Inactivation of bacterial endospores on surfaces by plasma processed air

In case of biological hazards and pandemics, personal protective equipment of rescue forces is currently manually decontaminated with harmful disinfectants, primarily peracetic acid. To overcome current drawbacks regarding supply, handling and disposal of chemicals, the use of plasma processed air (PPA) represents a promising alternative for surface decontamination on site. In this study, the sporicidal efficiency of a portable plasma system, designed for field applications, was evaluated.

The developed plasma device is based on a dielectric barrier discharge (DBD) and operated with ambient air as process gas. PPA from the plasma nozzle was flushed into a treatment chamber (volume: 300 l) and bacterial endospores (Bacillus subtilis and Bacillus atrophaeus) dried on different surfaces were treated under variable conditions. Reductions in spores by more than 4 log₁₀ were found within 3 min of PPA exposure. However, the presence of endospores in agglomerates or in an organic matrix as well as the complexity of the respective surface microstructure negatively affected the inactivation efficiency. When endospores were embedded in a dried protein matrix, mechanical wiping with swabs during exposure to PPA increased the inactivation effect significantly. Gaseous ozone alone did not provide a sporicidal effect. Significant spore inactivation was only obtained when water vapour was injected into the PPA stream.

The results show that endospores dried on surfaces can be reduced by several orders of magnitude within few minutes in a treatment chamber which is flushed with PPA from of a DBD plasma nozzle.

Plasma processed air generated on site by DBD plasma nozzles could be a suitable alternative for the disinfection of various surfaces in closed rooms.