## 4 Conclusions  
This research identifies a dual function for zinc salts, which act as both antimicrobial compounds and modulators of biofilms. Strain differences in zinc tolerance nonetheless indicate that intrinsic resistance mechanisms in bacteria, such as efflux pumps and \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**ABG**} & \multicolumn{3}{c}{_E. faecalis_** ATCC 19433**} & \multicolumn{3}{c}{_E. faecalis_** ATCC 29212**} \\ \cline{2-7}  & **PC** & **ZnSO\({}_{4}\times\)7H\({}_{2}\)O** & **ZnCl\({}_{2}\)** & **PC** & **ZnSO\({}_{4}\times\)7H\({}_{2}\)O** & **ZnCl\({}_{2}\)** \\ \hline DXT 30 & 15.50 \(\pm\) 0.71 & 17.50 \(\pm\) 0.71 & 12.50 \(\pm\) 0.71 & 11.00 \(\pm\) 0.00 & 13.50 \(\pm\) 0.71 & 15.00 \(\pm\) 0.00 \\ AML 30 & 20.00 \(\pm\) 0.00 & 21.50 \(\pm\) 0.71 & 19.00 \(\pm\) 1.41 & 20.00 \(\pm\) 0.00 & 27.00 \(\pm\) 0.00 & 27.00 \(\pm\) 0.00 \\ MEZ 75 & 20.50 \(\pm\) 0.71 & 23.50 \(\pm\) 0.71 & 21.50 \(\pm\) 0.71 & 26.00 \(\pm\) 1.41 & 25.00 \(\pm\) 0.00 & 28.50 \(\pm\) 0.71 \\ CXM 30 & 17.50 \(\pm\) 0.71 & 19.50 \(\pm\) 0.71 & 17.00 \(\pm\) 0.00 & 16.00 \(\pm\) 1.41 & R & R \\ CAZ 30 & 22.00 \(\pm\) 0.00 & 24.00 \(\pm\) 0.00 & 22.00 \(\pm\) 0.00 & 10.50 \(\pm\) 0.71 & R & R \\ CRO 30 & 27.50 \(\pm\) 0.71 & 29.00 \(\pm\) 0.00 & 26.00 \(\pm\) 1.41 & 20.00 \(\pm\) 0.00 & R & R \\ AMP 2 & R & R & 10.00 \(\pm\) 0.00 & 14.50 \(\pm\) 0.71 & 15.50 \(\pm\) 0.71 \\ AUG 30 & 19.00 \(\pm\) 0.00 & 18.50 \(\pm\) 0.71 & 18.00 \(\pm\) 0.00 & 24.00 \(\pm\) 0.00 & 26.00 \(\pm\) 0.00 & 25.00 \(\pm\) 0.00 \\ CAL 40 & 23.50 \(\pm\) 0.71 & 25.00 \(\pm\) 0.00 & 16.00 \(\pm\) 1.41 & 12.00 \(\pm\) 0.00 & R & 13.50 \(\pm\) 0.71 \\ CIP 5 & 31.50 \(\pm\) 0.71 & 30.00 \(\pm\) 0.00 & 27.50 \(\pm\) 0.71 & 20.00 \(\pm\) 0.00 & 20.00 \(\pm\) 0.00 & 21.00 \(\pm\) 1.41 \\ CN 30 & 21.50 \(\pm\) 0.71 & 21.50 \(\pm\) 0.71 & 20.00 \(\pm\) 0.00 & 17.50 \(\pm\) 0.71 & 15.00 \(\pm\) 0.00 & 20.00 \(\pm\) 0.00 \\ CN 10 & 19.50 \(\pm\) 0.71 & 19.50 \(\pm\) 0.71 & 17.00 \(\pm\) 0.00 & 11.50 \(\pm\) 0.71 & 10.50 \(\pm\) 0.71 & 17.00 \(\pm\) 0.00 \\ K 30 & 18.50 \(\pm\) 0.71 & 17.50 \(\pm\) 0.71 & 16.50 \(\pm\) 0.71 & 25.50 \(\pm\) 0.71 & 10.00 \(\pm\) 0.00 & 12.00 \(\pm\) 0.00 \\ TOB 10 & 18.00 \(\pm\) 0.00 & 19.00 \(\pm\) 0.00 & 19.50 \(\pm\) 0.71 & 26.00 \(\pm\) 1.41 & 10.00 \(\pm\) 0.00 & 14.00 \(\pm\) 0.00 \\ TE 30 & 12.00 \(\pm\) 0.00 & 13.00 \(\pm\) 0.00 & 16.00 \(\pm\) 1.41 & 11.50 \(\pm\) 0.71 & 12.00 \(\pm\) 0.00 & 14.00 \(\pm\) 0.00 \\ \hline \end{tabular}  
* PC—positive control, nontreated strains; R—resistant. The data represent zones of inhibition in mm.  
\end{table} 
Table 4: The antibiotic susceptibility for _E. faecalis_. metal sequestration activities, contribute profoundly to susceptibility to zinc. The findings confirm that high concentrations of zinc chloride and zinc sulfate heptahydrate are effective in inhibiting biofilm formation. In contrast, sub-inhibitory concentrations induce biofilm production, particularly in _E. coli_ and _E. faecalis_, as a survival mechanism. This finding aligns with current research indicating that exposure to sub-lethal metal concentrations can enhance bacterial resistance by promoting biofilm formation and altering antibiotic susceptibility. Based on these findings, zinc antimicrobial strategies should be carefully optimized to prevent the unintended emergence of resistance in clinical and industrial applications. One limitation of this study is the use of well-characterized ATCC reference strains, which, while consistent and widely used in laboratory research, may not fully represent the genetic and phenotypic diversity of environmental isolates found in actual pipeline systems. These variables can affect biofilm formation, metal-microbe interactions, and antimicrobial efficacy in ways that experiments cannot replicate. Additionally, the anti-biofilm activity was assessed using crystal violet staining and absorbance measurements, which quantify total biofilm biomass but do not differentiate between viable and non-viable cells.