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Open AccessArticle

Characterization of Antimicrobial Effects of Plasma-Treated Water (PTW) Produced by Microwave-Induced Plasma (MidiPLexc) on Pseudomonas fluorescens Biofilms

1
Leibniz Institute for Plasma Science and Technology (INP), Felix-Hausdorff-Str. 2, 17489 Greifswald, Germany
2
Institute of Microbiology, University of Greifswald Felix-Hausdorff-Str. 8, 17489 Greifswald, Germany
3
School of Food Science and Environmental Health, College of Sciences and Health, Technological University, Dublin, Cathal Brugha Street, D01 HV58 Dublin, Ireland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2020, 10(9), 3118; https://doi.org/10.3390/app10093118
Received: 7 April 2020 / Revised: 21 April 2020 / Accepted: 28 April 2020 / Published: 29 April 2020
(This article belongs to the Special Issue Application of Plasma Technology in Bioscience and Biomedicine)
For the decontamination of surfaces in the food production industry, plasma-generated compounds such as plasma-treated water or plasma-processed air offer many promising possibilities for future applications. Therefore, the antimicrobial effect of water treated with microwave-induced plasma (MidiPLexc) on Pseudomonas fluorescens biofilms was investigated. A total of 10 mL deionized water was treated with the MidiPLexc plasma source for 100, 300 and 900 s (pretreatment time) and the bacterial biofilms were exposed to the plasma-treated water for 1, 3 and 5 min (post-treatment time). To investigate the influence of plasma-treated water on P. fluorescens biofilms, microbiological assays (colony-forming units, fluorescence and XTT assay) and imaging techniques (fluorescence microscopy, confocal laser scanning microscopy, and atomic force microscopy) were used. The colony-forming units showed a maximum reduction of 6 log10 by using 300 s pretreated plasma water for 5 min. Additionally, a maximum reduction of 81% for the viability of the cells and a 92% reduction in the metabolic activity of the cells were achieved by using 900 s pretreated plasma water for 5 min. The microscopic images showed evident microbial inactivation within the biofilm even at the shortest pretreatment (100 s) and post-treatment (1 min) times. Moreover, reduction of the biofilm thickness and increased cluster formation within the biofilm was detected. Morphologically, the fusion of cell walls into a uniform dense cell mass was detectable. The findings correlated with a decrease in the pH value of the plasma-treated water, which forms the basis for the chemically active components of plasma-treated water and its antimicrobial effects. These results provide valuable insights into the mechanisms of inactivation of biofilms by plasma-generated compounds such as plasma-treated water and thus allow for further parameter adjustment for applications in food industry. View Full-Text
Keywords: biofilm degradation; decontamination; inactivation; food spoilage; cluster formation biofilm degradation; decontamination; inactivation; food spoilage; cluster formation
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Handorf, O.; Pauker, V.I.; Schnabel, U.; Weihe, T.; Freund, E.; Bekeschus, S.; Riedel, K.; Ehlbeck, J. Characterization of Antimicrobial Effects of Plasma-Treated Water (PTW) Produced by Microwave-Induced Plasma (MidiPLexc) on Pseudomonas fluorescens Biofilms. Appl. Sci. 2020, 10, 3118.

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