Nina Abramzon

Biofilm Destruction by RF High-Pressure Cold Plasma Jet

Biofilms are bacterial communities embedded in a glue-like matrix mostly composed of exopolysaccharides and a small amount of proteins and nucleic acids. Conventional disinfection and sterilization methods are often ineffective with the biofilms since microorganisms within the biofilm show different properties from those in free planktonic life. The use of the gas discharge plasmas is a novel alternative since the plasmas contain a mixture of charged particles, chemically reactive species, and UV radiation. The four-day-old single-species biofilms were produced using Chromobacterium violaceum, a gram-negative bacterium commonly present in soil and water. The gas discharge plasma was produced by using an Atomflo 250 reactor (Surfx Technologies), and the bacterial biofilms were exposed to it for different periods of time. Our results show that a 10-min plasma treatment is able to kill almost 100% of the cells. The results show a rapid initial decline in the colony forming units per milliliter (phase one) that is followed by a much slower subsequent decline (phase two) of the D-values that are longer than the inactivation of the planktonic organisms, suggesting a more complex inactivation mechanism for the biofilms. Two hypotheses are offered to explain this biphasic behavior. Optical emission spectroscopy was used to study the plasma composition, and the role of the active species is discussed. These results indicate the potential of plasma as an alternative way for biofilm removal

Is gas-discharge plasma a new solution to the old problem of biofilm inactivation?

Conventional disinfection and sterilization methods are often ineffective with biofilms, which are ubiquitous, hard-to-destroy microbial communities embedded in a matrix mostly composed of exopolysaccharides. The use of gas-discharge plasmas represents an alternative method, since plasmas contain a mixture of charged particles, chemically reactive species and UV radiation, whose decontamination potential for free-living, planktonic micro-organisms is well established. In this study, biofilms were produced using Chromobacterium violaceum, a Gram-negative bacterium present in soil and water and used in this study as a model organism. Biofilms were subjected to an atmospheric pressure plasma jet for different exposure times. Our results show that 99.6 % of culturable cells are inactivated after a 5 min treatment. The survivor curve shows double-slope kinetics with a rapid initial decline in c.f.u. ml(-1) followed by a much slower decline with D values that are longer than those for the inactivation of planktonic organisms, suggesting a more complex inactivation mechanism for biofilms. DNA and ATP determinations together with atomic force microscopy and fluorescence microscopy show that non-culturable cells are still alive after short plasma exposure times. These results indicate the potential of plasma for biofilm inactivation and suggest that cells go through a sequential set of physiological and morphological changes before inactivation.

Gas discharge plasmas are effective in inactivating Bacillus and Clostridium spores

Bacterial spores are the most resistant form of life and have been a major threat to public health and food safety. Nonthermal atmospheric gas discharge plasma is a novel sterilization method that leaves no chemical residue. In our study, a helium radio-frequency cold plasma jet was used to examine its sporicidal effect on selected strains of Bacillus and Clostridium. The species tested included Bacillus subtilis, Bacillus stearothermophilus, Clostridium sporogenes, Clostridium perfringens, Clostridium difficile, and Clostridium botulinum type A and type E. The plasmas were effective in inactivating selected Bacillus and Clostridia spores with D values (decimal reduction time) ranging from 2 to 8xa0min. Among all spores tested, C. botulinum type A and C. sporogenes were significantly more resistant to plasma inactivation than other species. Observations by phase contrast microscopy showed that B. subtilis spores were severely damaged by plasmas and the majority of the treated spores were unable to initiate the germination process. There was no detectable fragmentation of the DNA when the spores were treated for up to 20xa0min. The release of dipicolinic acid was observed almost immediately after the plasma treatment, indicating the spore envelope damage could occur quickly resulting in dipicolinic acid release and the reduction of spore resistance.

Plasma Interactions With Bacterial Biofilms as Visualized Through Atomic Force Microscopy

Bacterial biofilms are microbial communities that are less susceptible to standard killing methods than free-living bacteria. Gas-discharge plasmas were used to treat biofilms for various exposure times. After 5-min plasma exposure, 90% of culturable cells were removed. Atomic-force-microscope images that reveal the sequential changes in cell morphology occurring during plasma treatment are presented.

Kinetics and microscopic studies of plasma-assisted biofilm destruction

Summary form only given. Biofilms are microbial communities attached to either an inert or living surface and encased in an exopolysaccharidic matrix also including a small amount of proteins and nucleic acids. Bacteria aggregated in a biofilm behave in a different way compared to free, planktonic cells. In the former, there are cooperative interactions among cells, thus; conventional disinfection methods are often ineffective with biofilms. The use of gas discharge plasmas is a potential solution to this problem since plasmas contain a mixture of charged particles, chemically reactive species, and UV radiation, individually known as effective killing agents. We have previously reported the use of plasma to destroy bacterial biofilms. Four day old biofilms were produced using Chromobacterium violaceum, a gram negative bacterium commonly present in soil and water. Gas discharge plasma was produced by using an AtomfloTM 250 reactor (Surfx Technologies, CA). An atmospheric pressure plasma jet was generated by using He and N2 as a secondary gas. Biofilms were exposed to plasma for different periods of time, then disaggregated by sonication and processed to determine the kinetics of the killing process. For microscopy studies, biofilms underwent the same procedure and cells were examined using atomic force (AFM) and fluorescence microscopy. Optical emission spectroscopy was used to study plasma composition. Our results show that after a 10-minute plasma treatment, almost 100% of the viable cells are removed. The kinetics show a rapid initial decline in CFU/mL followed by a much slower subsequent decline with D-values that are longer than for the inactivation of planktonic organisms. Fluorescence microscopy and AFM confirmed these results and suggest that cells may undergo cell wall damage after plasma treatment. These results indicate the potential of plasma as an alternative way for biofilm removal

Biofilm destruction by he-O2 RF highpressure cold plasma jet

Summary form only given. Biofilms are populations of microorganisms set in a glue-like matrix mostly composed of exopolysaccharides and a small amount of proteins and nucleic acids. Biofilms play an important role in bacterial pathogenesis in humans, animals, and plants, and in bacterial attachments to surfaces such as in medical devices, dental waterlines, etc. Disinfection and sterilization methods frequently used for microorganisms in free, planktonic life are often ineffective on biofilms. Gas discharge plasmas, composed of a mixture of charged particles, chemically reactive species, and UV radiation are a novel sterilization alternative. The relationship between killing effectiveness and exposure time was studied for 4 day-old biofilm samples treated with an AtomfloTM 250 gas discharge plasma source (Surfx Technologies, CA) operating with He (at 20.4 L/min flow) and O2 (at 0.400 L/min). Biofilm samples are prepared using Chromobacterium violaceum, a gram negative bacterium commonly present in soil and water. Optical emission spectroscopy is used to study plasma composition and temperature which is then correlated with the killing effectiveness. In addition, the killing effectiveness of the He-O2 plasma is compared to that reported previously for He-N 2 plasma

Destruction of Bacterial Communities using Gas Discharge Plasma.

Summary form only given. Biofilms are microbial communities attached to an environmental surface and embedded in an extracellular glue-like matrix. Biofilms are involved in bacterial pathogenesis and attachment to surfaces such as pipes and medical devices. Microorganisms in biofilms show different properties compared to free-living cells; thus, conventional methods of killing bacteria are often ineffective with biofilms. Therefore, the ability to destroy these organisms is critical. The use of non-thermal plasmas potentially offers an effective alternative to conventional sterilization methods because plasmas contain a mixture of charged particles, chemically reactive species, and UV radiation and their decontamination potential relative to individual microorganisms is well established. However, to our knowledge, there is no information about the use of plasma to destroy bacterial biofilms. 4 and 7 day-old bacterial biofilms were produced using two bacterial species Rhizobium gallicum, Chromobaderium violaceum CV026 or a mixture of both bacteria. Gas discharge plasma was produced by using an AtomfloTM 250 reactor (Surfx Technologies, CA). An atmospheric pressure plasma was generated by using a He flow of 20.4 L/min and a secondary gas flow (N2) of 0.305 L/min. Bacterial biofilms were exposed to plasma for different exposure times. Our results show that a 10-minute plasma treatment was able to kill 100% of the cells in most cases. Optical emission spectroscopy was used to study plasma composition and temperature which was then correlated with the effectiveness of killing. An emission spectrum from 200-450 nm will be presented. The characteristic features of the spectrum in the far ultraviolet are the NO gamma-bands near 250 nm and an OH band around 309 nm. The most prominent emission is due to the N2 2nd positive band. Using the N2 emissions, a plasma rotational temperature of 325 K was obtained with a margin of uncertainty of 20 K