Bactericidal efficacy of tissue tolerable plasma on microrough titanium dental implants: An in-vitro-study

Surface decontamination remains challenging in peri-implant infection therapy. To investigate the bactericidal efficacy of tissue tolerable plasma, S. mitis biofilms were created in vitro on 32 microrough titanium dental implants. Biofilm imaging was performed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The implants were either rinsed with 1% NaCl as negative control (C) or irradiated with a diode laser (DL) for 60 sec as positive control or plasma (TTP60, TTP120) for 60 or 120 sec. Subsequently, colony forming units (CFU) were counted. Post-treatment, implants were further examined using fluorescence microscopy (FM). Median CFU counts differed significantly between TTP60, TTP120 and C (2.19 and 2.2 vs. 3.29 log CFU/ml; p = 0.012 and 0.024). No significant difference was found between TTP60 and TTP120 (p = 0.958). Logarithmic reduction factors were (TTP60) 2.21, (TTP120) 1.93 and (DL) 0.59. Prior to treatment, CLSM and SEM detected adhering bacteria. Post-treatment FM recorded that the number of dead cells was higher using TTP compared to DL and C. In view of TTP's effectiveness, regardless of resistance patterns and absence of surface alteration, its use in peri-implant infection therapy is promising. The results encourage conducting clinical studies to investigate its impact on relevant parameters.

Enhancement of Wound Healing by Non-Thermal N2/Ar Micro-Plasma Exposure in Mice with Fractional-CO2-Laser-Induced Wounds

Micro-plasma is a possible alternative treatment for wound management. The effect of micro-plasma on wound healing depends on its composition and temperature. The authors previously developed a capillary-tube-based micro-plasma system that can generate micro-plasma with a high nitric oxide-containing species composition and mild working temperature. Here, the efficacy of micro-plasma treatment on wound healing in a laser-induced skin wound mouse model was investigated. A partial thickness wound was created in the back skin of each mouse and then treated with micro-plasma. Non-invasive methods, namely wound closure kinetics, optical coherence tomography (OCT), and laser Doppler scanning, were used to measure the healing efficiency in the wound area. Neo-tissue growth and the expressions of matrix metallopeptidase-3 (MMP-3) and laminin in the wound area were assessed using histological and immunohistochemistry (IHC) analysis. The results show that micro-plasma treatment promoted wound healing. Micro-plasma treatment significantly reduced the wound bed region. The OCT images and histological analysis indicates more pronounced tissue regrowth in the wound bed region after micro-plasma treatment. The laser Doppler images shows that micro-plasma treatment promoted blood flow in the wound bed region. The IHC results show that the level of laminin increased in the wound bed region after micro-plasma treatment, whereas the level of MMP-3 decreased. Based on these results, micro-plasma has potential to be used to promote the healing of skin wounds clinically.

Effect of Atmospheric-Pressure Cold Plasma on Pathogenic Oral Biofilms and In Vitro Reconstituted Oral Epithelium

Considering the ability of atmospheric-pressure cold plasma (ACP) to disrupt the biofilm matrix and rupture cell structure, it can be an efficient tool against virulent oral biofilms. However, it is fundamental that ACP does not cause damage to oral tissue. So, this study evaluated (1) the antimicrobial effect of ACP on single- and dual-species biofilms of Candida albicans and Staphylococcus aureus as well as (2) the biological safety of ACP on in vitro reconstituted oral epithelium. Standardized cell suspensions of each microorganism were prepared for biofilm culture on acrylic resin discs at 37°C for 48 hours. The biofilms were submitted to ACP treatment at 10 mm of plasma tip-to-sample distance during 60 seconds. Positive controls were penicillin G and fluconazole for S. aureus and C. albicans, respectively. The biofilms were analyzed through counting of viable colonies, confocal laser scanning microscopy, scanning electron microscopy and fluorescence microscopy for detection of reactive oxygen species. The in vitro reconstituted oral epithelium was submitted to similar ACP treatment and analyzed through histology, cytotoxocity test (LDH release), viability test (MTT assay) and imunnohistochemistry (Ki67 expression). All plasma-treated biofilms presented significant log₁₀ CFU/mL reduction, alteration in microorganism/biofilm morphology, and reduced viability in comparison to negative and positive controls. In addition, fluorescence microscopy revealed presence of reactive oxygen species in all plasma-treated biofilms. Low cytotoxicity and high viability were observed in oral epithelium of negative control and plasma group. Histology showed neither sign of necrosis nor significant alteration in plasma-treated epithelium. Ki67-positive cells revealed maintenance of cell proliferation in plasma-treated epithelium. Atmospheric-pressure cold plasma is a promissing approach to eliminate single- and dual-species biofilms of C. albicans and S. aureus without having toxic effects in oral epithelium.

Antibacterial efficacy of a novel plasma reactor without an applied gas flow against methicillin resistant Staphylococcus aureus on diverse surfaces

The use of nonthermal plasma in the clinic has gained recent interest, as the need for alternative or supplementary strategies are necessary for preventing multi-drug resistant infections. The purpose of this study was to evaluate the antibacterial efficacy of a novel plasma reactor based on a high current version of sliding discharge and operated by nanosecond voltage pulses without an applied gas flow. This modification is advantageous for both portability and convenience. Bacterial inactivation was determined within a chamber by direct quantification of colony Jing units. Plasma exposure significantly inhibited the growth of Escherichia coli and Staphylococcus epidermidis following a 1-min application (p<0.001). S. epidermidis was more susceptible to the plasma after a 5-min exposure compared to E. coli. Temperature and pH measurements taken immediately before and after plasma exposure determined neither heat nor pH changes play a role in bacterial inactivation. Because of the notable effect on S. epidermidis, the effect of plasma exposure on several isolates and strains of the related opportunistic pathogen Staphylococcus aureus was quantified. While S. aureus isolates and strains were efficiently inactivated on an agar surface, subsequent testing on other clinically relevant surfaces demonstrated that the inactivation level, although significant, was reduced. This reduction appeared to depend on both the surface texture and the surface moisture content. These findings suggest this novel plasma source lacking an applied gas flow has potential application for surface bacterial decontamination.

Adjuvant antifungal therapy using tissue tolerable plasma on oral mucosa and removable dentures in oral candidiasis patients: a randomised double-blinded split-mouth pilot study

Extended use of antimycotics in oral candidiasis therapy gives rise to problems related to fungal drug resistance. The aim of this pilot study was to investigate the efficacy of tissue tolerable plasma (TTP) in denture stomatitis patients. It was hypothesised that (I): erythema and (IIa): complaint remission would be accelerated and (IIb): colony forming unit (CFU) reduction would be improved. The halves of the upper jaws of eight patients were randomly assigned to control (nystatin, chlorhexidine and placebo treatment) and test sides (nystatin, chlorhexidine and TTP administered six times each 7 days). The patients and the investigators, who were different from the therapists, were both blinded. Compared to the control sides, the erythema surface was reduced significantly more extensively on the test sides between 2 and 6 weeks of antifungal therapy (P ≤ 0.05). Visual analogue scale values and the frequency of moderate or heavy growth of Candida post-treatment did not differ significantly between both sides (P > 0.05). The primary hypothesis was confirmed, which may be interpreted as an accelerated remission. As drug therapy is usually limited to the time in which signs of infection are present, TTP might help reducing antifungal use. Even though the secondary hypotheses were not confirmed, persistence of Candida might be only colonisation.

Improvement of cutaneous microcirculation by cold atmospheric plasma (CAP): Results of a controlled, prospective cohort study

BACKGROUND

Cold atmospheric plasma (CAP) has proven its benefits in the reduction of various bacteria and fungi in both in vitro and in vivo studies. Moreover, CAP generated by dielectric barrier discharge (DBD) promoted wound healing in vivo. Charged particles, chemically reactive species (such as O3, OH, H2O2, O, NxOy), ultraviolet radiation (UV-A and UV-B), strong oscillating electric fields as well as weak electric currents are produced by DBD operated in air. However, wound healing is a complex process, depending on nutrient and oxygen supply via cutaneous blood circulation. Therefore, this study examined the effects of CAP on cutaneous microcirculation in a prospective cohort setting.

HYPOTHESIS

Cold atmospheric plasma application enhances cutaneous microcirculation.

METHODS

Microcirculatory data of 20 healthy subjects (11 males, 9 females; mean age 35.2 ± 13.8 years; BMI 24.3 ± 3.1 kg/m(2)) were recorded continuously at a defined skin area at the radial forearm. Under standardized conditions, microcirculatory measurements were performed using a combined laser Doppler and photospectrometry system. After baseline measurement, CAP was applied by a DBD plasma device for 90 s to the same defined skin area of 22.5 cm(2). Immediately after the application cutaneous microcirculation was assessed for 30 min at the same site.

RESULTS

After CAP application, tissue oxygen saturation immediately increased by 24% (63.8 ± 13.8% from 51.4 ± 13.2% at baseline, p<0.001) and stayed significantly elevated for 8 min. Cutaneous blood flow increased by 73% (41.0 ± 31.2 AU from 23.7 ± 20.8 AU at baseline, p<0.001) and remained upregulated for 11 min. Furthermore, cutaneous blood flow showed two peaks at 14 (29.8 ± 25.0 AU, p=0.049) and 19 min (29.8 ± 22.6 AU, p=0.048) after treatment. Postcapillary venous filling pressure continuously increased, but showed no significant change vs. baseline in the non-specific BMI group. Subgroup analysis revealed that tissue oxygen saturation, postcapillary venous filling pressure and blood flow increased more in case of a lower BMI.

CONCLUSION

CAP increases cutaneous tissue oxygen saturation and capillary blood flow at the radial forearm of healthy volunteers. These results support recently published data on wound healing after CAP treatment. However, further studies are needed to determine if this treatment can improve the reduced microcirculation in diabetic foot ulcers. Moreover, repetitive application protocols have to be compared with a single session treatment approach.

Cold Plasma Inactivation of Bacterial Biofilms and Reduction of Quorum Sensing Regulated Virulence Factors

The main objectives of this work were to investigate the effect of atmospheric cold plasma (ACP) against a range of microbial biofilms commonly implicated in foodborne and healthcare associated human infections and against P. aeruginosa quorum sensing (QS)-regulated virulence factors, such as pyocyanin, elastase (Las B) and biofilm formation capacity post-ACP treatment. The effect of processing factors, namely treatment time and mode of plasma exposure on antimicrobial activity of ACP were also examined. Antibiofilm activity was assessed for E. coli, L. monocytogenes and S. aureus in terms of reduction of culturability and retention of metabolic activity using colony count and XTT assays, respectively. All samples were treated ‘inpack’ using sealed polypropylene containers with a high voltage dielectric barrier discharge ACP generated at 80 kV for 0, 60, 120 and 300 s and a post treatment storage time of 24 h. According to colony counts, ACP treatment for 60 s reduced populations of E. coli to undetectable levels, whereas 300 s was necessary to significantly reduce populations of L. monocytogenes and S. aureus biofilms. The results obtained from XTT assay indicated possible induction of viable but non culturable state of bacteria. With respect to P. aeruginosa QS-related virulence factors, the production of pyocyanin was significantly inhibited after short treatment times, but reduction of elastase was notable only after 300 s and no reduction in actual biofilm formation was achieved post-ACP treatment. Importantly, reduction of virulence factors was associated with reduction of the cytotoxic effects of the bacterial supernatant on CHO-K1 cells, regardless of mode and duration of treatment. The results of this study point to ACP technology as an effective strategy for inactivation of established biofilms and may play an important role in attenuation of virulence of pathogenic bacteria. Further investigation is warranted to propose direct evidence for the inhibition of QS and mechanisms by which this may occur.

Atmospheric-Pressure Cold Plasma Induces Transcriptional Changes in Ex Vivo Human Corneas

Background

Atmospheric pressure cold plasma (APCP) might be considered a novel tool for tissue disinfection in medicine since the active chemical species produced by low plasma doses, generated by ionizing helium gas in air, induces reactive oxygen species (ROS) that kill microorganisms without substantially affecting human cells.

Objectives

In this study, we evaluated morphological and functional changes in human corneas exposed for 2 minutes (min) to APCP and tested if the antioxidant n-acetyl l-cysteine (NAC) was able to inhibit or prevent damage and cell death.

Results

Immunohistochemistry and western blotting analyses of corneal tissues collected at 6 hours (h) post-APCP treatment demonstrated no morphological tissue changes, but a transient increased expression of OGG1 glycosylase that returned to control levels in 24 h. Transcriptome sequencing and quantitative real time PCR performed on different corneas revealed in the treated corneas many differentially expressed genes: namely, 256 and 304 genes showing expression changes greater than ± 2 folds in the absence and presence of NAC, respectively. At 6 h post-treatment, the most over-expressed gene categories suggested an active or enhanced cell functioning, with only a minority of genes specifically concerning oxidative DNA damage and repair showing slight over-expression values (<2 folds). Moreover, time-related expression analysis of eight genes up-regulated in the APCP-treated corneas overall demonstrated the return to control expression levels after 24 h.

Conclusions

These findings of transient oxidative stress accompanied by wide-range transcriptome adjustments support the further development of APCP as an ocular disinfectant.

Clinical use of cold atmospheric pressure argon plasma in chronic leg ulcers: A pilot study

OBJECTIVE

In the age of multiresistant microbes and the increasing lack of efficient antibiotics, conventional antiseptics play a critical role in the prevention and therapy of wound infections. Recent studies have demonstrated the antiseptic effects of cold atmospheric pressure plasma (APP). In this pilot, study we investigate the overall suitability of one of the first APP sources for wound treatment focusing on its potential antimicrobial effects.

METHOD

The wound closure rate and the bacterial colonisation of the wounds were investigated. Patients suffering from chronic leg ulcers were treated in a clinical controlled monocentric trial with either APP or octenidine (OCT). In patients who presented with more than one ulceration in different locations, one was treated with APP and the other one with OCT. Each group was treated three times a week over a period of two weeks. The antimicrobial efficacy was evaluated immediately after and following two weeks of treatment.

RESULTS

Wounds treated with OCT showed a significantly higher microbial reduction (64%) compared to wounds treated with APP (47%) immediately after the treatment. Over two weeks of antiseptic treatment the bacterial density was reduced within the OCT group (-35%) compared to a slight increase in bacterial density in the APP-treated group (+12%). Clinically, there were no signs of delayed wound healing observed in either group and both treatments were well tolerated.

CONCLUSION

The immediate antimicrobial effects of the APP prototype source were almost comparable to OCT without any signs of cytotoxicity. This pilot study is limited by current configurations of the plasma source, where the narrow plasma beam made it difficult to cover larger wound surface areas and in order to avoid untreated areas of the wound bed, smaller wounds were assigned to the APP-treatment group. This limits the significance of AAP-related effects on the wound healing dynamics, as smaller wounds tend to heal faster than larger wounds. However, clinical wound healing studies on a larger scale now seem justifiable. A more advanced plasma source prototype allowing the treatment of larger wounds will address APP's influence on healing dynamics, synergetic treatment with current antiseptics and effects on multiresistant bacteria.

Pseudomonas aeruginosa Biofilm Response and Resistance to Cold Atmospheric Pressure Plasma Is Linked to the Redox-Active Molecule Phenazine

Pseudomonas aeruginosa is an important opportunistic pathogen displaying high antibiotic resistance. Its resistance is in part due to its outstanding ability to form biofilms on a range of biotic and abiotic surfaces leading to difficult-to-treat, often long-term infections. Cold atmospheric plasma (CAP) is a new, promising antibacterial treatment to combat antibiotic-resistant bacteria. Plasma is ionized gas that has antibacterial properties through the generation of a mix of reactive oxygen and nitrogen species (RONS), excited molecules, charged particles and UV photons. Our results show the efficient removal of P. aeruginosa biofilms using a plasma jet (kINPen med), with no viable cells detected after 5 min treatment and no attached biofilm cells visible with confocal microscopy after 10 min plasma treatment. Because of its multi-factorial action, it is widely presumed that the development of bacterial resistance to plasma is unlikely. However, our results indicate that a short plasma treatment (3 min) may lead to the emergence of a small number of surviving cells exhibiting enhanced resistance to subsequent plasma exposure. Interestingly, these cells also exhibited a higher degree of resistance to hydrogen peroxide. Whole genome comparison between surviving cells and control cells revealed 10 distinct polymorphic regions, including four belonging to the redox active, antibiotic pigment phenazine. Subsequently, the interaction between phenazine production and CAP resistance was demonstrated in biofilms of transposon mutants disrupted in different phenazine pathway genes which exhibited significantly altered sensitivity to CAP.

On the effect of serum on the transport of reactive oxygen species across phospholipid membranes

The transport of plasma generated reactive oxygen species (ROS) across a simple phospholipid membrane mimic of a (real) cell was investigated. Experiments were performed in cell culture media (Dulbecco's modified Eagle's medium, DMEM), with and without 10% serum. A (broad spectrum) ROS reporter dye, 2,7-dichlorodihydrofluorescein (DCFH), was used to detect the generation of ROS by a helium (He) plasma jet in DMEM using free DCFH and with DCFH encapsulated inside phospholipid membrane vesicles dispersed in DMEM. The authors focus on the concentration and on the relative rates (arbitrary units) for oxidation of DCFH [or the appearance of the oxidized product 2,7-dichlorofluorescein (DCF)] both in solution and within vesicles. In the first 1 h following plasma exposure, the concentration of free DCF in DMEM was ~15× greater in the presence of serum (cf. to the serum-free DMEM control). The DCF in vesicles was ~2× greater in DMEM containing serum compared to the serum-free DMEM control. These data show that serum enhances plasma ROS generation in DMEM. As expected, the role of the phospholipid membrane was to reduce the rate of oxidation of the encapsulated DCFH (with and without serum). And the efficiency of ROS transport into vesicles was lower in DMEM containing serum (at 4% efficiency) when compared to serum-free DMEM (at 32% efficiency). After 1 h, the rate of DCFH oxidation was found to have significantly reduced. Based upon a synthesis of these data with results from the open literature, the authors speculate on how the components of biological fluid and cellular membranes might affect the kinetics of consumption of plasma generated ROS.

Atmospheric pressure nonthermal plasmas for bacterial biofilm prevention and eradication

Biofilms are three-dimensional structures formed by surface-attached microorganisms and their extracellular products. Biofilms formed by pathogenic microorganisms play an important role in human diseases. Higher resistance to antimicrobial agents and changes in microbial physiology make treating biofilm infections very complex. Atmospheric pressure nonthermal plasmas (NTPs) are a novel and powerful tool for antimicrobial treatment. The microbicidal activity of NTPs has an unspecific character due to the synergetic actions of bioactive components of the plasma torch, including charged particles, reactive species, and UV radiation. This review focuses on specific traits of biofilms, their role in human diseases, and those effects of NTP that are helpful for treating biofilm infections. The authors discuss NTP-based strategies for biofilm control, such as surface modifications to prevent bacterial adhesion, killing bacteria in biofilms, and biofilm destruction with NTPs. The unspecific character of microbicidal activity, proven polymer modification and destruction abilities, low toxicity for human tissues and absence of long-living toxic compounds make NTPs a very promising tool for biofilm prevention and control.

Investigation of the antimicrobial activity at safe levels for eukaryotic cells of a low power atmospheric pressure inductively coupled plasma source

Low power atmospheric pressure inductively coupled thermal plasma sources integrated with a quenching device (cold ICP) for the efficient production of biologically active agents have been recently developed for potential biomedical applications. In the present work, in vitro experiments aimed at assessing the decontamination potential of a cold ICP source were carried out on bacteria typically associated with chronic wounds and designed to represent a realistic wound environment; further in vitro experiments were performed to investigate the effects of plasma-irradiated physiological saline solution on eukaryotic cells viability. A thorough characterization of the plasma source and process, for what concerns ultraviolet (UV) radiation and nitric oxide production as well as the variation of pH and the generation of nitrates and nitrites in the treated liquid media, was carried out to garner fundamental insights that could help the interpretation of biological experiments. Direct plasma treatment of bacterial cells, performed at safe level of UV radiation, induces a relevant decontamination, both on agar plate and in physiological saline solution, after just 2 min of treatment. Furthermore, the indirect treatment of eukaryotic cells, carried out by covering them with physiological saline solution irradiated by plasma, in the same conditions selected for the direct treatment of bacterial cells does not show any noticeable adverse effect to their viability. Some considerations regarding the role of the UV radiation on the decontamination potential of bacterial cells and the viability of the eukaryotic ones will be presented. Moreover, the effects of pH variation, nitrate and nitrite concentrations of the plasma-irradiated physiological saline solution on the decontamination of bacterial suspension and on the viability of eukaryotic cells subjected to the indirect treatment will be discussed. The obtained results will be used to optimize the design of the ICP source for an effective production of reactive species, while keeping effluent temperature and UV radiation at values compatible with biomedical treatments.

Combined antibacterial effects of tissue-tolerable plasma and a modern conventional liquid antiseptic on chronic wound treatment

Potential antimicrobial effects of sequential applications of tissue-tolerable plasma (TTP) and the conventional liquid antiseptic octenidine dihydrochloride (ODC) were investigated. 34 patients with chronic leg ulcers were treated with TTP, ODC or a combination of both. The bacterial colonization was measured semi-quantitatively before and immediately after treatment and changes in the microbial strains' compositions before and after antiseptic treatments were analyzed. All antiseptic procedures reduced the bacterial counts significantly. The sequential application of TTP and ODC displayed the highest antimicrobial efficacy. Me combined use of TTP and conventional antiseptics might represent the most efficient strategy for antiseptic treatment of chronic wounds.

Bactericidal efficacy of atmospheric pressure non-thermal plasma (APNTP) against the ESKAPE pathogens

The emergence of multidrug-resistant pathogens within the clinical environment is presenting a mounting problem in hospitals worldwide. The 'ESKAPE' pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) have been highlighted as a group of causative organisms in a majority of nosocomial infections, presenting a serious health risk due to widespread antimicrobial resistance. The stagnating pipeline of new antibiotics requires alternative approaches to the control and treatment of nosocomial infections. Atmospheric pressure non-thermal plasma (APNTP) is attracting growing interest as an alternative infection control approach within the clinical setting. This study presents a comprehensive bactericidal assessment of an in-house-designed APNTP jet both against biofilms and planktonic bacteria of the ESKAPE pathogens. Standard plate counts and the XTT metabolic assay were used to evaluate the antibacterial effect of APNTP, with both methods demonstrating comparable eradication times. APNTP exhibited rapid antimicrobial activity against all of the ESKAPE pathogens in the planktonic mode of growth and provided efficient and complete eradication of ESKAPE pathogens in the biofilm mode of growth within 360s, with the exception of A. baumannii where a >4log reduction in biofilm viability was observed. This demonstrates its effectiveness as a bactericidal treatment against these pathogens and further highlights its potential application in the clinical environment for the control of highly antimicrobial-resistant pathogens.

MS2 virus inactivation by atmospheric-pressure cold plasma using different gas carriers and power levels

In this study, airborne MS2 bacteriophages were exposed for subsecond time intervals to atmospheric-pressure cold plasma (APCP) produced using different power levels (20, 24, and 28 W) and gas carriers (ambient air, Ar-O2 [2%, vol/vol], and He-O2 [2%, vol/vol]). In addition, waterborne MS2 viruses were directly subjected to the APCP treatment for up to 3 min. MS2 viruses with and without the APCP exposure were examined by scanning electron microscopy (SEM), reverse transcription-PCR (RT-PCR), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Viral inactivation was shown to exhibit linear relationships with the APCP generation power and exposure time (R(2) > 0.95 for all energy levels tested) up to 95% inactivation (1.3-log reduction) after a subsecond airborne exposure at 28 W; about the same inactivation level was achieved for waterborne viruses with an exposure time of less than 1 min. A larger amount of reactive oxygen species (ROS), such as atomic oxygen, in APCP was detected for a higher generation power with Ar-O2 and He-O2 gas carriers. SEM images, SDS-PAGE, and agarose gel analysis of exposed waterborne viruses showed various levels of damage to both surface proteins and their related RNA genes after the APCP exposure, thus leading to the loss of their viability and infectivity.

Nonthermal plasma--A tool for decontamination and disinfection

By definition, the nonthermal plasma (NTP) is partially ionized gas where the energy is stored mostly in the free electrons and the overall temperature remains low. NTP is widely used for many years in various applications such as low-temperature plasma chemistry, removal of gaseous pollutants, in gas-discharge lamps or surface modification. However, during the last ten years, NTP usage expanded to new biological areas of application like plasma microorganisms' inactivation, ready-to-eat food preparation, biofilm degradation or in healthcare, where it seems to be important for the treatment of cancer cells and in the initiation of apoptosis, prion inactivation, prevention of nosocomial infections or in the therapy of infected wounds. These areas are presented and documented in this paper as a review of representative publications.

Non-thermal atmospheric-pressure plasma possible application in wound healing

Non-thermal atmospheric-pressure plasma, also named cold plasma, is defined as a partly ionized gas. Therefore, it cannot be equated with plasma from blood; it is not biological in nature. Non-thermal atmospheric-pressure plasma is a new innovative approach in medicine not only for the treatment of wounds, but with a wide-range of other applications, as e.g. topical treatment of other skin diseases with microbial involvement or treatment of cancer diseases. This review emphasizes plasma effects on wound healing. Non-thermal atmospheric-pressure plasma can support wound healing by its antiseptic effects, by stimulation of proliferation and migration of wound relating skin cells, by activation or inhibition of integrin receptors on the cell surface or by its pro-angiogenic effect. We summarize the effects of plasma on eukaryotic cells, especially on keratinocytes in terms of viability, proliferation, DNA, adhesion molecules and angiogenesis together with the role of reactive oxygen species and other components of plasma. The outcome of first clinical trials regarding wound healing is pointed out.

Cell death induced by ozone and various non-thermal plasmas: therapeutic perspectives and limitations

Non-thermal plasma has been recognized as a promising tool across a vast variety of biomedical applications, with the potential to create novel therapeutic methods. However, the understanding of the molecular mechanisms behind non-thermal plasma cellular effects remains a significant challenge. In this study, we show how two types of different non-thermal plasmas induce cell death in mammalian cell cultures via the formation of multiple intracellular reactive oxygen/nitrogen species. Our results showed a discrepancy in the superoxide accumulation and lysosomal activity in response to air and helium plasma, suggesting that triggered signalling cascades might be grossly different between different plasmas. In addition, the effects of ozone, a considerable component of non-thermal plasma, have been simultaneously evaluated and have revealed much faster and higher cytotoxic effects. Our findings offer novel insight into plasma-induced cellular responses, and provide a basis for better controlled biomedical applications.

Persistent effectivity of gas plasma-treated, long time-stored liquid on epithelial cell adhesion capacity and membrane morphology

Research in plasma medicine includes a major interest in understanding gas plasma-cell interactions. The immediate application of gas plasma in vitro inhibits cell attachment, vitality and cell-cell contacts via the liquid. Interestingly, in our novel experiments described here we found that the liquid-mediated plasma effect is long-lasting after storage up to seven days; i. e. the liquid preserves the characteristics once induced by the argon plasma. Therefore, the complete Dulbecco's Modified Eagle cell culture medium was argon plasma-treated (atmospheric pressure, kINPen09) for 60 s, stored for several days (1, 4 and 7 d) at 37°C and added to a confluent mouse hepatocyte epithelial cell (mHepR1) monolayer. Impaired tight junction architecture as well as shortened microvilli on the cell membrane could be observed, which was accompanied by the loss of cell adhesion capacity. Online-monitoring of vital cells revealed a reduced cell respiration. Our first time-dependent analysis of plasma-treated medium revealed that temperature, hydrogen peroxide production, pH and oxygen content can be excluded as initiators of cell physiological and morphological changes. The here observed persisting biological effects in plasma-treated liquids could open new medical applications in dentistry and orthopaedics.

Atmospheric-pressure plasma jet induces DNA double-strand breaks that require a Rad51-mediated homologous recombination for repair in Saccharomyces cerevisiae

Non-thermal plasma generated under atmospheric pressure produces a mixture of chemically reactive molecules and has been developed for a number of biomedical applications. Recently, plasma jet has been proposed as novel cancer therapies based on the observation that free radicals generated by plasma jet induce mitochondria-mediated apoptotic cell death. We show here that air plasma jet induces DNA double-strand breaks (DSBs) in yeast chromosomes leading to genomic instability and loss of viability, which are alleviated by Rad51, the yeast homolog of Escherichiacoli RecA recombinase, through DNA damage repair by a homologous recombination (HR) process. Hypersensitivity of rad51 mutant to air plasma was not restored by antioxidant treatment unlike sod1 mutant that was highly sensitive to reactive oxygen species (ROS) challenge, suggesting that plasma jet induces DSB-mediated cell death independent of ROS generation. These results may provide a new insight into the mechanism of air plasma jet-induced cell death.

Recent developments in topical wound therapy: impact of antimicrobiological changes and rebalancing the wound milieu

Wound therapy improves every year by developing new wound treatment options or by advancing already existing wound materials, for example, adding self-releasing analgesic drugs or growth factors to wound dressings, or by binding and inactivating excessive proteases. Also new dressing materials based on silk fibers and enhanced methods to reduce bacterial burden, for example, cold argon plasma, might help to fasten wound healing.

Atmospheric pressure plasmas: infection control and bacterial responses

Cold atmospheric pressure plasma (APP) is a recent, cutting-edge antimicrobial treatment. It has the potential to be used as an alternative to traditional treatments such as antibiotics and as a promoter of wound healing, making it a promising tool in a range of biomedical applications with particular importance for combating infections. A number of studies show very promising results for APP-mediated killing of bacteria, including removal of biofilms of pathogenic bacteria such as Pseudomonas aeruginosa. However, the mode of action of APP and the resulting bacterial response are not fully understood. Use of a variety of different plasma-generating devices, different types of plasma gases and different treatment modes makes it challenging to show reproducibility and transferability of results. This review considers some important studies in which APP was used as an antibacterial agent, and specifically those that elucidate its mode of action, with the aim of identifying common bacterial responses to APP exposure. The review has a particular emphasis on mechanisms of interactions of bacterial biofilms with APP.

Cold atmospheric plasma devices for medical issues

Cold atmospheric plasma science is an innovative upcoming technology for the medical sector. The plasma composition and subsequent effects on cells, tissues and pathogens can vary enormously depending on the plasma source, the plasma settings and the ambient conditions. Cold atmospheric plasmas consist of a highly reactive mix of ions and electrons, reactive molecules, excited species, electric fields and to some extent also UV radiation. In the last year, this partly ionized gas has been demonstrated to have a broad antimicrobial activity, while resistance and resistance development are unlikely. Furthermore, recent research has indicated that plasmas also have a strong influence on various cell lines and cell functions, including anticancer properties. This review summarizes the major plasma designs available and their main benefits, as well as assessing possible risks of this new technology.

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/cm(2), argon with admixed oxygen 3 log10 CFU/cm(2), and with increased gas humidity 2.7 log10 CFU/cm(2) 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.

Physiological and transcriptional response of Bacillus cereus treated with low-temperature nitrogen gas plasma

AIMS

This study was conducted to investigate the inactivation kinetics of Bacillus cereus vegetative cells upon exposure to low-temperature nitrogen gas plasma and to reveal the mode of inactivation by transcriptome profiling.

METHODS AND RESULTS

Exponentially growing B. cereus cells were filtered and put on agar plates. The plates, carrying the filters with the vegetative cells, were placed into low-temperature nitrogen gas plasma at atmospheric pressure. After different exposure times, the cells were harvested for RNA extraction and enumeration. The RNA was used to perform whole-transcriptome profiling using DNA microarrays. The transcriptome profile showed a large overlap with profiles obtained from conditions generating reactive oxygen species in B. cereus. However, excess radicals such as peroxynitrite, hydroxyl and superoxide could not be detected using radical-specific fluorescence staining. Lack of UV-specific responses including factors involved in DNA damage repair is in line with the absence of UV-specific emission in the afterglow of the nitrogen gas plasma as analysed using optical emission spectroscopy (OES).

CONCLUSIONS

Antibacterial activity of nitrogen gas plasma is not based on UV radiation. Exposure to nitrogen gas plasma leads to oxidative stress and inactivation of targeted cells. A secondary oxidative stress with the indicative formation of reactive oxygen species within cells could not be observed.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study represents the first investigation of differential gene expression on a genome-wide scale in B. cereus following nitrogen gas plasma exposure. This study may help to design economically feasible, safe and effective plasma decontamination devices.

Differential influence of components resulting from atmospheric-pressure plasma on integrin expression of human HaCaT keratinocytes

Adequate chronic wound healing is a major problem in medicine. A new solution might be non-thermal atmospheric-pressure plasma effectively inactivating microorganisms and influencing cells in wound healing. Plasma components as, for example, radicals can affect cells differently. HaCaT keratinocytes were treated with Dielectric Barrier Discharge plasma (DBD/air, DBD/argon), ozone or hydrogen peroxide to find the components responsible for changes in integrin expression, intracellular ROS formation or apoptosis induction. Dependent on plasma treatment time reduction of recovered cells was observed with no increase of apoptotic cells, but breakdown of mitochondrial membrane potential. DBD/air plasma increased integrins and intracellular ROS. DBD/argon caused minor changes. About 100 ppm ozone did not influence integrins. Hydrogen peroxide caused similar effects compared to DBD/air plasma. In conclusion, effects depended on working gas and exposure time to plasma. Short treatment cycles did neither change integrins nor induce apoptosis or ROS. Longer treatments changed integrins as important for influencing wound healing. Plasma effects on integrins are rather attributed to induction of other ROS than to generation of ozone. Changes of integrins by plasma may provide new solutions of improving wound healing, however, conditions are needed which allow initiating the relevant influence on integrins without being cytotoxic to cells.

Accelerated mice skin acute wound healing in vivo by combined treatment of argon and helium plasma needle

BACKGROUND AND AIMS

The efficacy of a direct application of plasma needle to in vivo wound healing was experimentally studied in mice. This kind of plasma has achieved considerable success in blood coagulation and tissue restoration in mice. In the development of the present study, an argon plasma needle was chosen for coagulation purposes, whereas for healing purposes, a helium plasma needle was used.

METHODS

Treatment was applied with a plasma needle produced by argon and helium to a wound induced in laboratory mice. Tissue regeneration was carried out by three argon plasma treatments with 0.5 SLPM flow for 1 min and three treatments of helium with 1.5 SLPM flow. Intervals between each treatment were 5 min and 60 min for argon and helium plasmas, respectively, thus completing a total treatment time of 180 min. Histological sections were performed to corroborate the internal bleeding and tissue regeneration.

RESULTS

After three treatments with argon plasma, the blood produced in the wound was coagulated and protein material appeared. By means of treatment with helium plasma, an approach of the wound edges was produced until the conclusion thereof. These results were corroborated histologically.

CONCLUSIONS

This type of acceleration during the skin wound healing process can be attributed to the formation of reactive species such as NO, which were increased in the helium plasma needle with respect to the argon plasma needle.

Atmospheric pressure plasma: a high-performance tool for the efficient removal of biofilms

Introduction

The medical use of non-thermal physical plasmas is intensively investigated for sterilization and surface modification of biomedical materials. A further promising application is the removal or etching of organic substances, e.g., biofilms, from surfaces, because remnants of biofilms after conventional cleaning procedures are capable to entertain inflammatory processes in the adjacent tissues. In general, contamination of surfaces by micro-organisms is a major source of problems in health care. Especially biofilms are the most common type of microbial growth in the human body and therefore, the complete removal of pathogens is mandatory for the prevention of inflammatory infiltrate. Physical plasmas offer a huge potential to inactivate micro-organisms and to remove organic materials through plasma-generated highly reactive agents.

Method

In this study a Candida albicans biofilm, formed on polystyrene (PS) wafers, as a prototypic biofilm was used to verify the etching capability of the atmospheric pressure plasma jet operating with two different process gases (argon and argon/oxygen mixture). The capability of plasma-assisted biofilm removal was assessed by microscopic imaging.

Results

The Candida albicans biofilm, with a thickness of 10 to 20 µm, was removed within 300 s plasma treatment when oxygen was added to the argon gas discharge, whereas argon plasma alone was practically not sufficient in biofilm removal. The impact of plasma etching on biofilms is localized due to the limited presence of reactive plasma species validated by optical emission spectroscopy.

Cold atmospheric air plasma sterilization against spores and other microorganisms of clinical interest

Physical cold atmospheric surface microdischarge (SMD) plasma operating in ambient air has promising properties for the sterilization of sensitive medical devices where conventional methods are not applicable. Furthermore, SMD plasma could revolutionize the field of disinfection at health care facilities. The antimicrobial effects on Gram-negative and Gram-positive bacteria of clinical relevance, as well as the fungus Candida albicans, were tested. Thirty seconds of plasma treatment led to a 4 to 6 log(10) CFU reduction on agar plates. C. albicans was the hardest to inactivate. The sterilizing effect on standard bioindicators (bacterial endospores) was evaluated on dry test specimens that were wrapped in Tyvek coupons. The experimental D(23)(°)(C) values for Bacillus subtilis, Bacillus pumilus, Bacillus atrophaeus, and Geobacillus stearothermophilus were determined as 0.3 min, 0.5 min, 0.6 min, and 0.9 min, respectively. These decimal reduction times (D values) are distinctly lower than D values obtained with other reference methods. Importantly, the high inactivation rate was independent of the material of the test specimen. Possible inactivation mechanisms for relevant microorganisms are briefly discussed, emphasizing the important role of neutral reactive plasma species and pointing to recent diagnostic methods that will contribute to a better understanding of the strong biocidal effect of SMD air plasma.

Decolonisation of MRSA, S. aureus and E. coli by cold-atmospheric plasma using a porcine skin model in vitro

In the last twenty years new antibacterial agents approved by the U.S. FDA decreased whereas in parallel the resistance situation of multi-resistant bacteria increased. Thus, community and nosocomial acquired infections of resistant bacteria led to a decrease in the efficacy of standard therapy, prolonging treatment time and increasing healthcare costs. Therefore, the aim of this work was to demonstrate the applicability of cold atmospheric plasma for decolonisation of Gram-positive (Methicillin-resistant Staphylococcus aureus (MRSA), Methicillin-sensitive Staphylococcus aureus) and Gram-negative bacteria (E. coli) using an ex vivo pig skin model. Freshly excised skin samples were taken from six month old female pigs (breed: Pietrain). After application of pure bacteria on the surface of the explants these were treated with cold atmospheric plasma for up to 15 min. Two different plasma devices were evaluated. A decolonisation efficacy of 3 log₁₀ steps was achieved already after 6 min of plasma treatment. Longer plasma treatment times achieved a killing rate of 5 log₁₀ steps independently from the applied bacteria strains. Histological evaluations of untreated and treated skin areas upon cold atmospheric plasma treatment within 24 h showed no morphological changes as well as no significant degree of necrosis or apoptosis determined by the TUNEL-assay indicating that the porcine skin is still vital. This study demonstrates for the first time that cold atmospheric plasma is able to very efficiently kill bacteria applied to an intact skin surface using an ex vivo porcine skin model. The results emphasize the potential of cold atmospheric plasma as a new possible treatment option for decolonisation of human skin from bacteria in patients in the future without harming the surrounding tissue.

Contact-free inactivation of Candida albicans biofilms by cold atmospheric air plasma

Candida albicans is one of the main species able to form a biofilm on almost any surface, causing both skin and superficial mucosal infections. The worldwide increase in antifungal resistance has led to a decrease in the efficacy of standard therapies, prolonging treatment time and increasing health care costs. Therefore, the aim of this work was to demonstrate the applicability of atmospheric plasma at room temperature for inactivating C. albicans growing in biofilms without thermally damaging heat-sensitive materials. This so-called cold atmospheric plasma is produced by applying high voltage to accelerate electrons, which ionize the surrounding air, leading to the production of charged particles, reactive species, and photons. A newly developed plasma device was used, which exhibits a large plasma-generating surface area of 9 by 13 cm (117 cm(2)). Different time points were selected to achieve an optimum inactivation efficacy range of ≥3 log(10) to 5 log(10) reduction in CFU per milliliter, and the results were compared with those of 70% ethanol. The results obtained show that contact-free antifungal inactivation of Candida biofilms by cold atmospheric plasma is a promising tool for disinfection of surfaces (and items) in both health care settings and the food industry, where ethanol disinfection should be avoided.