Inactivation of vegetative bacteria in a liquid medium by gas plasma under atmospheric pressure

The bactericidal effect of gas plasma on vegetative bacteria, including Escherichia coli K12, Escherichia coli O157:H7, Salmonella typhimurium or Pseudomonas aeruginosa, in 0.9% (w/v) NaCl was investigated under atmospheric pressure. Circumambient air, which had 40% relative humidity (r.h.), was introduced into the plasma-generating unit at 71/min, and was excited by applying radio frequency discharge (20 kHz) to a conductive electrode in the unit. This caused the circumambient air to form atmospheric gas plasma (AGP). By exposing each cell suspension surface to the AGP, 10⁷CFU/ml of viable reduction was achieved within 15 min in all strains tested. Those survival curves showed a two-step process, a slow process followed by a much faster one. The bactericidal effect was not attributed to ozone. The AGP with circumambient air apparently increased the electrical conductivity in deionized water. It is concluded that ions from the AGP was responsible for the bactericidal effect.