## 5 Conclusions  
This study demonstrates the antimicrobial and antib biofilm potential of copper sulfate and copper nitrate against _E. coli_ and _E. faecalis_, two common contaminants in pipeline systems. Copper salts exhibited clear dose-dependent effects, with concentrations between 1.56 and 100 mg/mL resulting in significant inhibition of bacterial growth and biofilm formation. For instance, at 100 mg/mL, complete growth inhibition was observed in both bacterial species. However, sublethal concentrations in the range of 0.39-0.78 mg/mL paradoxically enhanced biofilm strength in _E. faecalis_, shifting its classification from moderately to strongly adherent. Regarding antibiotic susceptibility profiles, copper salts did not significantly alter antibiotic resistance profiles for most results, but a change in resistance to ceftazidine was observed in _E. faecalis_. The observed potential for increased antibiotic susceptibility or resistance in specific cases underscores the need to manage copper usage carefully. Because of this, this paper further highlights the need to find the optimal concentration of copper salts that are effective, non-toxic, and compliant with water quality standards. To determine whether sodium nitrate or sodium sulfate contributes independently to the inhibition of bacterial growth or the modulation of biofilms, future research could include additional controls employing these anions. Moreover, since nanoparticles have demonstrated encouraging antimicrobial qualities, this study could be expanded in the future by contrasting the efficacy of alternative copper forms, such as copper nanoparticles, with conventional copper salts. Additionally, transcriptomic or proteomic analyses could be used to better understand the mechanisms behind the development of resistance and the antimicrobial effects induced by copper. Future studies could also incorporate surface visualization techniques such as 2D/3D mesh plotting or SEM imaging to investigate how copper salts alter biofilm architecture at the structural level.  
Conceptualization, M.A. and A.E.S.; methodology, N.C., M.L. and S.D.; validation, A.E.S, A.P. and M.H.; formal analysis, N.C.; investigation, N.C., M.L. and S.D.; data curation, N.C., M.L. and S.D.; writing--original draft preparation, N.C. and M.L.; writing--review and editing, M.A., A.P. and M.H.; visualization, N.C.; supervision, A.E.S. and M.A.; project administration, A.E.S. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The original contributions presented in this study are included in the article.  
The research that has produced this research paper has been financially supported by the European Union through the project Introducing Student Research Mobilities to BH Unis--INSTREAM, implemented by a consortium led by International Burch University, but does not necessarily represent the official position of the European Union or International Burch University and is the sole responsibility of the author.  
Author [PERSON] was employed by the company ALLINS LLC LP. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.