Bactericidal efficacy of cold atmospheric plasma treatment against multidrug-resistant Pseudomonas aeruginosa

Low-Temperature Plasma Techniques in Biomedical Applications and Therapeutics: An Overview

Plasma, the fourth fundamental state of matter, comprises charged species and electrons, and it is a fascinating medium that is spread over the entire visible universe. In addition to that, plasma can be generated artificially under appropriate laboratory techniques. Artificially generated thermal or hot plasma has applications in heavy and electronic industries; however, the non-thermal (cold atmospheric or low temperature) plasma finds its applications mainly in biomedicals and therapeutics. One of the important characteristics of LTP is that the constituent particles in the plasma stream can often maintain an overall temperature of nearly room temperature, even though the thermal parameters of the free electrons go up to 1 to 10 keV. The presence of reactive chemical species at ambient temperature and atmospheric pressure makes LTP a bio-tolerant tool in biomedical applications with many advantages over conventional techniques. This review presents some of the important biomedical applications of cold-atmospheric plasma (CAP) or low-temperature plasma (LTP) in modern medicine, showcasing its effect in antimicrobial therapy, cancer treatment, drug/gene delivery, tissue engineering, implant modifications, interaction with biomolecules, etc., and overviews some present challenges in the field of plasma medicine.

Cold atmospheric pressure plasma-antibiotic synergy in Pseudomonas aeruginosa biofilms is mediated via oxidative stress response

Cold atmospheric-pressure plasma (CAP) has emerged as a potential alternative or adjuvant to conventional antibiotics for the treatment of bacterial infections, including those caused by antibiotic-resistant pathogens. The potential of sub-lethal CAP exposures to synergise conventional antimicrobials for the eradication of Pseudomonas aeruginosa biofilms is investigated in this study. The efficacy of antimicrobials following or in the absence of sub-lethal CAP pre-treatment in P. aeruginosa biofilms was assessed. CAP pre-treatment resulted in an increase in both planktonic and biofilm antimicrobial sensitivity for all three strains tested (PAO1, PA14, and PA10548), with both minimum inhibitory concentrations (MICs) and minimum biofilm eradication concentrations (MBECs) of individual antimicrobials, being significantly reduced following CAP pre-treatment of the biofilm (512-fold reduction with ciprofloxacin/gentamicin; and a 256-fold reduction with tobramycin). At all concentrations of antimicrobial used, the combination of sub-lethal CAP exposure and antimicrobials was effective at increasing time-to-peak metabolism, as measured by isothermal microcalorimetry, again indicating enhanced susceptibility. CAP is known to damage bacterial cell membranes and DNA by causing oxidative stress through the in situ generation of reactive oxygen and nitrogen species (RONS). While the exact mechanism is not clear, oxidative stress on outer membrane proteins is thought to damage/perturb cell membranes, confirmed by ATP and LDH leakage, allowing antimicrobials to penetrate the bacterial cell more effectively, thus increasing bacterial susceptibility. Transcriptomic analysis, reveals that cold-plasma mediated oxidative stress caused upregulation of P. aeruginosa superoxide dismutase, cbb3 oxidases, catalases, and peroxidases, and upregulation in denitrification genes, suggesting that P. aeruginosa uses these enzymes to degrade RONS and mitigate the effects of cold plasma mediated oxidative stress. CAP treatment also led to an increased production of the signalling molecule ppGpp in P. aeruginosa, indicative of a stringent response being established. Although we did not directly measure persister cell formation, this stringent response may potentially be associated with the formation of persister cells in biofilm cultures. The production of ppGpp and polyphosphate may be associated with protein synthesis inhibition and increase efflux pump activity, factors which can result in antimicrobial tolerance. The transcriptomic analysis also showed that by 6 h post-treatment, there was downregulation in ribosome modulation factor, which is involved in the formation of persister cells, suggesting that the cells had begun to resuscitate/recover. In addition, CAP treatment at 4 h post-exposure caused downregulation of the virulence factors pyoverdine and pyocyanin; by 6 h post-exposure, virulence factor production was increasing. Transcriptomic analysis provides valuable insights into the mechanisms by which P. aeruginosa biofilms exhibits enhanced susceptibility to antimicrobials. Overall, these findings suggest, for the first time, that short CAP sub-lethal pre-treatment can be an effective strategy for enhancing the susceptibility of P. aeruginosa biofilms to antimicrobials and provides important mechanistic insights into cold plasma-antimicrobial synergy. Transcriptomic analysis of the response to, and recovery from, sub-lethal cold plasma exposures in P. aeruginosa biofilms improves our current understanding of cold plasma biofilm interactions.

Effects and Mechanisms of Non-Thermal Plasma-Mediated ROS and Its Applications in Animal Husbandry and Biomedicine

Non-thermal plasma (NTP) is an ionized gas composed of neutral and charged reactive species, electric fields, and ultraviolet radiation. NTP presents a relatively low discharge temperature because it is characterized by the fact that the temperature values of ions and neutral particles are much lower than that of electrons. Reactive species (atoms, radicals, ions, electrons) are produced in NTP and delivered to biological objects induce a set of biochemical processes in cells or tissues. NTP can mediate reactive oxygen species (ROS) levels in an intensity- and time-dependent manner. ROS homeostasis plays an important role in animal health. Relatively low or physiological levels of ROS mediated by NTP promote cell proliferation and differentiation, while high or excessive levels of ROS mediated by NTP cause oxidative stress damage and even cell death. NTP treatment under appropriate conditions not only produces moderate levels of exogenous ROS directly and stimulates intracellular ROS generation, but also can regulate intracellular ROS levels indirectly, which affect the redox state in different cells and tissues of animals. However, the treatment condition of NTP need to be optimized and the potential mechanism of NTP-mediated ROS in different biological targets is still unclear. Over the past ten decades, interest in the application of NTP technology in biology and medical sciences has been rapidly growing. There is significant optimism that NTP can be developed for a wide range of applications such as wound healing, oral treatment, cancer therapy, and biomedical materials because of its safety, non-toxicity, and high efficiency. Moreover, the combined application of NTP with other methods is currently a hot research topic because of more effective effects on sterilization and anti-cancer abilities. Interestingly, NTP technology has presented great application potential in the animal husbandry field in recent years. However, the wide applications of NTP are related to different and complicated mechanisms, and whether NTP-mediated ROS play a critical role in its application need to be clarified. Therefore, this review mainly summarizes the effects of ROS on animal health, the mechanisms of NTP-mediated ROS levels through antioxidant clearance and ROS generation, and the potential applications of NTP-mediated ROS in animal growth and breeding, animal health, animal-derived food safety, and biomedical fields including would healing, oral treatment, cancer therapy, and biomaterials. This will provide a theoretical basis for promoting the healthy development of animal husbandry and the prevention and treatment of diseases in both animals and human beings.

Influence of cold atmospheric pressure plasma treatment of Spirulina platensis slurry over biomass characteristics

Cold atmospheric pressure plasma (CAPP) technique is an innovative non-thermal approach for food preservation and decontamination. This study aimed to evaluate the effect of CAPP power density on microorganism inactivation and quality of Spirulina platensis (S. platensis) slurry. 91.31 ± 1.61% of microorganism were inactivated within 2.02 ± 0.11 min by 26.67 W/g CAPP treatment under 50 ℃. Total phenolic, Chlorophyll-a (Chl-a), and carotenoids contents were increased by 20.51%, 63.55%, and 70.04% after 20.00 W/g CAPP treatment. Phycobiliproteins (PBPs), protein, intracellular polysaccharide, and moisture content of S. platensis was decreased, while vividness, lightness, color of yellow and green, antioxidant activity, Essential Amino Acid Index were enhanced after CAPP treatment. The nutrient release and filaments breakage of CAPP-treated S. platensis improved its bio-accessibility. The findings provided a deep understanding and insight into the influence of CAPP treatment on S. platensis, which were meaningful for optimizing its sterilization and drying processing condition.

The quality by design approach for optimization of slayer exciter based low power portable atmospheric plasma jet on bactericidal efficacy of Pseudomonas aeruginosa

A simple, portable, economical low-temperature atmospheric plasma (LTAP) for bactericidal efficacy of Gram-negative bacteria (Pseudomonas aeruginosa) with different carrier gases (argon, helium, and nitrogen) using the quality by design (QbD) approach, design of experiments (DoE), and response surface graphs (RSG) is presented. Box-Behnken design was used as the DoE to narrow down and further optimize the experimental factors of LTAP. Plasma exposure time, input DC voltage, and carrier gas flow rate were varied to examine the bactericidal efficacy using the zone of inhibition (ZOI). A higher bactericidal efficacy was achieved under the optimal bactericidal factors having ZOI of 50.837 ± 2.418 mm² with the plasma power density of 132 mW/cm³ for LTAP-Ar at 61.19 s, 14.8747 V, and 219.379 sccm than LTAP-He and LTAP-N₂ . The LTAP-Ar was further evaluated at different frequencies and probe lengths to achieve a ZOI of 58.237 ± 4.01 mm² .

Non-thermal plasma causes Pseudomonas aeruginosa biofilm release to planktonic form and inhibits production of Las-B elastase, protease and pyocyanin

The increasing risk of antibiotic failure in the treatment of Pseudomonas aeruginosa infections is largely related to the production of a wide range of virulence factors. The use of non-thermal plasma (NTP) is a promising alternative to antimicrobial treatment. Nevertheless, there is still a lack of knowledge about the effects of NTP on the virulence factors production. We evaluated the ability of four NTP-affected P. aeruginosa strains to re-form biofilm and produce Las-B elastase, proteases, lipases, haemolysins, gelatinase or pyocyanin. Highly strains-dependent inhibitory activity of NTP against extracellular virulence factors production was observed. Las-B elastase activity was reduced up to 82% after 15-min NTP treatment, protease activity and pyocyanin production by biofilm cells was completely inhibited after 60 min, in contrast to lipases and gelatinase production, which remained unchanged. However, for all strains tested, a notable reduction in biofilm re-development ability was depicted using spinning disc confocal microscopy. In addition, NTP exposure of mature biofilms caused disruption of biofilm cells and their dispersion into the environment, as shown by transmission electron microscopy. This appears to be a key step that could help overcome the high resistance of P. aeruginosa and its eventual elimination, for example in combination with antibiotics still highly effective against planktonic cells.

Implementation of a Non-Thermal Atmospheric Pressure Plasma for Eradication of Plant Pathogens from a Surface of Economically Important Seeds

Plant pathogenic bacteria cause significant economic losses in the global food production sector. To secure an adequate amount of high-quality nutrition for the growing human population, novel approaches need to be undertaken to combat plant disease-causing agents. As the currently available methods to eliminate bacterial phytopathogens are scarce, we evaluated the effectiveness and mechanism of action of a non-thermal atmospheric pressure plasma (NTAPP). It was ignited from a dielectric barrier discharge (DBD) operation in a plasma pencil, and applied for the first time for eradication of Dickeya and Pectobacterium spp., inoculated either on glass spheres or mung bean seeds. Furthermore, the impact of the DBD exposure on mung bean seeds germination and seedlings growth was estimated. The observed bacterial inactivation rates exceeded 3.07 logs. The two-minute DBD exposure stimulated by 3-4% the germination rate of mung bean seeds and by 13.4% subsequent early growth of the seedlings. On the contrary, a detrimental action of the four-minute DBD subjection on seed germination and early growth of the sprouts was noted shortly after the treatment. However, this effect was no longer observed or reduced to 9.7% after the 96 h incubation period. Due to the application of optical emission spectrometry (OES), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM), we found that the generated reactive oxygen and nitrogen species (RONS), i.e., N2, N2+, NO, OH, NH, and O, probably led to the denaturation and aggregation of DNA, proteins, and ribosomes. Furthermore, the cellular membrane disrupted, leading to an outflow of the cytoplasm from the DBD-exposed cells. This study suggests the potential applicability of NTAPPs as eco-friendly and innovative plant protection methods.

Applications of Cold Atmospheric Pressure Plasma Technology in Medicine, Agriculture and Food Industry

In recent years, cold atmospheric pressure plasma (CAPP) technology has received substantial attention due to its valuable properties including operational simplicity, low running cost, and environmental friendliness. Several different gases (air, nitrogen, helium, argon) and techniques (corona discharge, dielectric barrier discharge, plasma jet) can be used to generate plasma at atmospheric pressure and low temperature. Plasma treatment is routinely used in materials science to modify the surface properties (e.g., wettability, chemical composition, adhesion) of a wide range of materials (e.g., polymers, textiles, metals, glasses). Moreover, CAPP seems to be a powerful tool for the inactivation of various pathogens (e.g., bacteria, fungi, viruses) in the food industry (e.g., food and packing material decontamination, shelf life extension), agriculture (e.g., disinfection of seeds, fertilizer, water, soil) and medicine (e.g., sterilization of medical equipment, implants). Plasma medicine also holds great promise for direct therapeutic treatments in dentistry (tooth bleaching), dermatology (atopic eczema, wound healing) and oncology (melanoma, glioblastoma). Overall, CAPP technology is an innovative, powerful and effective tool offering a broad application potential. However, its limitations and negative impacts need to be determined in order to receive regulatory approval and consumer acceptance.

Effects of Plasma-Activated Water on Skin Wound Healing in Mice

Cold atmospheric plasma (CAP) has been widely used in biomedicine during the last two decades. While direct plasma treatment has been reported to promote wound healing, its application can be uneven and inconvenient. In this study, we first activated water with a portable dielectric barrier discharge plasma device and evaluated the inactivation effect of plasma-activated water (PAW) on several kinds of bacteria that commonly infect wounds. The results show that PAW can effectively inactivate these bacteria. Then, we activated tap water and examined the efficacy of PAW on wound healing in a mouse model of full-thickness skin wounds. We found that wound healing in mice treated with PAW was significantly faster compared with the control group. Histological analysis of the skin tissue of mice wounds showed a significant reduction in the number of inflammatory cells in the PAW treatment group. To identify the possible mechanism by which PAW promotes wound healing, we analyzed changes in the profiles of wound bacteria after PAW treatment. The results show that PAW can significantly reduce the abundance of wound bacteria in the treatment group. The results of biochemical blood tests and histological analysis of major internal organs in the mice show that PAW had no obvious side effects. Taken together, these results indicate that PAW may be a new and effective method for promoting wound healing without side effects.