Cold atmospheric pressure plasma (CAP) offers a variety of therapeutic possibilities and induces the formation of reactive chemical species associated with oxidative stress. Mesenchymal stem/stromal cells (MSCs) play a central role in tissue regeneration, partly because of their antioxidant properties and ability to migrate into regenerating areas. During the therapeutic application, MSCs are directly exposed to the reactive species of CAP. Therefore, the investigation of CAP-induced effects on MSCs is essential. In this study, we quantified the amount of ROS due to the CAP activation of the culture medium. In addition, cell number, metabolic activity, stress signals, and migration were analyzed after the treatment of MSCs with a CAP-activated medium. CAP-activated media induced a significant increase in ROS but did not cause cytotoxic effects on MSCs when the treatment was singular and short-term (one day). This single treatment led to increased cell migration, an essential process in wound healing. In parallel, there was an increase in various cell stress proteins, indicating an adaptation to oxidative stress. Repeated treatments with the CAP-activated medium impaired the viability of the MSCs. The results shown here provide information on the influence of treatment frequency and intensity, which could be necessary for the therapeutic application of CAP.

Foodborne illness caused by bacterial pathogens is a global health concern and results in millions of infections annually. Therefore, food products typically undergo several processing stages, including sanitation steps, before being distributed in an attempt to remove pathogens. However, many sanitation methods have compounding effects on the color, texture, flavor, and nutritional quality of the product or do not effectively reduce the pathogens that food can be exposed to. Some bacterial pathogens particularly possess traits and tactics that make them even more difficult to mitigate such as biofilm formation. Non-thermal plasma sanitation techniques, including plasma-treated water (PTW), have proven to be promising methods that significantly reduce pathogenic bacteria that food is exposed to. Published work reveals that PTW can effectively mitigate both gram-positive and gram-negative bacterial biofilms. This study presents a novel analysis of the differences in antimicrobial effects of PTW treatment between biofilm-forming gram-positive bacteria, commonly associated with foodborne illness, that are sporulating (Bacillus cereus) and non-sporulating (Listeria monocytogenes). After treatment with PTW, the results suggest the following hypotheses: (1) that the non-sporulating species experiences less membrane damage but a greater reduction in metabolic activity, leading to a possible viable but non-culturable (VBNC) state, and (2) that the sporulating species undergoes spore formation, which may subsequently convert into vegetative cells over time. PTW treatment on gram-positive bacterial biofilms that persist in food processing environments proves to be effective in reducing the proliferating abilities of the bacteria. However, the variance in PTW’s effects on metabolic activity and cell vitality between sporulating and non-sporulating species suggest that other survival tactics might be induced. This analysis further informs the application of PTW in food processing as an effective sanitation method.

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Plasma-treated water (PTW) recently entered science as a sanitizing agent, which possess the capability for on-demand production. It offers interesting possibilities for sustainable and resource-saving applications in healthcare and food production. The present study monitors the impact of PTW on suspended cells before the biofilm formation of the putrefactive bacterium B. subtilis. Light and electron microscope imaging captures the maturing of growing biofilms within the first 24 h. Microbiological assays (proliferation, LIVE/DEAD, and XTT), which mirror the proliferation of the bacterium, the metabolic activity, and the integrity of the cell membrane, underpinning the metabolic response of still-suspended cells. B. subtilis cells without any treatment build up a resistive biofilm within the 24 h. Cells that remain in the supernatant predominantly appear as monomers or dimers. Treated B. subtilis cells have hampered biofilm formation and were not able to build up a confluent growing biofilm within the first 24 h. Moreover, the microscopic observation of PTW-treated suspension showed cellular aggregates with an unusually high connectivity of the individual cells. The findings suggest this cellular reaction as a counter measure against the adverse impact of PTW treatment. The experiments show the adverse impact of PTW on B. subtilis–biofilm formation and the phenomenological reaction of B. subtilis.

Foodborne pathogens such as E. coli, B. cereus, L. monocytogenes, and S. aureus cause many illnesses in Europe each year due to traits like biofilm formation, spore production, and high resistance to harsh conditions. This study investigated plasma-treated water (PTW) as an eco-friendly antimicrobial approach and examined its effect on bacterial growth curves to improve food safety. PTW was generated using a microwave plasma source, then applied to bacterial cultures that were monitored by optical density and colony counts. The bacterial growth was described by application of a logistic growth model to the optical density and colony count data. Results show that PTW mainly prolonged the lag phase of growth, with a stronger effect on Gram-positive bacteria than on Gram-negative bacteria. Although PTW initially reduced viable cell numbers, most bacteria eventually recovered and reached the stationary phase after a delay of about 2 to 11 h depending on the species. These effects may be due to cell damage, cell death, viable but nonculturable state induction, or stress responses such as spore formation. Further studies are needed to confirm how PTW performs in real food systems and biofilm settings.