Abstract
In continuation of our previous reports on the broad-spectrum antimicrobial activity of atmospheric non-thermal dielectric barrier discharge (DBD) plasma treated N-Acetylcysteine (NAC) solution against planktonic and biofilm forms of different multidrug resistant microorganisms, we present here the chemical changes that mediate inactivation of Escherichia coli. In this study, the mechanism and products of the chemical reactions in plasma-treated NAC solution are shown. UV-visible spectrometry, FT-IR, NMR, and colorimetric assays were utilized for chemical characterization of plasma treated NAC solution. The characterization results were correlated with the antimicrobial assays using determined chemical species in solution in order to confirm the major species that are responsible for antimicrobial inactivation. Our results have revealed that plasma treatment of NAC solution creates predominantly reactive nitrogen species versus reactive oxygen species, and the generated peroxynitrite is responsible for significant bacterial inactivation.
Highlights
In the spectrum of 1-minute plasma treated NAC solution, a specific peak appears at 332 nm, which belongs to S-nitroso-N-acetyl cysteine (SNAC) that is a type of S-nitrosothiol
In the spectrum of 2-minute plasma treated NAC solution a new peak starts to appear at 302 nm and the absorbance value of this peak increases after 3 minutes of plasma treatment (Fig. 2A)
The findings suggest that plasma treatment turns NAC solution into an acidic mixture of ROS and RNS where both contribute to bacterial inactivation
Summary
Our group has reported that N-Acetylcysteine (NAC) solution gains antimicrobial effect when treated with non-thermal, atmospheric dielectric barrier discharge (DBD) plasma (operated in ambient air, without using technical gases). We hypothesized that plasma treatments of NAC solution generate RNS and ROS and their interactions further give rise reactive product which in the presence of plasma-induced acidic pH gets stabilized and exhibit strong antimicrobial properties. In the present study the techniques such as nitrite and nitrate detection, UV-vis spectrum analysis, FT-IR analysis, NMR analysis, were performed in order to evaluate chemical modifications in NAC solution following non-thermal atmospheric DBD plasma treatment. The antimicrobial effect of this solution originates from diffused ROS and RNS in liquid as opposed to direct plasma treatment, where physical impacts such as UV, electrical field, and electron bombardment are major contributors to the biocidal effect
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