Abstract
Non-thermal plasma at atmospheric pressure has been actively applied to sterilization. However, its efficiency for inactivating microorganisms often varies depending on microbial species and environments surrounding the microorganisms. We investigated the influence of environmental factors (surrounding media) on the efficiency of microbial inactivation by plasma using an eukaryotic model microbe, Saccharomyces cerevisiae, to elucidate the mechanisms for differential efficiency of sterilization by plasma. Yeast cells treated with plasma in water showed the most severe damage in viability and cell morphology as well as damage to membrane lipids, and genomic DNA. Cells in saline were less damaged compared to those in water, and those in YPD (Yeast extract, Peptone, Dextrose) were least impaired. HOG1 mitogen activated protein kinase was activated in cells exposed to plasma in water and saline. Inactivation of yeast cells in water and saline was due to the acidification of the solutions by plasma, but higher survival of yeast cells treated in saline may have resulted from the additional effect related to salt strength. Levels of hydroxyl radical (OH.) produced by plasma were the highest in water and the lowest in YPD. This may have resulted in differential inactivation of yeast cells in water, saline, and YPD by plasma. Taken together, our data suggest that the surrounding media (environment) can crucially affect the outcomes of yeast cell plasma treatment because plasma modulates vital properties of media, and the toxic nature of plasma can also be altered by the surrounding media.
Highlights
Reactive oxygen species (ROS) and reactive nitrogen species (RNS) have lethal effects on microorganisms [1]
Our study clearly demonstrates that non-thermal atmospheric pressure plasma generated different level of lethal effects on microorganisms through interaction with surrounding environments
A recent study demonstrated that the bactericidal effects of plasma in water and saline increase due to the acidification of solutions by air plasma and that phosphate buffered saline (PBS) exposed to N2 plasma becomes highly toxic to bacteria [18]
Summary
Reactive oxygen species (ROS) and reactive nitrogen species (RNS) have lethal effects on microorganisms [1]. Reactive species are a good means for attacking pathogenic microorganisms, and effective use of them provides a promising tool for controlling microbial diseases. As an alternative control tool, non-thermal plasma at atmospheric pressure developed in physics has been actively applied and examined for its effectiveness in microbial inactivation [5,6,7]. As a mixture of ionized gas, produces various ROS and RNS. These reactive species are thought to be the major components that have antimicrobial effects, but UV, ions, and the electric field from plasma are involved in killing microorganisms [8]
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