## 4 Discussion  
Herbs such as _E. purpurea_ and _R. gravelens_ are commonly used for medical purposes, since they have many beneficial effects for humans [21; 22; 23; 24], but also animals, for which these herbs can serve as feed additives or alternative feed source [25; 26; 27]. It has also been shown that phages can be used as feed additives to reduce bacteria in animal preslaughter, without negatively impacting microbial communities [28]. Therefore, in our work, we tested the possible interactions of _Echinacea purpurea_ (L). Moench (EP) and _Ruta gravelens_ (RG) extracts and lytic phages as antibacterial agents (which can also serve as models of eukaryotic viruses) in the environment of bacteria. For this study, we have chosen well-known and studied phage models (phi6, MS2 and T4) from a certified collection, so the result interpretation will not be additionally complicated by using wild, unknown phages. Moreover, the selected phages were characterized by different sizes and specific features (Table 1) to ensure model diversity. Additionally, phage-matching bacterial hosts functioned as pathogens related to fauna and flora diseases (_P. syringae_ and _E. coli_). EP and RG methanol extracts revealed diverse and multidimensional interactions with the mixtures of phages and their bacterial hosts. In order to explain these interactions, it is necessary to draw general conclusions from the performed experiments and propose hypotheses explaining the results. The lysis profile experiment of the EP extract, at the concentration of 25% in combination with the MS2 phage and _E. coli_, resulted in limited phage lytic activity at the begging of the curve, then stimulating the growth of bacteria. The 6.25% concentration caused weakening of the phage lysis, and 0.049% generated similar lysis outcomes compared to the control lysis. These concentrations did not influence phage activity in the coincubation test, but stimulated the host cells during a modified MIC test (static conditions/no mixing), therefore the presented results are a consequence of the extract's concentration-dependent influence on bacteria that was more pronounced than the phage lytic activity. When the phi6 phage and _P. syringae_ were tested, the EP concentrations of 25% and 6.25% resulted in the lack of phage lysis (curves comparable to the control bacterial growth), while at 0.049%, the lysis curve was the same as the lysis control. The highest tested concentration (25%) also showed phagicidal activity, therefore the curve assay effect is the result of the  
Figure 6: SEM micrographs of the mixtures of bacteria _P. syringae_ and phage phi6 (**A**), compared to the same mixture of _P. syringae_ and phi6, but with the addition of 0.049% _Echinacea purpurea_ extract (**B**). extract influence on the phage. Since no phage killing effect was present in the coincubation test at the lower EP concentrations, the middle concentration (6.25%) is the result of the only extract effect on bacterial cells (or mixing could turn this concentration phagiicidal), which disappeared at a low concentration of 0.049%. The lack of EP 0.049% effect was also additionally proven by the SEM micrographs. When mixtures of EP extract with the T4 phage and _E. coli_ were studied, the highest EP concentration (25%) caused initial bacterial stimulation, followed by a slow decrease in the _E. coli_ proliferation after 6 h of incubation. The 6.25% EP extract resulted in a similar outcome, however the drop in bacterial biomass after 6 h was more pronounced. When the concentration of 0.049% was used, the curve was initially similar to the control growth curve, and after 10 h of incubation, a gradual decrease in the cell density was observed. The tested concentrations did not have any influence on the phage T4 in the coincubation assay, and it stimulated bacterial growth in the modified MIC assay; therefore, these results are again explained through the extract concentration-dependent stimulating influence on bacteria, that is stronger than the phage lytic activity.