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Neutrophil extracellular trap formation is elicited in response to cold physical plasma
Cold physical plasma is an ionized gas with a multitude of components, including hydrogen peroxide and other reactive oxygen and nitrogen species. Recent studies suggest that exposure of wounds to cold plasma may accelerate healing. Upon wounding, neutrophils are the first line of defense against invading microorganisms but have also been identified to play a role in delayed healing. In this study, we examined how plasma treatment affects the functions of peripheral blood neutrophils. Plasma treatment induced oxidative stress, as assessed by the oxidation of intracellular fluorescent redox probes; reduced metabolic activity; but did not induce early apoptosis. Neutrophil oxidative burst was only modestly affected after plasma treatment, and the killing of Pseudomonas aeruginosa and Staphylococcus aureus was not significantly affected. Intriguingly, we found that plasma induced profound extracellular trap formation. This was inhibited by the presence of catalase during plasma treatment but was not replicated by adding an equivalent concentration of hydrogen peroxide. Plasma-induced neutrophil extracellular trap formation was not dependent on the activity of myeloperoxidase or NADPH oxidase 2 but seemed to involve short-lived molecules. The amount of DNA release and the time course after plasma treatment were similar to that with the common neutrophil extracellular trap inducer PMA. After neutrophil extracellular traps had formed, concentrations of IL-8 were also significantly increased in supernatants of plasma-treated neutrophils. Both neutrophil extracellular traps and IL-8 release may aid antimicrobial activity and spur inflammation at the wound site. Whether this aids or exacerbates wound healing needs to be tested.
Antimicrobial effects of microwave-induced plasma torch (MiniMIP) treatment on Candida albicans biofilms
The susceptibility of Candida albicans biofilms to a non-thermal plasma treatment has been investigated in terms of growth, survival and cell viability by a series of in vitro experiments. For different time periods, the C. albicans strain SC5314 was treated with a microwave-induced plasma torch (MiniMIP). The MiniMIP treatment had a strong effect (reduction factor (RF) = 2.97 after 50 s treatment) at a distance of 3 cm between the nozzle and the superior regions of the biofilms. In addition, a viability reduction of 77% after a 20 s plasma treatment and a metabolism reduction of 90% after a 40 s plasma treatment time were observed for C. albicans. After such a treatment, the biofilms revealed an altered morphology of their cells by atomic force microscopy (AFM). Additionally, fluorescence microscopy and confocal laser scanning microscopy (CLSM) analyses of plasma-treated biofilms showed that an inactivation of cells mainly appeared on the bottom side of the biofilms. Thus, the plasma inactivation of the overgrown surface reveals a new possibility to combat biofilms. © 2019 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.