Research

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Cold plasma

Cold atmospheric plasma, a lightning-like state generated from air or other gases with a high voltage.
PlasmaLeap Pin reactor treating cashew nuts

Plasma contains many active species and radicals that have antimicrobial activity, including reactive oxygen and nitrogen species (RONS).

Recent studies have shown the potential for cold plasma to be used for biofilm elimination without causing the bacteria to develop significant resistance. However, the precise mode of action is still the subject of debate.

Biofilms

Proposed mechanism of interaction of PAW with biofilms relying on active species to disrupt the matrix leading to effective biofilm dispersal. Under non-plasma conditions, an oxygen gradient will form in a microcolony (a). Interaction of PAW with microbial biofilms will generate a range of active RONS that can penetrate into the interior of microcolonies and kill biofilm cells. RONS will also lead to the disruption of the biofilm matrix and thus releasing cells from the biofilm interior (b)

Biofilms are complex communities of microbial cells (bacteria, archaea, and fungi) that are attached to a living or non-living surface and are encased within self-produced extracellular polymeric substances (EPS).

Biofilms have several characteristics that ensure their survival in a range of adverse environmental conditions, including high cell numbers, close cell proximity to allow easy genetic exchange (e. g. for resistance genes), cell communication, and protection through the production of an exopolysaccharide matrix. Together, these characteristics make it difficult to kill undesirable biofilms, despite the many studies aimed at improving the removal of biofilms. An elimination method that is safe, easy to deliver in physically complex environments, and not prone to microbial resistance is highly desired.

Plasma-activated water (PAW) and biofilms

Much of our research uses plasma that is generated in liquid, which is called plasma-activated water (PAW). We are interested in its interactions with biofilm components. Of particular interest is the diffusion of reactive species into biofilms, the formation of gradients, and the resulting interaction with the biofilm matrix and specific biofilm components. Such an understanding will provide significant benefits for tackling the ubiquitous problem of biofilm contamination in food, water, and medical areas. We are currently looking at E. coli and Staphylococcus biofilms. For an overview of the topic, please refer to our review paper: https://www.nature.com/articles/s41522-020-00180-6 This project is funded by an ARC discovery grant.

Plasma-activated water (PAW) and fungi

PAW is investigated for its activity against fungi. This project is done in collaboration with Prof. Dee Carter. It investigates the possible use of PAW towards the newly emerged fungal pathogen Candida auris.

Cold plasma virus interactions

In collaboration with A/Prof. Tim Newsome a recent Honours student (Matt Walker) investigated the effect of PAW against the highly resilient Ectromelia virus (ECTV).

Matt Walker presenting his final Honours talk.

PAW as a sanitizer for fresh produce washing

4 Ph.D. students from the ARC training center for Food Safety in the Fresh Produce Industry completed an internship project comparing the effectiveness of PAW to other sanitizers.

Ph.D. student Joanna Rothwell washing fresh produce
Cold plasma treatment of cotton seeds
Plasma treatment (left) of cotton seeds that are inoculated with fungi sterilizes and enhances germination compared to untreated control (right)

Gas plasma can be used to treat agricultural seeds to improve germination and enhance plant growth. This project was done at CSIRO Manufacturing and investigated the effect of gas plasma on cotton seeds. Results were published here: https://www.nature.com/articles/s41598-018-32692-9

Another project with the University of Sydney Institute for Agriculture (SIA) looks to unravel the mechanisms behind the use of cold plasma for seed germination improvements.