Abstract
Low-temperature plasmas (LTPs) have a proven bactericidal activity governed by the generated reactive oxygen and nitrogen species (RONS) that target microbial cell components. However, RONS also interact with biomolecules in the environment. Here we assess the impact of these interactions upon exposure of liquid suspensions with variable organic content to an atmospheric-pressure dielectric barrier discharge plasma jet. Salmonella enterica serovar Typhimurium viability in the suspension was reduced in the absence [e.g., phosphate buffered saline (PBS)], but not in the presence of (high) organic content [Dulbecco's Modified Eagle's Medium (DMEM), DMEM supplemented with foetal calf serum, and Lysogeny Broth]. The reduced viability of LTP-treated bacteria in PBS correlated to a loss of membrane integrity, whereas double-strand DNA breaks could not be detected in treated single cells. The lack of bactericidal activity in solutions with high organic content correlated with a relative decrease of •OH and O3/O2(a1n}{}{Delta }text{g}n)/O, and an increase of H2O2 and n}{}mathrm{NO}_{2}^{-}n in the plasma-treated solutions. These results indicate that the redox reactions of LTP-generated RONS with nontarget biomolecules resulted in a RONS composition with reduced bactericidal activity. Therefore, the chemical composition of the bacterial environment should be considered in the development of LTP for antimicrobial treatment, and may affect other biomedical applications as well.
Highlights
T HE ANTIMICROBIAL activity of low-temperature plasmas (LTPs) has attracted significant interest in the biomedical field for its possible applications for wound decontamination [1], [2]
We observed a 3.5-log reduction in viable bacteria exposed to LTP in phosphate buffered saline (PBS) (99.9%–99.99% inactivation) and 1.5-log reduction in H2O (90%–99% inactivation) (P < 0.0001; Fig. 2)
The complex interactions between reactive oxygen and nitrogen species (RONS) delivered by LTP and organic molecules in biological systems generate additional reactive species and potentially cytotoxic by-products
Summary
T HE ANTIMICROBIAL activity of low-temperature plasmas (LTPs) has attracted significant interest in the biomedical field for its possible applications for wound decontamination [1], [2]. The partially ionized gas is an important source of reactive oxygen and nitrogen species (RONS) [2], known to cause oxidative damage to the structure and function of biomolecules in cells [3]–[5] These redox reactions are not restricted to RONS and biomolecules in target cells, as the unspecific action of RONS enables their reaction with biomolecules present in the bacterial environment. LTP treatment leads to damage or changes in a range of biomolecules that each could cause or contribute to the bactericidal activity, including membrane damage and DNA strand breakage [10], [11] This damage has been documented in situ, i.e., in live bacterial cells [12], as well as for purified components [13]. Biomolecules can alter the physiological state of the bacteria that may facilitate resistance to LTP-induced damage
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