Utku K. Ercan

Nonthermal Dielectric-Barrier Discharge Plasma-Induced Inactivation Involves Oxidative DNA Damage and Membrane Lipid Peroxidation in Escherichia coli

ABSTRACT Oxidative stress leads to membrane lipid peroxidation, which yields products causing variable degrees of detrimental oxidative modifications in cells. Reactive oxygen species (ROS) are the key regulators in this process and induce lipid peroxidation in Escherichia coli. Application of nonthermal (cold) plasma is increasingly used for inactivation of surface contaminants. Recently, we reported a successful application of nonthermal plasma, using a floating-electrode dielectric-barrier discharge (FE-DBD) technique for rapid inactivation of bacterial contaminants in normal atmospheric air (S. G. Joshi et al., Am. J. Infect. Control 38:293-301, 2010). In the present report, we demonstrate that FE-DBD plasma-mediated inactivation involves membrane lipid peroxidation in E. coli. Dose-dependent ROS, such as singlet oxygen and hydrogen peroxide-like species generated during plasma-induced oxidative stress, were responsible for membrane lipid peroxidation, and ROS scavengers, such as α-tocopherol (vitamin E), were able to significantly inhibit the extent of lipid peroxidation and oxidative DNA damage. These findings indicate that this is a major mechanism involved in FE-DBD plasma-mediated inactivation of bacteria.

Antimicrobial efficacy and wound-healing property of a topical ointment containing nitric-oxide-loaded zeolites.

Topical delivery of nitric oxide (NO) through a wound dressing has the potential to reduce wound infections and improve healing of acute and chronic wounds. This study characterized the antibacterial efficacy of an ointment containing NO-loaded, zinc-exchanged zeolite A that releases NO upon contact with water. The release rate of NO from the ointment was measured using a chemiluminescence detection system. Minimum bactericidal concentration assays were performed using five common wound pathogens, including Gram-negative bacteria (Escherichia coli and Acinetobacter baumannii), Gram-positive bacteria (Staphylococcus epidermidis and meticillin-resistant Staphylococcus aureus) and a fungus (Candida albicans). The time dependence of antimicrobial activity was characterized by performing log-reduction assays at four time points after 1-8 h ointment exposure. The cytotoxicity of the ointment after 24 h was assessed using cultured 3T3 fibroblast cells. Minimum microbicidal concentrations (MMCs) for bacterial organisms (5×10(7) c.f.u.) ranged from 50 to 100 mg ointment (ml media)(-1); the MMC for C. albicans (5×10(4) c.f.u.) was 50 mg ointment (ml media)(-1). Five to eight log reductions in bacterial viability and three log reductions in fungal viability were observed after 8 h exposure to NO-zeolite ointment compared with untreated organisms. Fibroblasts remained viable after 24 h exposure to the same concentration of NO-zeolite ointment as was used in antimicrobial tests. In parallel studies, full-thickness cutaneous wounds on Zucker obese rats healed faster than wounds treated with a control ointment. These data indicate that ointment containing NO-loaded zeolites could potentially be used as a broad-spectrum antimicrobial wound-healing dressing.

Chemistry for Antimicrobial Properties of Water Treated With Non-Equilibrium Plasma

Water demonstrates antimicrobial properties after it is treated with room temperature non-thermal plasma. In this work, we have applied UV spectroscopy, Raman spectroscopy, Electron Spin Resonance, and Mass spectroscopy experiments to investigate chemical species in water treated with non-thermal plasma. We propose that HONOO may be the major species contributing to the antimicrobial effects of this solution. However, it is also possible that the antimicrobial effect is due to the combination of all the radicals and oxidants in the solution

Chemical Changes in Nonthermal Plasma-Treated N-Acetylcysteine (NAC) Solution and Their Contribution to Bacterial Inactivation.

In continuation of our previous reports on the broad-spectrum antimicrobial activity of atmospheric non-thermal dielectric barrier discharge (DBD) plasma treated N-Acetylcysteine (NAC) solution against planktonic and biofilm forms of different multidrug resistant microorganisms, we present here the chemical changes that mediate inactivation of Escherichia coli. In this study, the mechanism and products of the chemical reactions in plasma-treated NAC solution are shown. UV-visible spectrometry, FT-IR, NMR, and colorimetric assays were utilized for chemical characterization of plasma treated NAC solution. The characterization results were correlated with the antimicrobial assays using determined chemical species in solution in order to confirm the major species that are responsible for antimicrobial inactivation. Our results have revealed that plasma treatment of NAC solution creates predominantly reactive nitrogen species versus reactive oxygen species, and the generated peroxynitrite is responsible for significant bacterial inactivation.

Calcium binding-mediated sustained release of minocycline from hydrophilic multilayer coatings targeting infection and inflammation.

Infection and inflammation are common complications that seriously affect the functionality and longevity of implanted medical implants. Systemic administration of antibiotics and anti-inflammatory drugs often cannot achieve sufficient local concentration to be effective, and elicits serious side effects. Local delivery of therapeutics from drug-eluting coatings presents a promising solution. However, hydrophobic and thick coatings are commonly used to ensure sufficient drug loading and sustained release, which may limit tissue integration and tissue device communications. A calcium-mediated drug delivery mechanism was developed and characterized in this study. This novel mechanism allows controlled, sustained release of minocycline, an effective antibiotic and anti-inflammatory drug, from nanoscale thin hydrophilic polyelectrolyte multilayers for over 35 days at physiologically relevant concentrations. pH-responsive minocycline release was observed as the chelation between minocycline and Ca2+ is less stable at acidic pH, enabling ‘smart’ drug delivery in response to infection and/or inflammation-induced tissue acidosis. The release kinetics of minocycline can be controlled by varying initial loading, Ca2+ concentration, and Ca2+ incorporation into different layers, enabling facile development of implant coatings with versatile release kinetics. This drug delivery platform can potentially be used for releasing any drug that has high Ca2+ binding affinity, enabling its use in a variety of biomedical applications.

Effect of liquid modified by non-equilibrium atmospheric pressure plasmas on bacteria inactivation rates

Several studies compared two dielectric barrier discharge (DBD) plasma treatment regimes and their effect on viable bacteria inactivation e.g. [1, 2]. Significant difference was shown between direct and indirect treatments where plasma either contacts the surface being treated or does not. The sterilization efficiency drops by almost an order of magnitude when plasma is generated remotely (indirectly) [1, 2]. However, this effect was mostly found on uniform surfaces such as agarous gel. In wounds for example, bacteria can often “hide” in pores. Therefore in the case of plasma treatment of wounds and other complex surfaces, irregularities in surface topology prevent effective implementation of direct plasma treatment. In this case, plasma related inactivation effect is believed to be delivered by neutral active species produced by the discharge in liquids (e.g. water, blood, etc.) present at the wound site, i.e. so-called plasma “pharmacological” effect.

Escherichia coli cellular responses to exposure to atmospheric-pressure dielectric barrier discharge plasma-treated N-acetylcysteine solution

To understand the underlying cellular mechanisms during inactivation of Escherichia coli in response to antimicrobial solution of nonthermal plasma‐activated N‐acetylcysteine (NAC).

Plasma acid and its applications

Summary form only given. Non-thermal atmospheric pressure plasma applied to the surface of water can oxidize organic molecules in the solution and kill bacteria in it. Ozonation of water produce a solution that retains its oxidation potential for several minutes. We show that direct exposure of deionized water not only to ozone but to other neutral and charged species produced in plasma creates a strong oxidizer in this water which, for the lack of a better term, we can call plasma acid. Plasma acid can remain stable for much longer time than ozonated water and its oxidizing power may be linked to the significant lowering of its pH. We report experiments that demonstrate plasma acids stability. We also show that observed pH of as low as 2.0 cannot be completely accounted for by the production of nitric acid; and that the conjugate base derived from superoxide is at least partly responsible for both, lowering of the pH and increase in the oxidizing power of the solution. Existence of a stable oxidizer created using plasma treatment of pure water not only raises interesting scientific questions and possibilities, but is likely to find many applications in situations where “on the spot” plasma treatment may be difficult to achieve.