The bactericidal effect of a positive and negative corona on Gram-positive and Gram-negative bacteria

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-to-plane 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 H₃O⁺, NO⁺ and OH^-, O₂^-, O₃^-, O^-, NO₃^-, CO₃^- for positive and negative corona respectively. As for bio-active neutral species they are O, O₂(ά¹Δ), O₃, OH, HO₂ and HNO₂, HNO₃ 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 Gram-positives 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 cor- na discharge. The detailed information will be presented in this report at the conference.