Cold DC-Operated Air Plasma Jet for the Inactivation of Infectious Microorganisms

Abstract

We evaluated a nonthermal plasma jet for a respective use to prevent infections from bacteria and yeasts. The plasma jet is generated from the flow of ambient air with 8 slm through a microhollow cathode discharge assembly that is operated with a direct current of 30 mA. With these parameters, the temperature in the jet reaches 43 • C at 10 mm from the discharge. Agar plates that were inoculated with Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, and Candida kefyr were treated at this distance, moving the plates through the jet in a meander that covered a 2 cm by 2 cm area. Different exposure times were realized by changing the speed of the movement and adjusting the distance between consecutive passes. S. aureus was most responsive to the exposure with a reduction in the number of colony forming units of 5.5 log steps in 40 s. All other microorganisms show a more gradual inactivation with exposure times. For all bacteria, a clearing of the treated area is achieved in about 2.5-3.5 min, corresponding to log-reduction factors of 5.5-6.5. Complete inactivation of the yeast requires about 7 min. Both S. aureus and C. kefyr show considerable inactivation also outside the immediate treatment area, while P. aeruginosa and A. baumannii do not. We conclude that differences in the morphologies of the membrane structures are responsible for the diverging results, together with a targeted response to different agents provided with the plasma jet. For the gram negative bacteria, we hold short-lived agents, acting across a short range, responsible, while for the other microorganisms, longer lived species seem more important. Our measurements show that neither heat, ultraviolet radiation, nor the generation of ozone can be responsible for the observed results. The most prominent long lived reaction product found is nitric oxide, which, by itself or through induced chemical reactions, might affect cell viability.

Membrane damage and active but nonculturable state in liquid cultures of Escherichia coli treated with an atmospheric pressure plasma jet

“…The strength of this technology is its ability to provide "cold" plasmas at atmospheric pressure, such that the temperatures are close to room temperature and are not harmful to plastic materials or skin. A variety of different plasma sources have been developed for biomedical applications [1], the majority of which are based on either dielectric barrier-type discharge (DBD) or plasma jets [8][9][10][11][12]. In addition to these two methods, a variety of other approaches are being pursued, including corona and arc discharges [13][14][15][16][17].…”

DC Operated Air Plasma Jet for Antimicrobial Copper Coatings on Temperature Labile Surfaces

“…So far no noticeable differences that are dependent on the electrode material have been observed in our inactivation studies [3]. Conversely, we have deliberately used copper electrodes to investigate potential copper coatings.…”

“…The jet was originally developed and investigated for the treatment of body tissue, for example, skin, and is based on a microhollow cathode discharge geometry [3]. A metal tube with an inner diameter of 0.8 mm is separated from a grounded electrode that is likewise perforated with a 0.8-mm diameter hole and aligned with the tube.…”

A reference protocol for comparing the biocidal properties of gas plasma generating devices

“…For a plasma jet with an effective area of a few mm 2 , for example, use of membranes of dimensions as specified here would be appropriate if the jet were mounted on a 2D moving stage to ensure even plasma treatment across the membrane [35]. Alternatively, the procedures described here could be applied to membranes of smaller diameter.…”