Award Presentation Australian Society for Microbiology Annual Scientific Meeting 2022

The Antibacterial Power of Plasma-Activated Water (82372)

Joanna G Rothwell 1 , David Alam 2 , Binbin Xia 2 , Behdad Soltani 2 , Robyn McConchie 1 , Renwu Zhou 2 , Patrick Cullen 2 , Anne Mai-Prochnow 2 , Dee A Carter 1 3
  1. ARC Training Centre for Food Safety in the Fresh Produce Industry, School of Life and Environmental Sciences, Faculty of Science, The University of Sydney, Sydney, NSW, Australia
  2. School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, NSW, Australia
  3. The Marie Bashir Institute for Infectious Diseases and Biosecurity, University of Sydney, SYDNEY, New South Wales, Australia

Fresh foods can be contaminated with pathogenic microbes which can lead to foodborne disease outbreaks. To reduce this risk, fresh fruit and vegetables are processed with a sanitiser wash to increase shelf life and safety. Existing sanitisers are expensive, susceptible to failure or have negative environmental impacts. Therefore the development of effective and commercially viable sanitisers is required.

Plasma is the fourth state of matter of a given material. Plasma activated water (PAW) is produced from plasma-water interactions and contains a cocktail of reactive species and free radicals. PAW has demonstrated efficacy as a sanitiser in multiple applications, however there is a need for further optimisation.

The aim of this study was to compare two  plasma reactors for their antimicrobial efficacy against foodborne disease organisms. The reactors were a bubble spark discharge (BSD) reactor and a dielectric barrier discharge-diffuser (DBDD) reactor (Figure 1). The experiments were performed at atmospheric conditions using air as the processing gas and Milli-Q and tap water as PAW substrates.

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FIGURE 1: Schematic of the BSD (a) and DBDD reactor (b) for PAW production1

Model organisms Listeria innocua and Escherichia coli were added to BSD and DBBD-PAW systems and tested in situ across 3 discharge frequencies. Pathogenic bacteria Listeria monocytogenes, E. coli and Salmonella enterica were subsequently tested at the optimal conditions. DBDD-PAW reduced 6-log of bacteria in less than 1 min in all conditions. The BSD-PAW resulted in a high bacterial reduction but was less effective overall.

The physicochemical properties of the generated PAW were assessed, and scavenger assays were used to sequester individual reactive species. The addition of tiron, a scavenger of superoxide, quenched the antibacterial activity of the DBDD-PAW, demonstrating that superoxide ions and/or downstream reactions were primarily responsible for the observed antimicrobial activity.

This research demonstrates the potential of DBDD-PAW produced using tap water and air as a feasible and inexpensive option for broad antimicrobial applications including the decontamination of fresh foods.

  1. Rothwell JG, Alam D, Carter DA, Soltani B, McConchie R, Zhou RW, Cullen PJ, Mai-Prochnow A. 2022. The antimicrobial efficacy of plasma-activated water against listeria and e. Coli is modulated by reactor design and water composition. Journal of Applied Microbiology. 132(4):2490-2500.