Lethal activity of nonthermal plasma sterilization against microorganisms

OBJECTIVE. To determine the range and the mode of germicidal activity of sterilants generated by a nonthermal plasma sterilization system for microorganisms. METHODS. Representative bacteria, spores, viruses, bacteriophages, and fungi were exposed to the plasma cycle and the residual viability was measured in vitro. To assess the mode of lethal injury, Escherichia coli, Staphylococcus aureus, Bacillus atrophaeus, and bacteriophages were exposed to the plasma cycle, and the effects of the plasma-generated sterilants on the biological parameters were determined. RESULTS. There were at least 4-6 log reductions in viability for all microorganisms after 10 minutes of exposure to the plasma cycle. Electron micrographs and studies of the inhibition of bacteriophage infectivity suggested that the primary injury is to the organisms' cell envelopes. The plasma cycle also denatured isolated bacterial proteins and inactivated bacteriophages, but it had no effect on isolated DNA and bacterial proteins within exposed bacteria. CONCLUSION. Nonthermal plasma, which is produced at atmospheric temperature and pressure, generates sterilants that kill high concentrations of microorganisms and inactivate viruses during a 10-minute exposure. The primary injury appears to be at the surface structures of the organisms. This suggests that nonthermal plasma has utility for sterilization of heat-sensitive medical materials and devices.