Sterilization of Streptococcus pyogenes by afterglow dielectric barrier discharge using O2 and CO2 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 OD600 nm = 0.25 McFarland standard) and solid (with 7.75 × 105 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 O2 and CO2 working gases, respectively. Bacterial cell growth on the surface of the LB plate was 1 colony and 270 colonies for O2 and CO2 gases, respectively. The results suggest that the DBD of O2 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 O2(a1Δg) as the active chemical agents.