## 4 Conclusions  
In this study, a high-potential polystyrene-based cationic resin (R4) was developed and tested for use as a new low-cost production material in sanitization systems to reduce bacterial contamination in water. In particular, it was fabricated by a simple one-step reaction by copolymerizing 4-ABSTY with DMAA and using AAEA as a cross-linker. Since R4 has intrinsic broad-spectrum antibacterial effects without needing to be enriched with additional antibacterial agents, it does not suffer from a typical problem of most materials used for water decontamination, which are likely to release the included antibacterial molecules during use, thus losing their antibacterial efficiency over time. The presence of all ingredients (4-ABSTY, DMAA, and AAEA) in R4 was confirmed by ATR-FTIR spectroscopy. The fractionation by sieving of R4 provided a central body of particles (>96% of the total quantity sieved) with a little dispersed granulocyte. R4 was characterized by several other analytical techniques, which showed a spherical morphology and micro-dimensioned particles (microspheres), endowed with high hydrophilicity, large swelling capability in water, very high and homogeneous porosity, and the capability to return to the original structure after swelling. The content of NH\({}_{3}\)\({}^{+}\) groups, essential for allowing electrostatic interactions with the negatively charged surface of bacteria and to capture, inhibit, and/or kill them, was determined both by following the method of [PERSON] and [PERSON] and by the results from potentiometric titrations. The antibacterial properties of R4 were first assessed by performing time-kill experiments up to 4 h of exposure on MDR clinical isolates of _E. coli_, _S. aureus_, and _Salmonella_ and _Enterococcus_. Subsequently, similar experiments were conducted by simulating a hypothetical disinfection system (consisting of a column containing R4 and using a model of water that was artificially contaminated with fecal species such as _E. coli_, Group B _Salmonella_ species, _E. fiecium_, and _E. faecalis_). These experiments established that the optimal contact time between R4 and water for achieving the death of more than 99% of bacteria is 4 h.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/polym14214690/s1](https://www.mdpi.com/article/10.3390/polym14214690/s1)]([https://www.mdpi.com/article/10.3390/polym14214690/s1](https://www.mdpi.com/article/10.3390/polym14214690/s1)), Figure S1. Appearance of the obtained swelled R4 from hydrating the dry resin with an excess of 10 mL of water and recovered by centrifugation at 4000 rpm for 30 min: test tube in the normal vertical position (a) and in the inverted position (b). Figure S2. Column filled with R4 when in contact with the aqueous model of contaminated water (a) and after filtration (b). Figure S3. Variation in the Log\({}_{10}\) (CFU/mL) of _E. coli_ 224 when exposed to R4 (_E. coli_ 224 (R4)) in a column imitating a sanitation system for 1, 2, 4, and 24 h of exposure vs. control (_E. coli_ 224). Figure S4. Percentage of the bacterial cells killed by R4 in a column imitating a sanitation system after 1, 2, 4, and 24 h of exposure when tested against _E. coli_ 224. Table S1. Weights and cumulative weight loss (%) of R4 determined at times T\({}_{0}\)-T\({}_{7}\). Table S2. Weights of R4 at times T\({}_{0}\)-T\({}_{3}\) and the cumulative swelling ratio percentages. **Author Contributions:** Conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, visualization, supervision, project administration, writing--original draft preparation, S.A.; writing--review and editing, S.A. and A.M.S. ; microbiologic experiments, A.M.S., D.C. and G.P. All authors have read and agreed to the published version of the manuscript. **Funding:** This research received no external funding. **Data Availability Statement:** All data referred to this study are included in the present manuscript.