• antibacterial effect;
  • cold atmospheric plasma;
  • non-thermal plasma;
  • surface microdischarges

The composition of the gas for the Surface Micro-Discharge (SMD) plasma system is changed by applying variety of binary mixtures with oxygen, nitrogen and argon. Gram-negative Escherichia coli and gram-positive Enterococcus mundtii bacteria strains are inoculated on agar and exposed to the plasma using different gas mixture ratios either with a fixed applied voltage or with a fixed dissipated power. No bacterial reduction is observed in the absence of oxygen. Higher bactericidal efficacy is observed with higher oxygen fraction in the gas composition for the plasma. A threshold of the oxygen fraction is found where the bacterial reduction does not change much. The strong correlation between the bactericidal efficacy and the ozone concentration measured by optical absorption spectroscopy suggests that ozone generated by the SMD plasma is the major agent for the bacterial inactivation under the investigated conditions.ppap201300173-gra-0001