Atmosferic pressure non-thermal plasma: Preliminary investigation

Antibacterial activity of atmosferic pressure non-thermal plasma (APNTP) was assessed for bacterial, yeast and mold strains. This investigation is to be considered preliminary: a second step is envisaged in which the efficacy of the technique and the device will be assessed directly on food of animal and plant origin. The strains (ATCC or wild type) of Listeria innocua, Escherichia coli, Salmonella thyphimurium, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, Proteus mirabilis (bacteria); Alternaria alternata, Aspergillus flavus, Cladosporium herbarum, Fusarium graminearum, Geotrichum candidum, Penicillium roqueforti, Rhizopus nigricans (moulds); Candida parapsilosis and Candida albicans (yeasts) were subjected to plasma plume generated by the action of electric fields with a gas mixture (oxygen and helium) delivered for 5 min at a distance of 2 cm. Types of experiments were listed as following: microorganism at concentration 1×10^8 and 1×10⁴ cfu on PCA (Plate Count Agar); Listeria innocua and Salmonella thiphymurium at concentration 1×10^4 cfu on semi-synthetic and synthetic medium; mycetes (moulds and yeasts) at concentration 1×10^8 and 1×10^4 cfu on SDA (Sabouraud Dextrose Agar). The results obtained on the bacteria subjected to atmospheric cold plasma were evident on all the strains tested except for Proteus mirabilis (1×10^8 cfu), most evident at a concentration of 1×10^4 cfu, not only on culture media PCA but also on semi-synthetic medium and jelly meat-PCA medium. In spite of bacterial results, treatment with plasma plume did not decrease or inhibit of fungal growth. That means plasma plume was neither fungicidal nor fungistatic activities.