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Plasma-activated water mist (PAWM) is obtained by the ignition of plasma within an air-vapor mixture. PAWM demonstrates significant antibacterial properties, decreasing loads of foodborne pathogens by a factor of 35.5 for Listeria monocytogenes, 166 for Salmonella Typhimurium, and 266 for Escherichia coli O157:H7 within 15 s. Bacterial biofilms have a similar species-dependant susceptibility. Biofilms of L. monocytogenes, Salmonella Typhimurium, and E. coli O157:H7 are destroyed by 44%, 77%, and 71%, respectively, after being treated for 2 min. Obtained results suggest importance of short-lived radicals, because PAWM condensate is not bactericidal. A new model of PAW generation as a cyclic process of oxidation reactive nitrogen species by reactive oxygen species, which occurs during effective bidirectional mass transfer between heavily humid air and water mist in plasma discharge, is presented.

Chronic infections are associated with the formation of non-attached biofilm-like aggregates. In vitro models of surface-attached biofilms do not always accurately mimic these processes. Here, we tested a new approach to create in vitro non-attached bacterial aggregates using the principle of magnetic levitation of biological objects placed into a magnetic field gradient. Bacteria grown under magnetic levitation conditions formed non-attached aggregates that were studied with CLSM and SEM and characterized quantitatively. Non-attached aggregates consisted of bacteria submerged into an extracellular matrix and demonstrated features characteristic of biofilms, such as polymeric matrix that binds Ruby Red and Congo red dyes, prerequisite of bacterial growth, and increased resistance to gentamicin. Three quantitative methods were explored to characterize strain-specific potential to form non-attached aggregates: geometric sizes, relative quantities of aggregated and free-swimming bacteria, and Congo red binding. A comparison of three E. coli strains demonstrated that the strain weakly forming non-attached aggregates differed from strains that formed aggregates based on all three parameters (p<0.05). Further, we characterized biofilm formation on plastic and agar surfaces by these strains and found that good biofilm formation ability does not necessarily indicate good non-attached aggregate formation ability, and vice versa. The model and quantitative methods can be applied for in vitro studies of non-attached aggregates and modeling bacterial behavior in chronic infections, as it is important to increase understanding of the role that non-attached bacterial aggregates play in the pathogenesis of chronic diseases. Importance paragraph An increasing amount of evidence indicates that chronic infections are associated with non-attached biofilm-like aggregates formed by pathogenic bacteria. These aggregates differ from biofilms because they form under low-shear conditions within the volume of biological fluids and they do not attach to surfaces. Here, we describe an in vitro model that provides non-attached aggregate formation within the liquid volume due to magnetic levitation. Using this model, we demonstrated that despite morphological and functional similarities of non-attached aggregates and biofilms, strains that exhibit good biofilm formation might exhibit poor non-attached aggregate formation, suggesting that mechanisms underlying the formation of biofilms and non-attached aggregates are not identical. The magnetic levitation approach can be useful for in vitro studies of non-attached aggregate formation and simulation of bacterial behavior in chronic infections.

Non-thermal plasma (NTP) consists of a huge amount of biologically active particles, whereas its temperature is close to ambient. This combination allows one to use NTP as a perspective tool for solving different biomedical tasks, including antitumor therapy. The treatment of tumor cells with NTP caused dose-dependent effects, such as growth arrest and apoptosis. However, while the outcome of NTP treatment has been established, the molecular mechanisms of the interaction between NTP and eukaryotic cells have not been thoroughly studied thus far. In this work, the mechanisms and the type of death of human colon carcinoma HCT 116 cells upon application of non-thermal argon plasma were studied. The effect of NTP on the major stress-activated protein p53 was investigated. The results demonstrate that the viability of HCT116 cells upon plasma treatment is dependent on the functional p53 protein. NTP treatment caused an increase in the intracellular concentration of p53 and the induction of the p53-controlled regulon. The p53-dependent accumulation of active proapoptotic caspase-3 was shown in NTP-treated cells. The study was the first to demonstrate that treatment of human colon carcinoma cells with NTP results in p53-dependent apoptosis. The results obtained contribute to our understanding of the applicability of NTP in antitumor therapy.

Bacterial motility provides the ability for bacterial dissemination and surface exploration, apart from a choice between surface colonisation and further motion. In this study, we characterised the movement trajectories of pathogenic and probiotic Escherichia coli strains (ATCC43890 and M17, respectively) at the landing stage (i.e., leaving the bulk and approaching the surface) and its correlation with adhesion patterns and efficiency. A poorly motile strain JM109 was used as a control. Using specially designed and manufactured microfluidic chambers, we found that the motion behaviour near surfaces drastically varied between the strains, correlating with adhesion patterns. We consider two bacterial strategies for effective surface colonisation: horizontal and vertical, based on the obtained results. The horizontal strategy demonstrated by the M17 strain is characterised by collective directed movements within the horizontal layer during a relatively long period and non-uniform adhesion patterns, suggesting co-dependence of bacteria in the course of adhesion. The vertical strategy demonstrated by the pathogenic ATCC43890 strain implies the individual movement of bacteria mainly in the vertical direction, a faster transition from bulk to near-surface swimming, and independent bacterial behaviour during adhesion, providing a uniform distribution over the surface.

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Hepatocyte growth factor (HGF) is central to liver regeneration. The Internalin B (InlB) protein is a virulence factor produced by the pathogenic bacterium Listeria monocytogenes. InlB is known to mimic HGF activity by interacting with the HGF receptor (HGFR) and activating HGFR‐controlled signaling pathways. We expressed and purified the HGFR‐binding InlB domain, InlB321/15, cloned from the fully virulent clinical L. monocytogenes strain. HGFR and Erk1/2 phosphorylation was determined using Western blotting. The capacity of InlB321/15 to bind HGFR was measured using microscale thermophoresis. Liver regeneration was studied in a model of 70% partial hepatectomy (70%PHx) in male Wistar rats. The nuclear grade parameters were quantified using manual (percentage of binuclear hepatocytes), automated (nuclear diameters), or combined (Ki67 proliferation index) scoring methods. Purified InlB321/15 stimulated HGFR and Erk1/2 phosphorylation and accelerated the proliferation of HepG2 cells. InlB321/15 bound HGFR with Kd = 7.4 ± 1.3 nM. InlB321/15 injected intravenously on the second, fourth, and sixth days after surgery recovered the liver mass and improved the nuclear grade parameters. Seven days post 70% PHx, the liver weight indexes were 2.9 and 2.0%, the hepatocyte proliferation indexes were 19.8 and 0.6%, and the percentages of binucleated hepatocytes were 6.7 and 4.0%, in the InlB321/15‐treated and control animals, respectively. Obtained data demonstrated that InlB321/15 improved hepatocyte proliferation and stimulated liver regeneration in animals with 70% hepatectomy.