Cold atmospheric pressure plasma inactivation of dairy associated planktonic cells of Listeria monocytogenes and Staphylococcus aureus

Abstract

The effect of cold atmospheric pressure plasma (CAPP) on three strains of Staphylococcus aureus and one strain of Listeria monocytogenes on gel discs was studied. A plasma jet operating in argon was used and exposure times were from 5 to 120 s. Bacteria had been isolated from dairy environments. In comparison, peracetic acid (PAA, 0.5% v/v) applied on cell suspensions at the same treatment times was studied. The cell viability was measured by flow cytometry and the culturable cells were determined by plate count technique. PAA reduced nearly 7 log cycles of both microorganisms after a short time (10 s). Concurrently, membrane permeabilization, RNA and DNA damage, and lack of esterase activity could be demonstrated. CAPP showed a mild biocidal effect with a maximum reduction of 1–2 log cycle after 120 s, and no significant impact on membrane permeabilization, RNA and DNA damage, or esterase activity. Therefore, for the selected processing parameters, PAA remains as more effective treatment in terms of inactivating pathogenic bacteria in dairy environments, reaching ~7 log cycles reductions. Further studies should determine the effect of higher CAPP exposure times on S. aureus and L. monocytogenes strains.