Abstract
Cold plasma generated in air at atmospheric pressure is an extremely effective antimicrobial agent, with proven efficacy against clinically relevant bacterial biofilms. The specific mode of bacterial inactivation is highly dependent upon the configuration of the plasma source used. In this study, the mode of microbial inactivation of a surface barrier discharge was investigated against Escherichia coli biofilms grown on polypropylene coupons. Different modes of exposure were considered and it was demonstrated that the long-lived reactive species created by the plasma are not solely responsible for the observed microbial inactivation. It was observed that a synergistic interaction occurs between the plasma generated long-lived reactive species and ultraviolet (UV) photons, acting to increase the antimicrobial efficacy of the approach by an order of magnitude. It is suggested that plasma generated UV is an important component for microbial inactivation when using a surface barrier discharge; however, it is not through the conventional pathway of direct DNA damage, rather through the synergistic interaction between liquid in the biofilm matrix and long-lived chemical species created by the discharge.
Highlights
Plasma—regarded as the fourth state of matter—is a partially or completely ionised gas with unique chemical and physical properties which generates a wide range of highly reactive chemical agents when created in the ambient air
Our results demonstrate that effective microbial inactivation is significantly enhanced through the synergistic interaction between Cold Atmospheric Plasma (CAP) generated UV photons and long-lived Reactive Oxygen and Nitrogen Species (RONS) when they interact with the extracellular polymeric substance (EPS) matrix of the biofilm
The distribution of plasma generated species as a function of distance from the plasma generating electrode is shown in Fig 2B and 2C, a clear difference in the gas phase RONS composition can be observed depending on distance from the plasma generating electrode
Summary
Plasma—regarded as the fourth state of matter—is a partially or completely ionised gas with unique chemical and physical properties which generates a wide range of highly reactive chemical agents when created in the ambient air. It has been increasingly studied due its antimicrobial, blood coagulation, wound healing and anti-tumour capability as well as in dentistry and several other biomedical applications [1,2,3,4,5]. CAP is operated at near-room temperature and generates predominantly Reactive Oxygen and Nitrogen Species (RONS), electrons, ions and UV radiation. The specific chemical composition of CAP strongly depends on its generation parameters such as power input, frequency, voltage, working gas flow and/or composition [7].
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