Synergistic antibacterial effects of low temperature plasma combined with pulsed electric fields

Low temperature plasmas and pulsed electric fields (PEF) can both be used as non-thermal disinfection methods. However, both approaches are based on different underlying interaction mechanisms with biological cells. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generally considered to be the most important agents for plasma-inactivation, and plasma induced oxidative stress is believed to cause cell damage and cell death accordingly¹. The most widely accepted explanation for inactivation by PEF-exposures is based on the accumulation of charges along the cell envelope and along internal membranes, eventually resulting in high transmembrane potentials and subsequent damage to membranes and cells². The different mechanisms suggest that a combination of both methods would provide a more effective decontamination than each approach by itself. In our study, we investigated combinations of low temperature plasma treatments with PEF-exposures for bacterial inactivation. Inactivation efficacy against Grampositive Staphylococcus aureus and Gram-negative Pseudomonas aerugionsa was determined by viability counts. Membrane integrity, membrane potential and intracellular ROS were studied by flow cytometry. Leakage of intracellular compounds, such as DNA and protein, was measured spectrophotometrically at 260 nm and 280 nm. The properties of the cell suspension, such as pH-value, conductivity, and RNS&ROS, were also investigated. Results show that combination treatments of low temperature plasma with PEF exhibited significant synergistic activities versus individual treatments for inactivation of bacteria.