Inactivation of microorganisms by plasma of a positive (PC) and negative corona (NC) discharge in air at atmospheric pressure was investigated. Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Pseudomonas aeruginosa were chosen for the discharge inactivation. PC and NC produce three types of bactericidal agents, which are ultraviolet radiation (UV), neutral reactive species (R), and electric field and charged particles (E), respectively. We elucidated the contribution of each bioactive agent to the inactivation of S. aureus and P. aeruginosa. The influence of the charged particles in PC and NC on the cell inactivation is caused by different electrophysical effects, which lead nevertheless to an identical consequence: the cell membrane becomes more transparent for neutral reactive species. It gives additional possibility for neutral reactive species to increase the inactivation of cell by biochemical mechanisms. Due to that, total UV þ R þ E bactericidal effect in PC and NC is approximately the same and great -only a few tens of seconds is enough to inactivate completely S. aureus and P. aeruginosa cells.

Non-thermal plasma (NTP) consists of a huge amount of biologically active particles, whereas its temperature is close to ambient. This combination allows one to use NTP as a perspective tool for solving different biomedical tasks, including antitumor therapy. The treatment of tumor cells with NTP caused dose-dependent effects, such as growth arrest and apoptosis. However, while the outcome of NTP treatment has been established, the molecular mechanisms of the interaction between NTP and eukaryotic cells have not been thoroughly studied thus far. In this work, the mechanisms and the type of death of human colon carcinoma HCT 116 cells upon application of non-thermal argon plasma were studied. The effect of NTP on the major stress-activated protein p53 was investigated. The results demonstrate that the viability of HCT116 cells upon plasma treatment is dependent on the functional p53 protein. NTP treatment caused an increase in the intracellular concentration of p53 and the induction of the p53-controlled regulon. The p53-dependent accumulation of active proapoptotic caspase-3 was shown in NTP-treated cells. The study was the first to demonstrate that treatment of human colon carcinoma cells with NTP results in p53-dependent apoptosis. The results obtained contribute to our understanding of the applicability of NTP in antitumor therapy.

Nonthermal plasmas (NTPs) represent a new class of sterilizing agents. A full set of NTP bioactive factors includes electric components (E, charged particles and electric field), neutral active particles (R), and UV. A specific construction of the direct current (DC) corona source was used that allowed dissection of NTP bioactive factors and quantitative evaluation of their individual and combined action on bacterial pathogens Pseudomonas aeruginosa and Staphylococcus aureus. 10 and 120 s were required for the positive and negative coronas, respectively, to kill 10 5 colony-forming units (CFU) P. aeruginosa. 10 s was required for both positive and negative coronas to kill 10 5 CFU S. aureus. For the positive corona, the bactericidal activity of components decreased as R+UV>E+UV>>UV and E+UV>R+UV>>UV for P. aeruginosa and S. aureus, respectively. For the negative corona, the bactericidal activity decreased as R+UV>>E+UV=UV=0 and R+UV>>E+UV>UV≈0 for P. aeruginosa and S. aureus, respectively. Despite low, if any, activity of electric components in the negative corona, the whole plasma effect was much higher than the effect of neutral particles and UV alone. The obtained results demonstrated that different combinations of bioactive plasma components exerted diverse species-specific bactericidal effects. It is synergy among plasma bioactive factors that supplies high bactericidal activity of NTP.

In general non-thermal plasma generates three main types of bio-active agents: UV radiation, charged particles and neutral species like radicals and metastables. A role of each agent in bio-inactivation of microorganisms still remains as the subject for discussion. To simplify situation, we used pin-toplane positive and negative DC coronas in ambient air as a source for generation of bio-active agents. These discharges at atmospheric pressure practically do not produce UV radiation but generate predominantly the charged particles and neutral active species. In the case of humid air the positive and negative charged particles are H 3 O + , NO + and OH -, O 2 -, O 3 -, O -, NO 3 -, CO 3 -for positive and negative corona respectively. As for bio-active neutral species they are O, O 2 (ά 1 ∆), O 3 , OH, HO 2 and HNO 2 , HNO 3 as well in small numbers. This study was aimed to evaluate an effect of corona discharge on viability of the pathogenic bacteria Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa (Gram-negative) seeded on nutritive agar and to evaluate a role of the charged particles and neutral active species in a total bactericidal effect. To split the effects of the charged particles and neutral species on the microorganisms, we have done the experiments with corona in the rest air and in airflow removing neutral active agents from the agar surface to be treated. Full inactivation of bacteria was observed over the whole agar surface for both Grampositives and Gram-negatives when the agar surface was exposed to the mixture of charged particles and neutral species for 5 minutes. The obtained results showed that both charged and neutral active particles contribute essentially to the whole bactericidal effect of both positive and negative corona discharge. The detailed information will be presented in this report at the conference.