New plasma medicine research shows its antibacterial effects, potential uses

A research group has found that direct low-temperature plasma (LTP) treatment and plasma-activated media are effective treatments against bacteria found in liquid cultures.

A research group has found that direct low-temperature plasma (LTP) treatment and plasma-activated media are effective treatments against bacteria found in liquid cultures. The team, consisting of researchers from Penn State's College of Engineering, College of Agricultural Sciences and College of Medicine, including engineers, physicists, veterinary and biomedical scientists and medical professionals, is using an atmospheric-pressure plasma jet to use room temperature -- "cold" -- plasma to treat bacteria.

The results of the study were published in the journal IEEE Transactions on Radiation and Plasma Medical Sciences. Plasma, the fourth state of matter, is typically very hot -- thousands to millions of degrees. By using plasma generated at atmospheric pressure or in liquids, the researchers can create molecules and atoms with antibacterial effects without burning anything.

Sean Knecht, assistant teaching professor of engineering design at Penn State and leader of the Cross-disciplinary Laboratory for Integrated Plasma Science and Engineering, said this process creates many different types of reactive particles, making the likelihood of bacterial mutations to simultaneously combat all the particles almost nonexistent. Knecht explained that the team's research results, published in Scientific Reports, show that plasma technology generates large amounts of reactive oxygen species or reactive particles created from molecules that contain oxygen atoms, including oxygen molecules in the air and water vapour.

"Over the course of four generations of bacteria, these bacteria do not acquire any form of resistance to the plasma treatment," he said. Girish Kirimanjeswara, associate professor of veterinary and biomedical sciences at Penn State, said this is extremely important due to the typical way bacteria mutate, making them resistant to antibiotics.

Antibiotics target a specific metabolic pathway, essential protein or nucleic acids in bacteria. Because of this, antibiotics have to enter a bacterial cell to find and bind to that specific target. Any bacterial mutation that decreases an antibiotic's entry capabilities or increases its rate of exit makes the antibiotic less effective. Mutations happen naturally at a low rate but can rapidly accumulate by selection pressure when introduced to antibiotics aimed at fighting the bacteria.

According to Kirimanjeswara, the team's research results show that plasma treatment produces various reactive oxygen species at a concentration high enough to kill bacteria, but low enough to not have negative impacts on human cells. He explained that the oxygen species quickly target virtually every part of the bacteria including proteins, lipids, and nucleic acids. The team also applied these findings to design a system that can create plasma directly in liquids. The researchers intend to create plasma in the blood to address cardiovascular infections directly at the source.

To do so, high electric voltage and large electric currents are typically used. In the plasma system created by the researchers, the electrical current and energy that might reach the patient are minimised by using dielectric, or electrically-insulating, materials. Materials that the team would typically use to create the plasma include glass and ceramic due to their capability to withstand high local temperatures. These materials tend to make the blood clot and may not be very flexible, a necessity if they are to be used in the cardiovascular system.

The team is investigating insulating coatings that are biocompatible, or acceptable by the human body, and flexible. Knecht said the team has identified a polymer called Parylene-C. The team is further pursuing this avenue, as polymers have low melting points and may not withstand repeated exposure to plasma. "Biocompatible polymers can be used for plasma generation in biological liquids, but their lifetime is limited," Knecht said.

"New unique plasma generation designs must be developed to produce lower intensity plasma discharges that can extend their lifetime. That is what we are continuing to work on," he added. (ANI)

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