G. Fridman

Control of methicillin-resistant Staphylococcus aureus in planktonic form and biofilms: A biocidal efficacy study of nonthermal dielectric-barrier discharge plasma

BACKGROUND Bacterial contamination of surfaces with methicillin-resistant Staphylococcus aureus (MRSA) is a serious problem in the hospital environment and is responsible for significant nosocomial infections. The pathogenic contaminants form biofilms, which are difficult to treat with routine biocides. Thus, a continuous search for novel disinfection methods is essential for effective infection control measures. This demonstration of a novel technique for the control of virulent pathogens in planktonic form as well as in established biofilms may provide a progressive alternative to standard methodology. METHODS We evaluated a novel technique of normal atmospheric nonthermal plasma known as floating-electrode dielectric-barrier discharge (FE-DBD) plasma against a control of planktonic and biofilm forms of Escherichia coli, S aureus, multidrug-resistant methicillin-resistant S aureus (MRSA) -95 (clinical isolate), -USA300, and -USA400, using widely accepted techniques such as colony count assay, LIVE/DEAD BacLight Bacterial Viability assay, and XTT (2,3-Bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay. RESULTS Exposure of free living planktonic forms of E coli, S aureus, and MRSA were rapidly inactivated by DBD plasma. Approximately 10(7) bacterial cells were completely (100%) killed, whereas 10(8) and 10(9) were reduced by approximately 90% to 95% and 40% to 45%, respectively, in less than 60 seconds (7.8 J/cm(2)) and completely disinfected in < or =120 seconds. In established biofilms, the susceptibility of MRSA USA400 was comparable with USA300 but less susceptible than MRSA95 (clinical isolate), S aureus, and E coli (P < .05) to FE-DBD plasma, and plasma was able to kill MRSA more than 60% within 15 seconds (1.95 J/cm(2)). The killing responses were plasma exposure-time dependent, and cell density dependent. The plasma was able disinfect surfaces in a less than 120 seconds. CONCLUSION Application of DBD plasma can be a valuable decontamination technique for the removal of planktonic and biofilm-embedded bacteria such as MRSA -USA 300, -USA 400, methicillin-sensitive S aureus (MSSA), and E coli, the more common hospital contaminants. Of interest, E coli was more resistant than S aureus phenotypes.

Biological responses of Bacillus stratosphericus to Floating Electrode-Dielectric Barrier Discharge Plasma Treatment

Aims:  Dielectric barrier discharge (DBD) plasma is used for sterilization of contaminated inanimate surfaces but seldomly optimized and depends upon the type of organisms and the plasma treatment duration, (net energy deposited) this efficacy varies. The proposed study was designed to see biological responses of one of the robust organism, Bacillus stratosphericus.

Applications of Non Thermal Atmospheric Pressure Plasma in Medicine

Non-thermal atmospheric pressure plasma is now being developed for use in various medical applications. Over the past few years a lot of clinical applications of non-thermal plasma have been tested and the results show promising potential for Plasma Medicine. In this paper we present a review of various applications of non-thermal plasma in medicine like non-thermal plasma assisted blood coagulation and skin sterilization, melanoma skin cancer treatment and treatment of cornea lesions.

Effect of Dielectric Barrier Discharge Treatment of Blood Plasma to Improve Rheological Properties of Blood

The whole blood viscosity (WBV) is one of the major independent indicators for the risk of cardiovascular disease, stroke, and peripheral arterial diseases. Furthermore, oxidized LDL molecules are known to cause atherosclerotic plaques in arteries, and it is one of the key components that increase WBV. The present study attempted to reduce WBV by coagulating plasma proteins and lipid molecules from blood plasma using non-thermal dielectric barrier discharge (DBD) and removing them through filtration. The DBD treatment was found to produce coagulated particles in blood plasma. After filtration of the coagulated particles, WBV decreased by 9.1 and 17.7% for both systolic and diastolic blood viscosities, respectively. The present results suggest that the removal of excess plasma proteins and lipid molecules might be feasible using DBD treatment.

Uniform and Filamentary Nature of Continuous-Wave and Pulsed Dielectric Barrier Discharge Plasma

Observations of atmospheric pressure DBD plasma were conducted through the transparent electrode in Air, Argon, Helium, Nitrogen and Oxygen gasses at 1 and 3 standard liters per minute (s1pm) flow rates through the discharge gap, utilizing three types of excitation waveforms. Three phenomena were observed: (1) plasma filaments travel with the gas at the same speed as the gas for some but not all gases; (2) propagation of excitation is observed in Nitrogen plasma and the filament motion has no directional preference with gas flow direction; and (3) Oxygen, Nitrogen and Helium plasmas were observed to be rather uniform at least over longer time periods.

Sterilization of Living Human and Animal Tissue by Non-Thermal Atmospheric Pressure Dielectric Barrier Discharge Plasma

Summary form only given. Sterilization prior to a medical procedure (pre-operative), during, or following such a procedure has always been an issue at a hospital. Sterilization by liquid chemistry (alcohol, or Betadinetrade) has been available for a long time; however, such a procedure becomes difficult if not impossible when attempting to sterilize an open wound, a diabetic sore, or a burn site. Thus, controllable and targeted sterilization of living tissue without contact with or damage to this tissue is needed. Non-thermal atmospheric pressure plasmas have long been used in sterilization of various surfaces without damage to such surfaces and offer a good solution for skin sterilization as well. Presented is a method of sterilization of living tissue using a floating electrode dielectric barrier discharge (FF-DBD), based on a conventional DBD. Here plasma is bounded by quartz dielectric on one side and tissue of a living animal or human on the other side. Complete sterilization (> 7-log reduction in viable colony forming units) is shown from common bacteria abundant on human skin (Streptococcus staphylococcus, and yeast), and from model bacteria such as Escherichia coli, Bacillus subtilis spores, etc. Sterilization is normally achieved, depending on initial microorganism concentration, in 2 to 6 seconds of treatment (up to 15 seconds in some special cases), while no damage is observed during such treatment either visually or microscopically. Microscopic tissue damage assessment is carried out via tissue collection, sectioning, Haematoxylin and Eosin stain (H&E), and microscopic analysis. Mechanisms of this interaction and plasma selectivity to killing bacteria without damaging skin will be discussed. Data from a differential skin toxicity trial on SKIII hairless mice will be presented. During this trial, plasma doses are escalated until damage to animal skin is observed. Plasma-chemical effects are separated from thermal damage by use of FE-DBD plasma in non-thermal (microfilament temperature ~300 K +/-30 K) or thermal (~500-700 K) regimes. Non-thermal plasma regimes are shown to be less damaging while achieving nearly the same sterilization efficiency.

Self-Organization and Migration of Dielectric Barrier Discharge Filaments in Argon Gas Flow

Observations of atmospheric-pressure dielectric barrier discharge are conducted through a water-filled electrode in atmospheric-pressure argon gas flow. Quasi-symmetric self-organized discharge filaments were observed. The streamers moved with the gas flow, and the migration velocity increased with increasing gas velocity.

Toxicity of direct non-thermal atmospheric pressure plasma treatment of living tissue

Non-thermal atmospheric pressure dielectric barrier discharge plasma applied directly to living tissues is now being widely considered for various clinical applications. One of the key questions that arise in this type of topical treatment is if the skin remains undamaged after non-thermal plasma treatment.

Mechanisms of direct dielectric barrier discharge plasma inactivation of e. coli

Bacteria inactivation efficiency of direct atmospheric pressure dielectric barrier discharge treatment has been shown to be extremely strong [1], however mechanisms of DBD plasma sterilization is still unclear. We have performed a series of experiments which allow to understand bacteria inactivation effects of various active species generated in plasma, including charged particles, neutral short and long living species, and UV photons. Also, we have studied dependence of sterilization efficiency on gas composition and amount of free water which cover bacteria during DBD plasma treatment. The results of these model experiments allowed us to determine conditions in which best sterilization effect on surface of agar may be achieved: fast and effective bacteria inactivation by direct DBD plasma is shown to be related to presence of both positive and negative ions in combination with molecular oxygen and free water molecules and strongly depends on thickness of water layer on top of treated surface. Based on these experimental results we propose possible physical-chemical mechanism of DBD plasma bacteria inactivation.

Penetration of direct non-thermal plasma treatment into living cells

Here the possibility that effects of the plasma treatment can penetrate though cellular membranes without destroying them is studied. DNA double stranded breaks (DSBs) in human fibroblast cells were detected to assess effects of plasma treatment. Hydrogen peroxide treatment was used as a positive control as it is comparable to ionizing radiation. The results indicate that short direct plasma treatment at low power does produce DNA DSBs at the levels comparable to the positive control without permanent membrane damage.