Antimicrobial efficacy of non-thermal atmospheric pressure plasma jet on oral micro-organisms

Summary form only given. Non-thermal pressure atmospheric plasma jets are being intensively studied with respect to potential applications in medicine due to their advantage of avoiding harmful thermal damage on human body. Recent researches have revealed their several important applications as medical devices as the possible selective inactivation of bacteria, fungi, parasites and viruses in and on living tissue, without causing damage to human cell. However, despite of the many investigations, details of the mechanisms related to how non-thermal plasma has effects on bacteria are still largely unknown. Oral pathogens such as Streptococcus mutans (S.mutans) and Staphylococcus aureus (S.aureus) result in dental/oral cavity diseases, and numerous methods of removing such pathogens have been investigated. Hence the aim of this study was to investigate the antimicrobial efficacy of non-thermal atmospheric pressure plasma jet on oral micro-organisms, and suggest the method of investigating the underlying mechanisms. In this experiment, Streptococcus mutans (S.mutans), Staphylococcus aureus (S.aureus) from a primary stock culture were inoculated on an agar plate. After overnight incubation, a small sample of the colonies was smeared on an object slide using a medical swab. A suitable spot on the glass plate was then chosen to record the untreated bacteria with the atomic force microscope in tapping mode. Afterwards, the selected region was plasma treated for a defined period of time. To evaluate the antimicrobial property of non-thermal plasma, we investigated the colony forming unit of bacteria using atomic force microscopy (AFM) and agar plating method before and after plasma treatment at high resolution. The results indicated that the non-thermal atmospheric pressure plasma jet had effect on oral micro-organisms. Also, from the methodological point of view, the AFM has proved to be an attractive tool for the investigation of plasma in terms of colony forming units, w- ich could be applied in future studies for explanation of anti-microbial mechanisms of plasma.