Efficacy of Different Carrier Gases for Barrier Discharge Plasma Generation Compared to Chlorhexidine on the Survival of Pseudomonas aeruginosa Embedded in Biofilm in vitro

Because of its antimicrobial properties, nonthermal plasma could serve as an alternative to chemical antisepsis in wound treatment. Therefore, this study investigated the inactivation of biofilm-embedded Pseudomonas aeruginosa SG81 by a surface barrier-discharged (SBD) plasma for 30, 60, 150 and 300 s. In order to optimize the efficacy of the plasma, different carrier gases (argon, argon admixed with 1% oxygen, and argon with increased humidity up to approx. 80%) were tested and compared against 0.1% chlorhexidine digluconate (CHG) exposure for 600 s. The antimicrobial efficacy was determined by calculating the difference between the numbers of colony-forming units (CFU) of treated and untreated biofilms. Living bacteria were distinguished from dead by fluorescent staining and confocal laser scanning microscopy. Both SBD plasmas and CHG showed significant antimicrobial effects compared to the untreated control. However, plasma treatment led to a higher antimicrobial reduction (argon plasma 4.9 log10 CFU/cm2, argon with admixed oxygen 3 log10 CFU/cm2, and with increased gas humidity 2.7 log10 CFU/cm2 after 300 s) compared to CHG. In conclusion, SBD plasma is suitable as an alternative to CHG for inactivation of Pseudomonas aeruginosa embedded in biofilm. Further development of SBD plasma sources and research on the role of carrier gases and humidity may allow their clinical application for wound management in the future

Skin Disinfection by Plasma-Tissue Interaction: Comparison of the Effectivity of Tissue-Tolerable Plasma and a Standard Antiseptic

Wound healing disorders frequently occur due to biofilm formation on wound surfaces requiring conscientious wound hygiene. Often, the application of conventional liquid antiseptics is not sufficient and sustainable as (1) the borders and the surrounding of chronic wounds frequently consist of sclerotic skin, impeding an effectual penetration of these products, and (2) the hair follicles representing the reservoir for bacterial recolonization of skin surfaces are not affected. Recently, it has been reported that tissue-tolerable plasma (TTP), which is used at a temperature range between 35 and 45°C, likewise has disinfecting properties. In the present study, the effectivity of TTP and a standard liquid antiseptic was compared in vitro on porcine skin. The results revealed that TTP was able to reduce the bacterial load by 94%, although the application of the liquid antiseptic remained superior as it reduced the bacteria by almost 99%. For in vivo application, however, TTP offers several advantages. On the one hand, TTP enables the treatment of sclerotic skin as well, and on the other hand, a sustainable disinfection can be realized as, obviously, also the follicular reservoir is affected by TTP

Treatment of Candida albicans biofilms with low-temperature plasma induced by dielectric barrier discharge and atmospheric pressure plasma jet

Because of some disadvantages of chemical disinfection in dental practice (especially denture cleaning), we investigated the effects of physical methods on Candida albicans biofilms. For this purpose, the antifungal efficacy of three different low-temperature plasma devices (an atmospheric pressure plasma jet and two different dielectric barrier discharges (DBDs)) on Candida albicans biofilms grown on titanium discs in vitro was investigated. As positive treatment controls, we used 0.1% Chlorhexidine digluconate (CHX) and 0.6% sodium hypochlorite (NaOCl). The corresponding gas streams without plasma ignition served as negative treatment controls. The efficacy of the plasma treatment was determined evaluating the number of colony-forming units (CFU) recovered from titanium discs. The plasma treatment reduced the CFU significantly compared to chemical disinfectants. While 10 min CHX or NaOCl exposure led to a CFU log 10 reduction factor of 1.5, the log10 reduction factor of DBD plasma was up to 5. In conclusion, the use of low-temperature plasma is a promising physical alternative to chemical antiseptics for dental practice. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Ionization by bulk heating of electrons in capacitive radio frequency atmospheric pressure microplasmas

Electron heating and ionization dynamics in capacitively coupled radio frequency (RF) atmospheric pressure microplasmas operated in helium are investigated by Particle in Cell simulations and semi-analytical modeling. A strong heating of electrons and ionization in the plasma bulk due to high bulk electric fields are observed at distinct times within the RF period. Based on the model the electric field is identified to be a drift field caused by a low electrical conductivity due to the high electron-neutral collision frequency at atmospheric pressure. Thus, the ionization is mainly caused by ohmic heating in this "Omega-mode". The phase of strongest bulk electric field and ionization is affected by the driving voltage amplitude. At high amplitudes, the plasma density is high, so that the sheath impedance is comparable to the bulk resistance. Thus, voltage and current are about 45{\deg} out of phase and maximum ionization is observed during sheath expansion with local maxima at the sheath edges. At low driving voltages, the plasma density is low and the discharge becomes more resistive resulting in a smaller phase shift of about 4{\deg}. Thus, maximum ionization occurs later within the RF period with a maximum in the discharge center. Significant analogies to electronegative low pressure macroscopic discharges operated in the Drift-Ambipolar mode are found, where similar mechanisms induced by a high electronegativity instead of a high collision frequency have been identified

Polypragmasie in der Behandlung infizierter Wunden - Schlussfolgerungen aus der Perspektive der Niedertemperaturplasma-Technologie für die Plasma-Wundbehandlung

As long as a wound is infected, the healing process cannot begin. The indication for wound antiseptic is dependent on the interaction between the wound, the causative micro-organisms, and the host immune system. An uncritical colonisation is a condition whereby micro-organisms on a wound will proliferate, yet the immune system will not react excessively. Wound antiseptic is most often not necessary unless for epidemiologic reasons like colonisation with multi-resistant organisms. In most instances of a microbial contamination of the wound and colonisation, thorough cleaning will be sufficient. Bacterial counts above 105 to 106 cfu per gram tissue (critical colonisation) might decrease wound healing due to release of toxins, particularly in chronic wounds. Traumatic and heavily contaminated wounds therefore will require anti-infective measures, in particular wound antiseptic. In such situations, even a single application of an antiseptic compound will significantly reduce the number of pathogens, and hence, the risk of infection. If a wound infection is clinically manifest, local antiseptics and systemic antibiotics are therapeutically indicated. The prophylactic and therapeutic techniques for treatment of acute and chronic wounds (chemical antiseptics using xenobiotics or antibiotics, biological antiseptic applying maggots, medical honey or chitosan, physical antiseptic using water-filtered infrared A, UV, or electric current) mostly have been empirically developed without establishing a fundamental working hypothesis for their effectiveness. The most important aspect in controlling a wound infection and achieving healing of a wound is meticulous debridement of necrotic material. This is achieved by surgical, enzymatic or biological means e.g. using maggots. However, none of these methods (with some exception for maggots) is totally gentle to vital tissue and particularly chemical methods possess cytotoxicity effects. Derived from the general principles of antiseptic wound treatment, the following working hypothesis is postulated: the most ideal constellation for treatment of wounds is the superficial destruction of microbial layers without deep tissue alteration, like it is caused by antiseptics, in order not to endanger the regenerative granulation tissue. At the same time, it is desirable to support and increase cell proliferation and granulation capacities. These two aspects might be achieved by using low temperature plasma technology.Solange eine Wunde infiziert ist, kommt der Heilungsprozess nicht zum Abschluss. Die Indikation zur Wundantiseptik ist abhängig von der Wechselwirkung Wunde - Mikroorganismus - Wirt: Bei mikrobieller Kontamination bzw. Kolonisation ist die wirksame Reinigung der Wunde ausreichend. Bei größeren traumatischen kontaminierten Wunden kann durch einmalige präventive Antiseptik eine Reduzierung postoperativer Infektionen erreicht werden. Bei unkritischer Kolonisation handelt es sich um die Vermehrung von auf die Wunde gelangten Erregern ohne klinische Wirtsreaktion. Auch hier ist keine Antiseptik erforderlich, außer aus epidemiologischer Indikation (multiresistente Erreger). Bakterienzahlen in der Wunde >105-106 KBE/g hemmen die Wundheilung durch Toxinfreisetzung (kritische Kolonisation) speziell bei chronischen Wunden bis zum Stillstand der Heilung. Hier ist eine "milde Antiseptik" mit gleichzeitiger Endotoxinabsorption oder -inaktivierung indiziert. Bei klinisch manifester Infektion mit lokaler und/oder systemischer Wirtsreaktion (Sepsis) ist die therapeutische Anwendung von Antiseptika indiziert, andernfalls kommt zur Defektheilung und im ungünstigen Fall zur Sepsis. Die Verfahren zur antiseptischen Behandlung akuter und chronischer Wunden (chemische Antiseptik mit Xenobiotika oder Antibiotika, biologische Antiseptik mit Maden, Bienenhonig oder Chitosan, physikalische Antiseptik mit wIRA, UV, Elektrostimulation) wurden empirisch ohne Zugrundelegung einer übergeordneten Arbeitshypothese eingeführt. Voraussetzung für die Wundheilung und Beherrschung einer Wundinfektion ist das effektive Debridement. Dieses erfolgt chirurgisch, enzymatisch oder mittels Maden. Zur Erregerinaktivierung werden chemische oder biologische Antiseptika sowie physikalische Verfahren eingesetzt. Diesen Verfahren gemeinsam ist eine mehr oder weniger ausgeprägte Zytotoxizität. Aus der Verallgemeinerung der Wirkprinzipien zur antiseptischen Wundbehandlung wird folgende Arbeitshypothese abgeleitet: Die ideale Konstellation zur Wundbehandlung ist die oberflächliche Zerstörung des mikrobiellen Biofilms auf der Wunde ohne antiseptische Tiefenwirkung, um das sich regenerierende Gewebe nicht zu hemmen. Gleichzeitig soll durch das Behandlungsprinzip die Wundheilung (Zellproliferation, Granulozytenleistung) im sich regenerierenden Gewebe stimuliert werden. Niedertemperaturplasma soll so konfiguriert werden, dass es die Anforderungen der Arbeitshypothese erfüllt

Plasma-oxidative degradation of polyphenolics – Influence of non-thermal gas discharges with respect to fresh produce processing

Non-thermal plasma treatment is a promising technology to enhance the shelf-life of fresh or minimaly processed food. An efficient inactivation of microorganisms comes along with a moderate heating of the treated surface. To elucidate the influence of highly reactive plasma-immanent species on the stability and chemical behaviour of phytochemicals, several polyphenolics were exposed to an atmospheric pressure plasma jet (APPJ). The selected flavonoids are ideal target compounds due to their antioxidant activity protecting cells against the damaging effects of reactive oxygen species such as singlet oxygen, superoxide, peroxyl radicals, hydroxyl radicals and peroxynitrite. Reactions were carried out at various radio-frequency voltages, using Ar as a feeding gas. Degradation was followed by reversed-phase high-performance liquid chromatography