## 2 Materials and Methods
### Antimicrobial and Antibiofilm Activity of Achillea millefolium Extract  
The _Achillea millefolium_ extract exhibited antimicrobial activity in the range of 2-16 mg/mL (MIC). The highest sensitivity (MIC = 2 mg/mL) was observed for _Candida albicans_, _Pseudomonas aeruginosa_, _Baellus subtilis_, and _Ralstonia solanacearum_, and the lowest for _Escherichia coli UPEC_ and _Enterococcus faecalis_ (MIC = 16 mg/mL). The MBC/MFC values were generally higher than the MIC values, suggesting a bacteriostatic effect (Table 3).  
These findings are in general agreement with the literature data. Several studies have reported that the antimicrobial efficacy of _A. millefolium_ extracts is strongly influenced by the choice of solvent and extraction technique. For example, [PERSON] et al. demonstrated that acetone and ethyl acetate extracts were active against Gram-positive bacteria at a concentration of 10 mg/mL, while Gram-negative bacteria were mostly resistant, with only a few _Pseudomonas aeruginosa_ strains showing sensitivity [18].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Extract** & **TP** & **TF** & **TPA** & **CT** & **DPPH** & **(\%)** & **FRAP (mmol/L \(\pm\) SD)** \\  & **(mg GAE/mL \(\pm\) SD)** & **(mg CE/mL \(\pm\) SD)** & **(mg CAE/mL \(\pm\) SD)** & **(mg DpE/mL \(\pm\) SD)** & **(\%)** & **FRAP (mmol/L \(\pm\) SD)** \\ \hline UAE & 50.06 \(\pm\) 0.09 \({}^{\text{a}}\) & 14.58 \(\pm\) 0.09 \({}^{\text{a}}\) & 3.31 \(\pm\) 0.04 \({}^{\text{a}}\) & 4.93 \(\pm\) 0.06 \({}^{\text{a}}\) & 70.00 \(\pm\) 0.14 \({}^{\text{a}}\) & 1.53 \(\pm\) 0.03 \({}^{\text{a}}\) \\ \hline SFE & 2.44 \(\pm\) 0.02 \({}^{\text{b}}\) & 0.041 \(\pm\) 0.00 \({}^{\text{b}}\) & 0.91 \(\pm\) 0.04 \({}^{\text{b}}\) & 0.79 \(\pm\) 0.03 \({}^{\text{b}}\) & 20.04 \(\pm\) 0.44 \({}^{\text{b}}\) & 0.77 \(\pm\) 0.04 \({}^{\text{b}}\) \\ \hline \end{tabular}
\end{table}
Table 2: Phytochemical composition of yarrow extract.  
Importantly, recent work has highlighted that the antimicrobial activity of _A. millefolium_ extracts can be further enhanced through combination strategies. Several studies have demonstrated that when the extract is combined with other bioactive agents, such as silver nanoparticles, nanoemulsion carriers, or even conventional antibiotics, a synergistic effect can be achieved, leading to a reduction in the effective MIC and a broader spectrum of activity. This approach not only improves the stability and bioavailability of the active compounds but also helps overcome the limitations of the use of the extract alone [25; 26].  
The anti-biofouling activity of _Achillea millefolium_ herb was also investigated in the present study. The antibiofilm properties of _Achillea millefolium_ herb (more than 50% biofilm reduction) were only observed for four strains of _Streptococcus apalactiae_, _Enterococcus faecalis_, and _Streptococcus mutans_ at concentrations of 4-8 mg/mL and for _Proteus mirabilis_ at a concentration of 8 mg/mL. These findings are partially consistent with literature reports; for example, [PERSON] et al. [18] observed significant inhibition of biofilm formation, especially among Gram-positive bacteria. However, the extent of biofilm disruption appears to be both strain- and concentration-dependent. Variability in antibiofilm activity may be attributed to differences in the cell wall structure and the intrinsic biofilm-forming capabilities of the microorganisms, as well as the unique chemical profile of the extract, determined by the extraction solvent. Such factors likely influence the diffusion and efficacy of bioactive compounds within the biofilm matrix [18].