culturing of crops, but it still needs more research for safe implementation into agriculture. In this work, it was shown that short CAPP treatment of maize grains had a positive effect on the vitality of grains and young seedlings, which may be connected to stimulation of antioxidant and lytic enzyme activities by short CAPP treatment. However, the prolonged treatment had a negative impact on the germination, growth, and production indexes. CAPP treatment caused the increased expression of genes for heat shock proteins HSP101 and HSP70 in the first two days after sowing. Using comet assay it was observed that shorter treatment times (30-120 s) did not cause DNA damage. Surface diagnostics of plasma-treated grains showed that plasma increases the hydrophilicity of the surface but does not damage the chemical bonds on the surface.

The Effects of Cold Atmospheric Pressure Plasma on Germination Parameters, Enzyme Activities and Induction of DNA Damage in Barley.

Climate change, environmental pollution and pathogen resistance to available chemical agents are part of the problems that the food industry has to face in order to ensure healthy food for people and livestock. One of the promising solutions to these problems is the use of cold atmospheric pressure plasma (CAPP). Plasma is suitable for efficient surface decontamination of seeds and food products, germination enhancement and obtaining higher yields in agricultural production. However, the plasma effects vary due to plasma source, treatment conditions and seed type. In our study, we tried to find the proper conditions for treatment of barley grains by diffuse coplanar surface barrier discharge, in which positive effects of CAPP, such as enhanced germination or decontamination effects, would be maximized and harmful effects, such as oxidation and genotoxic potential, minimized. Besides germination parameters, we evaluated DNA damage and activities of various germination and antioxidant enzymes in barley seedlings. Plasma exposure resulted in changes in germination parameters and enzyme activities. Longer exposures had also genotoxic effects. As such, our findings indicate that appropriate plasma exposure conditions need to be carefully optimized in order to preserve germination, oxidation balance and genome stability, should CAPP be used in agricultural practice.

Physico-Chemical Characterization and Antimicrobial Properties of Hybrid Film Based on Saponite and Phloxine B.

This research was aimed at the preparation of a hybrid film based on a layered silicate saponite (Sap) with the immobilized photosensitizer phloxine B (PhB). Sap was selected because of its high cation exchange capacity, ability to exfoliate into nanolayers, and to modify different surfaces. The X-ray diffraction of the films confirmed the intercalation of both the surfactant and PhB molecules in the Sap film. The photosensitizer retained its photoactivity in the hybrid films, as shown by fluorescence spectra measurements. The water contact angles and the measurement of surface free energy demonstrated the hydrophilic nature of the hybrid films. Antimicrobial effectiveness, assessed by the photodynamic inactivation on hybrid films, was tested against a standard strain and against methicillin-resistant bacteria of Staphylococcus aureus (MRSA). One group of samples was irradiated (green LED light; 2.5 h) and compared to nonirradiated ones. S. aureus strains manifested a reduction in growth from 1-log10 to over 3-log10 compared to the control samples with Sap only, and defects in S. aureus cells were proven by scanning electron microscopy. The results proved the optimal photo-physical properties and anti-MRSA potential of this newly designed hybrid system that reflects recent progress in the modification of surfaces for various medical applications.

The effect of cold atmospheric pressure plasma on Aspergillus ochraceus and ochratoxin A production.

Aspergillus ochraceus is a soil fungus known to produce ochratoxin A, a harmful secondary metabolite. Prevention and control of fungal pathogens mostly rely on chemical fungicides, which is one of the contributing factors in the emergence of the fungal resistance, hence novel methods for fungal eradication have been extensively researched. The cold atmospheric pressure (CAP) plasma generated in ambient air has been recently applied in microbial decontamination. Here we used the diffuse coplanar surface barrier discharge in inactivation of a toxigenic strain A. ochraceus. The plasma-treated conidia and mycelium exhibited morphological changes such as ruptures and desiccation. Mycelium dehydration and changes in the chemical composition of hyphal surface accompanied plasma treatment. The growth of 26 h old mycelia were significantly restricted after 30 s of plasma treatment. The conidial vitality declined 4 logs after 180 s of plasma exposure leading to almost complete decontamination. After shorter plasma treatment of conidia, the ochratoxin A (OTA) production increased at the early stage of cultivation, but the overall level was significantly reduced compared to untreated samples after longer cultivation. Our results indicated that the fungal growth and the OTA production were significantly changed by plasma treatment and underscored CAP plasma as a promising method in the decontamination of A. ochraceus without a risk to generate strains with increased OTA production.

Technical applications of plasma treatments: current state and perspectives.

Rapidly evolving cold atmospheric pressure plasma (CAPP)-based technology has been actively used not only in bioresearch but also in biotechnology, food safety and processing, agriculture, and medicine. High variability in plasma device configurations and electrode layouts has accelerated non-thermal plasma applications in treatment of various biomaterials and surfaces of all sizes. Mode of cold plasma action is likely associated with synergistic effect of biologically active plasma components, such as UV radiation or reactive species. CAPP has been employed in inactivation of viruses, to combat resistant microorganisms (antibiotic resistant bacteria, spores, biofilms, fungi) and tumors, to degrade toxins, to modify surfaces and their properties, to increase microbial production of compounds, and to facilitate wound healing, blood coagulation, and teeth whitening. The mini-review provides a brief overview of non-thermal plasma sources and recent achievements in biological sciences. We have also included pros and cons of CAPP technologies as well as future directions in biosciences and their respective industrial fields.

Cold plasma treatment triggers antioxidative defense system and induces changes in hyphal surface and subcellular structures of Aspergillus flavus.

The cold atmospheric-pressure plasma (CAPP) has become one of the recent effective decontamination technologies, but CAPP interactions with biological material remain the subject of many studies. The CAPP generates numerous types of particles and radiations that synergistically affect cells and tissues differently depending on their structure. In this study, we investigated the effect of CAPP generated by diffuse coplanar surface barrier discharge on hyphae of Aspergillus flavus. Hyphae underwent massive structural changes after plasma treatment. Scanning electron microscopy showed drying hyphae that were forming creases on the hyphal surface. ATR-FTIR analysis demonstrated an increase of signal intensity for C=O and C-O stretching vibrations indicating chemical changes in molecular structures located on hyphal surface. The increase in membrane permeability was detected by the fluorescent dye, propidium iodide. Biomass dry weight determination and increase in permeability indicated leakage of cell content and subsequent death. Disintegration of nuclei and DNA degradation confirmed cell death after plasma treatment. Damage of plasma membrane was related to lipoperoxidation that was determined by higher levels of thiobarbituric acid reactive species after plasma treatment. The CAPP treatment led to rise of intracellular ROS levels detected by fluorescent microscopy using 2',7'-dichlorodihydrofluorescein diacetate. At the same time, antioxidant enzyme activities increased, and level of reduced glutathione decreased. The results in this study indicated that the CAPP treatment in A. flavus targeted both cell surface structures, cell wall, and plasma membrane, inflicting injury on hyphal cells which led to subsequent oxidative stress and finally cell death at higher CAPP doses.

Cold atmospheric pressure ambient air plasma inhibition of pathogenic bacteria on the surface of black pepper.

In present study, the inhibition effect of low temperature plasma on Bacillus subtilis, Escherichia coli, Salmonella Enteritidis and B. subtilis endospores inoculated on the surface of black peppercorns was studied. Plasma was generated by Diffuse Coplanar Surface Barrier Discharge (DCSBD) at atmospheric pressure in ambient air. Plasma treatment time of 300 s led to log10 CFU/g reduction of B. subtilis from 7.36 to 2.30 and B. subtilis endospores from 4.42 to 2.39. Plasma treatment reduced the number of E. coli and Salmonella Enteritidis to below detection level (1.0 log10 CFU/g) from initial populations of 7.45 log10 CFU/g and 7.60 log10 CFU/g, respectively. The inactivation kinetics was explained by Weibull model. Decimal reduction times (D-values) for B. subtilis, E. coli, Salmonella Enteritidis, and B. subtilis endospores were determined as 43 s, 47 s, 58 s, and 142 s, respectively. The surface morphology observed by Scanning Electron Microscopy showed no significant changes after the plasma treatment. The influence of plasma on chemical bonds on the surface and inside the peppercorns was studied by Attenuated Total Reflectance - Fourier Transform Infrared Spectroscopy.