A compact pulse-modulation air plasma jet for the inactivation of chronic wound bacteria: Bactericidal effects & host safety

Previously, a novel compact low-temperature plasma jet device with adjustable pulse-parameters was developed to use ambient air as a plasma source for the inactivation of chronic wound bacteria. Its adjustable burst-mode pulse was proved to be highly beneficial for the controllable generation of the desired reactive oxygen and nitrogen species. In this study, further bactericidal effects and its safety on human dermal fibroblasts (HDF) were investigated. The generated plasma inactivated Pseudomonas aeruginosa (PA) and Staphylococcus aureus (SA) effectively in a time- and dose-dependent manner. Quantification of colony-forming units from bacterial biofilms confirmed the elimination of biofilms formed by PA or SA. Next, HDF cells were plasma-treated and the morphology was observed using an inverted microscope and a scanning electron microscope. No particular morphological changes were observed on cell membrane and cell attachment. MTT assay of the HDF cells after plasma exposure also confirmed the functional enzymatic activity of the cells up to 5 min of treatment. Flow cytometric assay for annexin V and 7-AAD showed that plasma exposure did not significantly induce apoptosis or necrosis of the cell. Intracellular nitric oxide, reactive oxygen species, and Ki-67 protein, a marker for cell proliferation, were also measured by flow cytometry. Intracellular levels of nitric oxide significantly increased, while reactive oxygen species and Ki-67 protein showed no significant alteration after the plasma exposure. Taken together, we demonstrated that the newly developed adjustable-pulse low-temperature air plasma jet device was an effective tool for the elimination of bacteria especially on chronic wound, where the treatment is needed to be least invasive and safe for the surrounding tissue.