## 3 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Swimming**} & \multicolumn{3}{c}{**Swarming**} \\ \hline
**Time (h)** & **Ctrl** & **350 \(\mu\)L/mL** & **400 \(\mu\)L/mL** & **Ctrl** & **350 \(\mu\)L/mL** & **400 \(\mu\)L/mL** \\ \hline
**24** & 0.6 \({}^{\text{a}}\) & 4.3 \({}^{\text{b}}\) & 6.6 \({}^{\text{b}}\) & 0.5 \({}^{\text{a}}\) & 2.9 \({}^{\text{ab}}\) & 3.2 \({}^{\text{b}}\) \\ \hline
**48** & 0.6 \({}^{\text{a}}\) & 7.0 \({}^{\text{b}}\) & 7.9 \({}^{\text{b}}\) & 0.5 \({}^{\text{a}}\) & 7.8 \({}^{\text{b}}\) & 7.0 \({}^{\text{b}}\) \\ \hline \hline \end{tabular} Results are expressed as the diameter of the migration in cm. Ctrl: Control; 350 and 400 \(\mu\)L/mL of EAP solution. Different letters mean statistically significant differences (\({}^{\text{c}}\)\(p<0.05\)) compared to the control at the same time of incubation.  
\end{table} 
Table 4: EAP solution influence on swimming and swarming motility at 25 \({}^{\text{c}}\)C in _L. monocytogenes_ ATCC 7644 (strain S5). argued that the propolis acts on the permeability of the cellular membrane with disruption of membrane potential, thanks to hydrolytic enzymes production, which impairs the structure of the membrane [22]. On the other hand, several formulations of _Echinacea_ exhibit a promising antibacterial potential against different pathogenic bacteria, including those that provoke respiratory diseases [9]. The potent and selective antiviral and antibacterial properties of _Echinacea_ are due to the overturn of the proinflammatory cytokine stimulation, independently of the bacteria or virus that is causing the infection [23]. The immunomododulatory activities of _Echinacea_ have been attributed to the presence of glycoproteins, alkylamides and polysaccharides [23]. Moreover, the pronounced inhibitory effect of EAP may be attributable to its abundance in phenolic terpen, such as limonene (42.4%) and \(p\)-cymene (21.5%, Table 1), which display an arsenal of biological mechanisms of action as antioxidant, anti-inflammatory, anticancer and antimicrobial activities. Limonene and \(p\)-cymene affect the cytoplasmatic membrane with irreversible destruction of the lipids bilayer, bringing structural expansion and perturbation of membrane potential [24; 25]. Furthermore, the high concentration of \(p\)-coumaric (39.8%) and caffe acids (4.6%) can emphasize the antibacterial activity. The first could provoke irreversible permeability changes in the cell membrane, causing cells to lose the ability to maintain cytoplasm macromolecules and binding to DNA to inhibit cellular functions [26]. The caffeic acid has recently been discovered to generate reactive oxygen species upon photoirradiation by oxidation and to exert bactericidal activities [27]. However, in this study the EAP solution did not inhibit the bacterial motility capacity. _L. monocytogenes_ ATCC 7644 cells under treatment with 350 and 400 \(\mu\)L/mL displayed a more dynamic swarming and swimming motility over time, if compared to control conditions. This behavior could be a response to the stressing condition. The marked motility could be a bacterial defense mechanism, due to exposure to a hostile environment. In fact, previous studies have demonstrated that a sufficient concentration of motile cells can spontaneously form high-density clusters, affecting the collective tolerance to antimicrobial treatments that are lethal to planktonic cells [28; 29]. The antimicrobial activity exerted by the EAP solution on microorganisms with different origins and biological characteristics underlined the promising versatility of the extract, as a dietary supplement, food biopreservative or as a healing ointment. However, a comparison with similar natural products is not possible because of the limited availability of literature on such extracts. Therefore, the EAP solution deserves further attention to deepen the knowledge of its bioactivity and its possible _in situ_ application.