Division of Environmental Physics -
Students Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava
Michal PELACH alumni student
MSc. study 2009 - 2011
Supervisor: Zdenko Machala Title: Comparison of direct and indirect effects of cold air plasma on bacteria contaminated surfaces Abstract: Experimental work concerning non-thermal air plasma treatment of gram-negative bacteria Salmonella typhimurium on agar surfaces is presented here comparing direct and indirect exposition to the plasma for various times (5-15 s). The results are characterized by visible differences of inactivated areas between these two methods of treatment. Bacteria inactivation with non-thermal atmospheric pressure plasma in the air is a highly complex process including many possible stress agents, such as charged particles, reactive neutral particles, UV and electromagnetic radiation and heat. In recent years, the most discussed agents mainly contributing to efficiency of plasma induced bio-decontamination, are charged particles and reactive neutral species In our work, bacteria contaminated agar surfaces are treated by non-thermal atmospheric pressure air plasma, induced by DC driven electrical discharges. The aim of prepared experimental setup was to compare direct and indirect exposition of the agar surface on Petri dishes to the discharge. This was especially set to separate reactive neutral particles and charged particles from the plasma. Our biological sample Salmonella typhimurium was prepared by cultivation in liquid nutrient broth and then spread onto a solid agar over the whole surface in Petri dishes. Samples were than directly or indirectly treated with plasma and incubated for 12 h. In indirect exposition only neutral reactive particles were able to reach the agar surface. In both exposition methods, we tried to ensure same electrical parameters. The results show, that direct exposition has stronger effect than indirect. However for longer times of exposure (15 s), the effect of the indirect exposition is comparable with the direct exposition. This indicates that neutral reactive species generated in our discharge are important in bacterial inactivation. We also showed that bacterial population continuously changes in time what is affecting the size of inactivated area.