In English

Cold Plasma in Medicine Combatting Bacterial Biofilms

Saga Huld Helgadóttir
Göteborg : Chalmers tekniska högskola, 2016. 47 s.
[Examensarbete på avancerad nivå]

Solid, liquid and gas are what is generally called the three states of matter. Plasma is an ionized gas, where ionization is obtained by applying energy in the form of heat or high electrical fields to the gas, and it is the fourth state of matter. Plasmas can be of equilibrium or non-equilibrium type. In a plasma in an equilibrium state, the ions and electrons are in thermodynamic equilibrium, resulting in high gas temperatures. Plasmas used in medicine and healthcare are in highly non-equilibrium state and have gas temperatures that are suitable for treatment of living tissue without, or with minimal, damage to surrounding healthy tissue. The field of cold plasma in medicine is growing quickly and the possibilities seem endless. For example, cold plasma has been shown to have potential to be effectively combined with chemotherapy in cancer treatment and to promote wound sterilization, blood coagulation, and cell proliferation in wound healing. The main active agents in cold plasma have been proposed to be reactive chemical species, ions and electrons, heat radiation, electromagnetic fields, UV radiation, and visible light. The combination of the produced agents in the cold plasma is dependent on a number of things, for example, the type of gas used, air or noble gases, the input energy, and the pulse frequency. However, the mechanisms of action of the active agents are not fully understood, and more work has to be done in order be able to establish cold plasma as a solid technique in the field of medicine. After a description of the physics of cold plasma, its efficacy on bacterial biofilms was tested experimentally. 48-hour biofilms of two gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, and two gram-positive bacteria, Bacillus subtilis and Staphylococcus epidermidis, were exposed to the cold plasma at fixed exposure distance of 15 mm for exposure times of 0, 5, 10, 15, 30, and 60 minutes. The inactivation of bacteria was evaluated quantitatively with colony forming units (CFU) counting and qualitatively with live/dead fluorescent staining, and scanning electron microscope (SEM) was used to examine the morphological changes of the bacteria. Significant decrease in the number of viable bacterial cells was observed for all the bacteria. For the gram-negative bacterium E. coli, almost 90% reduction was observed after only a 10-minute exposure, however a 100% reduction was not accomplished after exposures of up to one hour. For the other gram-negative bacterium, P. aeruginosa, a reduction over 90% was not accomplished until after a 60-minute exposure, where the reduction reached almost 100%. For the gram-positive bacterium S. epidermidis, only about 80% reduction was accomplished after a 60-minute exposure. However, for the other gram-positive bacterium, B. subtilis, almost a 100% reduction was accomplished after only 5 minutes of exposure. II The results obtained were not surprising. Even though results of gram-negative bacteria being more sensitive to a cold plasma exposure than gram positive ones have been published, there have also been publications of B. subtilis being very sensitive to cold plasma exposure. However, the time to reach a 90% reduction varies greatly in published results, indicating that results from cold plasma experiments are highly dependent on the device used each time. It can be concluded that further studies need to be conducted for a clearer view of the efficacy of cold plasma in biofilm inactivation.

Nyckelord: Atmospheric pressure, bacteria, cold plasma, discharge, medicine,



Publikationen registrerades 2016-07-06. Den ändrades senast 2016-07-06

CPL ID: 239057

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