Sterilization of Streptococcus pyogenes by afterglow dielectric barrier discharge using O sub(2) and CO sub(2) working gases

Streptococcus pyogenes is a causative agent in wide range of human diseases. To inactivate S. pyogenes by the afterglow of a dielectric barrier discharge (DBD), we prepared suspensions of the cultured bacterium in liquid (with concentrations of OD sub(600 nm) = 0.25 McFarland standard) and solid (with 7.75 x 10 super(5) spread cells per surface plate) Luria-Bertini (LB) broth media. The influence of DBD exposure on S. pyogenes was evaluated at 5, 10, and 15 min by two methods: turbidimetry analysis (for liquid solution) and determination of the number of colony-forming units (for solid media). Bacterial survival was strongly dependent upon on the working gas used. For a cultured LB liquid solution, it reached (21 +/- 5)% and (70 +/- 8)% at an exposure time of 15 min with O sub(2) and CO sub(2) working gases, respectively. Bacterial cell growth on the surface of the LB plate was 1 colony and 270 colonies for O sub(2) and CO sub(2) gases, respectively. The results suggest that the DBD of O sub(2) gas could be efficient in the disinfection of S. pyogenes in liquid and surface cultured media. The processes could be attributed to ozone and the excited singlet state O sub(2)(a super(1) sub(g)) as the active chemical agents.