Veronika Medvecká

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.

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.