Modeling the growth of Aspergillus brasiliensis affected by a nonthermal plasma.

AIM: The main objective of the study was to develop and validate a model for the growth of Aspergillus brasiliensis on surfaces, specifically on agar culture medium. An additional aim was to determine conditions for complete growth inhibition of this micromycete using two different nonthermal plasma (NTP) sources. METHODS AND RESULTS: The developed model uses two key parameters, namely the growth rate and growth delay, which depend on the cultivation temperature and the amount of inoculum. These parameters well describe the growth of A. brasiliensis and the effect of NTP on it. For complete fungus inactivation, a single 10-minute exposure to a diffuse coplanar surface barrier discharge was sufficient, while a point-to-ring corona discharge required several repeated 10-minute exposures at 24-h intervals. CONCLUSIONS: The article presents a model for simulating the surface growth of A. brasiliensis and evaluates the effectiveness of two NTP sources in deactivating fungi on agar media.

Non-Thermal Plasma Sources Based on Cometary and Point-to-Ring Discharges.

A non-thermal plasma (NTP) is a promising tool against the development of bacterial, viral, and fungal diseases. The recently revealed development of microbial resistance to traditional drugs has increased interest in the use of NTPs. We have studied and compared the physical and microbicidal properties of two types of NTP sources based on a cometary discharge in the point-to-point electrode configuration and a corona discharge in the point-to-ring electrode configuration. The electrical and emission properties of both discharges are reported. The microbicidal effect of NTP sources was tested on three strains of the bacterium Staphylococcus aureus (including the methicillin-resistant strain), the bacterium Pseudomonas aeruginosa, the yeast Candida albicans, and the micromycete Trichophyton interdigitale. In general, the cometary discharge is a less stable source of NTP and mostly forms smaller but more rapidly emerging inhibition zones on agar plates. Due to the point-to-ring electrode configuration, the second type of discharge has higher stability and provides larger affected but often not completely inhibited zones. However, after 60 min of exposure, the NTP sources based on the cometary and point-to-ring discharges showed a similar microbicidal effect for bacteria and an individual effect for microscopic fungi.

The red and blue luminescence in silicon nanocrystals with an oxidized, nitrogen-containing shell.

Traditionally, two classes of silicon nanocrystals (SiNCs) are recognized with respect to their light-emission properties. These are usually referred to as the "red" and the "blue" emitting SiNCs, based on the spectral region in which the larger part of their luminescence is concentrated. The origin of the "blue" luminescence is still disputed and is very probably different in different systems. One of the important contributions to the discussion about the origin of the "blue" luminescence was the finding that the exposure of SiNCs to even trace amounts of nitrogen in the presence of oxygen induces the "blue" emission, even in originally "red"-emitting SiNCs. Here, we obtained a different result. We show that the treatment of "red" emitting, already oxidized SiNCs in a water-based environment containing air-related radicals including nitrogen-containing species as well as oxygen, diminishes, rather than induces the "blue" luminescence.

Use of non-thermal plasma pre-treatment to enhance antibiotic action against mature Pseudomonas aeruginosa biofilms.

Non-thermal plasma (NTP), generated at atmospheric pressure by DC cometary discharge with a metallic grid, and antibiotics (gentamicin-GTM, ceftazidime-CFZ and polymyxin B-PMB), either alone or in combination, were used to eradicate the mature biofilm of Pseudomonas aeruginosa formed on Ti-6Al-4V alloy. Our aim was to find the conditions for NTP pre-treatment capable of enhancing the action of the antibiotics and thus reducing their effective concentrations. The NTP treatment increased the efficacy of relatively low concentrations of antibiotics. Generally, the highest effect was achieved with GTM, which was able to suppress the metabolic activity of pre-formed P. aeruginosa biofilms in the concentration range of 4-9 mg/L by up to 99%. In addition, an apparent decrease of biofilm-covered area was confirmed after combined NTP treatment and GTM action by SYTO®13 staining using fluorescence microscopy. Scanning electron microscopy confirmed a complete eradication of P. aeruginosa ATCC 15442 mature biofilm from Ti-6Al-4V alloy when using 0.25 h NTP treatment and subsequent treatment by 8.5 mg/L GTM. Therefore, NTP may be used as a suitable antibiofilm agent in combination with antibiotics for the treatment of biofilm-associated infections caused by this pathogen.

Modeling of concentric pattern of Serratia marcescens colony.

Serratia marcescens forms different colony patterns under distinct conditions. One of them is the concentric fountain-shaped pattern with pigmented center followed by unpigmented ring and pigmented rim. In this work, we study this pattern formation by construction of the mathematical model able to display this pattern based on putative metabolical traits, supported by series of experiments and by references. A pattern formation of such colony type depends on the disposition of glucose and amino acids, and is accompanied by a pH change in the agar medium. In this paper, we confirm that a metabolic activity of growing colony alters its environment which subsequently changes the colony formation. Presented model corresponds well with the real colony behaviour.

Medically important biofilms and non-thermal plasma.

In recent decades, the non-thermal plasma, i.e. partially or completely ionized gas produced by electric discharges at ambient temperature, has become of interest for its microbiocidal properties with potential of use in the food industry or medicine. Recently, this interest focuses not only on the planktonic forms of microorganisms but also on their biofilms. The works in this interdisciplinary field are summarized in this review. The wide range of biofilm-plasma interactions is divided into studies of general plasma action on bacteria, on biofilm and on its oral and dental application; a short overview of plasma instrumentation is also included. In addition, not only biofilm combating but also an important area of biofilm prevention is discussed. Various DC discharges of the point-to-plane type. Author's photograph, published in Khun et al. (Plasma Sources Sci Technol 27:065002, 2018).

Inactivation of dermatophyte infection by nonthermal plasma on animal model.

Superficial fungal infections are a major epidemiological issue with increasing prevalence and are a common global problem. This article describes experimental therapy of superficial fungal skin infection using low-temperature plasma. Groups of guinea pigs were artificially infected with Trichophyton mentagrophytes SK 3286 dermatophyte and treated with plasma produced by a DC cometary discharge with an inserted grid. The course of infection was a week shorter and milder in animals treated by plasma than that in nontreated animals, the significant lowering of dermatophytic germs also occurred in the treated group. The exposure to plasma causes no harm to experimental animals. The results allow for the development of a new dermatophytoses therapy by low temperature plasma treatment.

The fitness change and the diversity maintenance in the growing mixed colony of two Serratia rubidaea clones.

We extend the palette of possible colonies models of two different clones of Serratia rubidaea. Our model fits the real morphology of the colonies. We also present that the colony growth leads to a change in the ratio of the fitness which propose to be caused by the production of some signal. This signal influences the behavior of the clones and leads to the prolonged diversity maintenance. The explanation of the diversity maintenance of the mixed concurrent population in one niche is the current studied problem in the ecology and evolution.

Treatment of a superficial mycosis by low-temperature plasma: a case report.

A case of dermatomycosis caused by zoophilic strain of Trichophyton interdigitale was treated by low-temperature plasma produced by direct current (DC) cometary discharge. The shortening of skin lesion persistence along with suppression of subjective discomfort and etiological agent was observed.

Exploring Non-Thermal Plasma and UV Radiation as Biofilm Control Strategies against Foodborne Filamentous Fungal Contaminants.

In recent years, non-thermal plasma (NTP) has emerged as a promising tool for decontamination and disinfection within the food industry. Given the increasing resistance of microbial biofilms to conventional disinfectants and their adverse environmental effects, this method has significant potential for eliminating biofilm formation or mitigating the metabolic activity of grown biofilms. A comparative study was conducted evaluating the efficacy of UV radiation and NTP in eradicating mature biofilms of four common foodborne filamentous fungal contaminants: Alternaria alternata, Aspergillus niger, Fusarium culmorum, and Fusarium graminearum. The findings reveal that while UV radiation exhibits variable efficacy depending on the duration of exposure and fungal species, NTP induces substantial morphological alterations in biofilms, disrupting hyphae, and reducing extracellular polymeric substance production, particularly in A. alternata and F. culmorum. Notably, scanning electron microscopy analysis demonstrates significant disruption of the hyphae in NTP-treated biofilms, indicating its ability to penetrate the biofilm matrix, which is a promising outcome for biofilm eradication strategies. The use of NTP could offer a more environmentally friendly and potentially more effective alternative to traditional disinfection methods.

Overcoming antibiotic resistance: non-thermal plasma and antibiotics combination inhibits important pathogens.

Antibiotic resistance (ATBR) is increasing every year as the overuse of antibiotics (ATBs) and the lack of newly emerging antimicrobial agents lead to an efficient pathogen escape from ATBs action. This trend is alarming and the World Health Organization warned in 2021 that ATBR could become the leading cause of death worldwide by 2050. The development of novel ATBs is not fast enough considering the situation, and alternative strategies are therefore urgently required. One such alternative may be the use of non-thermal plasma (NTP), a well-established antimicrobial agent actively used in a growing number of medical fields. Despite its efficiency, NTP alone is not always sufficient to completely eliminate pathogens. However, NTP combined with ATBs is more potent and evidence has been emerging over the last few years proving this is a robust and highly effective strategy to fight resistant pathogens. This minireview summarizes experimental research addressing the potential of the NTP-ATBs combination, particularly for inhibiting planktonic and biofilm growth and treating infections in mouse models caused by methicillin-resistant Staphylococcus aureus or Pseudomonas aeruginosa. The published studies highlight this combination as a promising solution to emerging ATBR, and further research is therefore highly desirable.

Comparative assessment of UV-C radiation and non-thermal plasma for inactivation of foodborne fungal spores suspension in vitro.

Fungal contamination poses a persistent challenge to industries, particularly in food, healthcare, and clinical sectors, due to the remarkable resilience of fungi in withstanding conventional control methods. In this context, our research delves into the comparative efficacy of UV radiation and non-thermal plasma (NTP) on key foodborne fungal contaminants - Alternaria alternata, Aspergillus niger, Fusarium culmorum, and Fusarium graminearum. The study examined the impact of varying doses of UV radiation on the asexual spores of all mentioned fungal strains. Simultaneously, the study compared the effects of UV radiation and NTP on the metabolic activity of cells after spore germination and their subsequent germination ability. The results revealed that UV-C radiation (254 nm) did not significantly suppress the metabolic activity of cells after spore germination. In contrast, NTP exhibited almost 100% effectiveness on both selected spores and their subsequent germination, except for A. niger. In the case of A. niger, the effectiveness of UV-C and NTP was nearly comparable, showing only a 35% decrease in metabolic activity after 48 hours of germination, while the other strains (A. alternata, F. culmorum, F. graminearum) exhibited a reduction of more than 95%. SEM images illustrate the morphological changes in structure of all tested spores after both treatments. This study addresses a crucial gap in existing literature, offering insights into the adaptation possibilities of treated cells and emphasizing the importance of considering exposure duration and nutrient conditions (introduction of fresh medium). The results highlighted the promising antimicrobial potential of NTP, especially for filamentous fungi, paving the way for enhanced sanitation processes with diverse applications.

Silver nanoparticles with plasma-polymerized hexamethyldisiloxane coating on 3D printed substrates are non-cytotoxic and effective against respiratory pathogens.

Due to the emerging resistance of microorganisms and viruses to conventional treatments, the importance of self-disinfecting materials is highly increasing. Such materials could be silver or its nanoparticles (AgNPs), both of which have been studied for their antimicrobial effect. In this study, we compared the biological effects of AgNP coatings with and without a plasma-polymerized hexamethyldisiloxane (ppHMDSO) protective film to smooth silver or copper coatings under three ambient conditions that mimic their potential medical use (dry or wet environments and an environment simulating the human body). The coatings were deposited on 3D printed polylactic acid substrates by DC magnetron sputtering, and their surface morphology was visualized using scanning electron microscopy. Cytotoxicity of the samples was evaluated using human lung epithelial cells A549. Furthermore, antibacterial activity was determined against the Gram-negative pathogenic bacterium Pseudomonas aeruginosa PAO1 and antiviral activity was assessed using human rhinovirus species A/type 2. The obtained results showed that overcoating of AgNPs with ppHMDSO creates the material with antibacterial and antiviral activity and at the same time without a cytotoxic effect for the surrounding tissue cells. These findings suggest that the production of 3D printed substrates coated with a layer of AgNPs-ppHMDSO could have potential applications in the medical field as functional materials.

Comparison of the Effect of Plasma-Activated Water and Artificially Prepared Plasma-Activated Water on Wheat Grain Properties.

Recently, much attention has been paid to the use of low-temperature plasmas and plasma-activated water (PAW) in various areas of biological research. In addition to its use in medicine, especially for low-temperature disinfection and sterilization, a number of works using plasma in various fields of agriculture have already appeared. While direct plasma action involves the effects of many highly reactive species with short lifetimes, the use of PAW involves the action of only long-lived particles. A number of articles have shown that the main stable components of PAW are H2O2, O3, HNO2, and HNO3. If so, then it would be faster and much more practical to artificially prepare PAW by directly mixing these chemicals in a given ratio. In this article, we review the literature describing the composition and properties of PAW prepared by various methods. We also draw attention to an otherwise rather neglected fact, that there are no significant differences between the action of PAW and artificially prepared PAW. The effect of PAW on the properties of wheat grains (Triticum aestivum L.) was determined. PAW exposure increased germination, shoot length, and fresh and dry shoot weight. The root length and R/S length, i.e., the ratio between the underground (R) and aboveground (S) length of the wheat seedlings, slightly decreased, while the other parameters changed only irregularly or not at all. Grains artificially inoculated with Escherichia coli were significantly decontaminated after only one hour of exposure to PAW, while Saccharomyces cerevisiae decontamination required soaking for 24 h. The differences between the PAW prepared by plasma treatment and the PAW prepared by artificially mixing the active ingredients, i.e., nitric acid and hydrogen peroxide, proved to be inconsistent and statistically insignificant. Therefore, it may be sufficient for further research to focus only on the effects of artificial PAW.

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.

Decontamination of High-Efficiency Mask Filters From Respiratory Pathogens Including SARS-CoV-2 by Non-thermal Plasma.

The current pandemic resulted in a rapidly increasing demand for personal protective equipment (PPE) initially leading to severe shortages of these items. Hence, during an unexpected and fast virus spread, the possibility of reusing highly efficient protective equipment could provide a viable solution for keeping both healthcare professionals and the general public equipped and protected. This requires an efficient decontamination technique that preserves functionality of the sensitive materials used for PPE production. Non-thermal plasma (NTP) is a decontamination technique with documented efficiency against select bacterial and fungal pathogens combined with low damage to exposed materials. We have investigated NTP for decontamination of high-efficiency P3 R filters from viral respiratory pathogens in comparison to other commonly used techniques. We show that NTP treatment completely inactivates SARS-CoV-2 and three other common human respiratory viruses including Influenza A, Rhinovirus and Adenovirus, revealing an efficiency comparable to 90°C dry heat or UVC light. Unlike some of the tested techniques (e.g., autoclaving), NTP neither influenced the filtering efficiency nor the microstructure of the filter. We demonstrate that NTP is a powerful and economic technology for efficient decontamination of protective filters and other sensitive materials from different respiratory pathogens.

A Review of Microbial Decontamination of Cereals by Non-Thermal Plasma.

Cereals, an important food for humans and animals, may carry microbial contamination undesirable to the consumer or to the next generation of plants. Currently, non-thermal plasma (NTP) is often considered a new and safe microbicidal agent without or with very low adverse side effects. NTP is a partially or fully ionized gas at room temperature, typically generated by various electric discharges and rich in reactive particles. This review summarizes the effects of NTP on various types of cereals and products. NTP has undisputed beneficial effects with high potential for future practical use in decontamination and disinfection.

Inactivation of Acanthamoeba Cysts in Suspension and on Contaminated Contact Lenses Using Non-Thermal Plasma.

Water suspensions of cysts of a pathogenic clinical isolate of Acanthamoeba sp. were prepared, and the cysts were inactivated either in suspension or placed on the surface of contact lenses by the non-thermal plasma produced by the DC corona transient spark discharge. The efficacy of this treatment was determined by cultivation and the presence of vegetative trophozoites indicating non-inactivated cysts. The negative discharge appeared to be more effective than the positive one. The complete inactivation occurred in water suspension after 40 min and on contaminated lenses after 50 min of plasma exposure. The properties of lenses seem to not be affected by plasma exposure; that is, their optical power, diameter, curvature, water content and infrared and Raman spectra remain unchanged.

Effects of Non-Thermal Plasma Treatment on Seed Germination and Early Growth of Leguminous Plants-A Review.

The legumes (Fabaceae family) are the second most important agricultural crop, both in terms of harvested area and total production. They are an important source of vegetable proteins and oils for human consumption. Non-thermal plasma (NTP) treatment is a new and effective method in surface microbial inactivation and seed stimulation useable in the agricultural and food industries. This review summarizes current information about characteristics of legume seeds and adult plants after NTP treatment in relation to the seed germination and seedling initial growth, surface microbial decontamination, seed wettability and metabolic activity in different plant growth stages. The information about 19 plant species in relation to the NTP treatment is summarized. Some important plant species as soybean (Glycine max), bean (Phaseolus vulgaris), mung bean (Vigna radiata), black gram (V. mungo), pea (Pisum sativum), lentil (Lens culinaris), peanut (Arachis hypogaea), alfalfa (Medicago sativa), and chickpea (Cicer aruetinum) are discussed. Likevise, some less common plant species i.g. blue lupine (Lupinus angustifolius), Egyptian clover (Trifolium alexandrinum), fenugreek (Trigonella foenum-graecum), and mimosa (Mimosa pudica, M. caesalpiniafolia) are mentioned too. Possible promising trends in the use of plasma as a seed pre-packaging technique, a reduction in phytotoxic diseases transmitted by seeds and the effect on reducing dormancy of hard seeds are also pointed out.

Non-thermal Plasma Treatment of ESKAPE Pathogens: A Review.

The acronym ESKAPE refers to a group of bacteria consisting of Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. They are important in human medicine as pathogens that show increasing resistance to commonly used antibiotics; thus, the search for new effective bactericidal agents is still topical. One of the possible alternatives is the use of non-thermal plasma (NTP), a partially ionized gas with the energy stored particularly in the free electrons, which has antimicrobial and anti-biofilm effects. Its mechanism of action includes the formation of pores in the bacterial membranes; therefore, resistance toward it is not developed. This paper focuses on the current overview of literature describing the use of NTP as a new promising tool against ESKAPE bacteria, both in planktonic and biofilm forms. Thus, it points to the fact that NTP treatment can be used for the decontamination of different types of liquids, medical materials, and devices or even surfaces used in various industries. In summary, the use of diverse experimental setups leads to very different efficiencies in inactivation. However, Gram-positive bacteria appear less susceptible compared to Gram-negative ones, in general.