Mechanism of Inactivation by High Voltage Atmospheric Cold Plasma Differs between Escherichia coli and Staphylococcus aureus

Atmospheric cold plasma (ACP) is a promising non-thermal technology effective against a wide range of pathogenic microorganisms. Reactive oxygen species (ROS) play a crucial inactivation role when air or other oxygen containing gases are used. With strong oxidative stress, cells can be damaged by lipid peroxidation, enzyme inactivation and DNA cleavage. Identifying ROS and understanding their role is important to advance ACP applications to a range of complex microbiological issues. In this study, the inactivation efficacy of in-package, high voltage (80 kVRMS) ACP (HVACP) and the role of intracellular ROS were investigated. Two mechanisms of inactivation were observed where reactive species were found to either react primarily with the cell envelope or to damage intracellular components. E. coli was inactivated mainly by cell leakage and low level DNA damage. Conversely, S. aureus was mainly inactivated by intracellular damage with significantly higher levels of intracellular ROS observed and little envelope damage. However, for both bacteria studied, increasing treatment time had a positive effect on intracellular ROS levels generated