Oxidative modification and electrochemical inactivation of Escherichia coli upon cold atmospheric pressure plasma exposure

Marlène Dezest,Mickael Le Bechec,Laurent Chavatte,Sarah Cousty,Anne Nègre-Salvayre,Franck Clément,Damien Quinton,Anne-Laure Bulteau,Jean Pierre Cambus,Stéphane Arbault

doi:10.1371/journal.pone.0173618

Abstract

Cold atmospheric pressure plasmas (CAPPs) are known to have bactericidal effects but the mechanism of their interaction with microorganisms remains poorly understood. In this study the bacteria Escherichia coli were used as a model and were exposed to CAPPs. Different gas compositions, helium with or without adjunctions of nitrogen or oxygen, were used. Our results indicated that CAPP induced bacterial death at decontamination levels depend on the duration, post-treatment storage and the gas mixture composition used for the treatment. The plasma containing O2 in the feeding gas was the most aggressive and showed faster bactericidal effects. Structural modifications of treated bacteria were observed, especially significant was membrane leakage and morphological changes. Oxidative stress caused by plasma treatment led to significant damage of E. coli. Biochemical analyses of bacterial macromolecules indicated massive intracellular protein oxidation. However, reactive oxygen and nitrogen species (RONS) are not the only actors involved in E. coli’s death, electrical field and charged particles could play a significant role especially for He-O2 CAPP.

Highlights

Cold Atmospheric Pressure Plasmas (CAPPs) are partially ionized gases generated at near ambient temperature and pressure
The aim of this study was to focus on the interactions between active species produced by 3 different types of plasma: He, He/O2 and He/N2, and the bacteria E. coli and begin to assess how the chemistry involved in the liquid and the electrical field associated with the guided ionization wave or generated in the environment of the CAPP or at the bacterial membrane may lead to bacteria inactivation
Our results provide support for the hypothesis that upon treatment with He and He-N2, free radicals generated in the phosphate buffered saline (PBS) mediate bacterial inactivation thereby altering protein homeostasis and membrane integrity

Summary

Introduction

Cold Atmospheric Pressure Plasmas (CAPPs) are partially ionized gases generated at near ambient temperature and pressure. Depending on specific experimental conditions, a nonequilibrium state is achieved which keeps the plasma close to room temperature with production of a reactive mix containing electrons, positive and negative ions, groups of reactive species such as reactive oxygen (ROS) or nitrogen (RNS) species, neutral species in fundamental and excited states (metastables and radiative states) and highly energetic photons [1,2,3]. CAPP and oxidative and electrochemical damages to Escherichia coli funders had no role in the study design, data collection and analysis, decision to publish or preparation of the manuscript

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