engleski

Determination of high voltage gas phase plasma treatment on Listeria innocua ATCC 33092 cells. Are they really inactivated?

High voltage gas phase plasmas are new developing techniques used for food and water decontamination [1, 2]. Still, there is a main question are the microorganisms really inactivated after the treatment or just under the stress. In this study we have examined the influence of high voltage plasma generated in the bubbles (injected air or argon-applied flow of 5 L/min) on inactivation, cells recovery, cellular leakage, proteomic analyses and transmission electron microscopy (TEM) analyses of Listeria innocua ATCC 33092 samples. Bacterial solution (200 mL) was treated in a glass reactor with a point-to-plate electrode configuration (high voltage electrode was stainless steel medical needle). Frequency of 60, 90 and 120 Hz, conductivity of solution 100 µS/cm, positive polarity and time of 5 and 10 min were chosen in order to determine their influence on listed parameters. The results of this study have showed that with a longer treatment time inactivation was higher. Complete inactivation was observed at all three frequencies with the injection of argon. Cellular leakage was determined at the 260 nm for nucleic acids and 280 nm for protein leakage. Higher leakage of proteins was detected compared to nucleic acids leakage. TEM analyses have showed that after the treatment (injected argon, 90 Hz and 10 min) membrane permeabilization occurred but not a complete disruption, as cellular macromolecules (DNA, RNA, proteins) were clearly inside the membrane wall (Figure 1). This was a proof why complete recovery of treated samples occurred. Proteomic analyses by MALDI-TOF/TOF MS have indicated overexpressed oxidative stress proteins compared to untreated sample.

Cold plasma, Listeria innocua, inactivation, recovery

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