## 6 Conclusions  
Many strategies have been developed for controlling the proliferation of pathogens. However, there is a critical need to release novel practical approaches such as combined therapies to stop the emergence of resistant species. The concerted use of two or more biocides that act simultaneously decreases the opportunities of life of the pathogenic microorganisms as well as their proliferation by promoting further mechanisms for microbe killing. This review shows the relevance of combining systems based on antimicrobial polymers that have been acquired in the last years. The synergy effect is demonstrated in many of the antimicrobial systems mentioned in this review when two agents working in tandem offer a greater than additive effect, resulting in combinations that are more potent than equivalent doses administered individually, which may reduce potential toxicity to mammalian cells and the cost of treatment. In most of the cases, antimicrobial polymers interact with the bacterial membrane provoking damage and favoring the action of the other biocidal. It was also noted that adding a third component typically increases the magnitude of the antimicrobial activity. Even if combinations do not provide enhanced or synergistic actions, they can broaden the antimicrobial spectrum and reduce the risk of initial inadequate treatments, which are often associated with increased mortality.  
In summary, polymers combined with other bioactive substances, synergistically acting in tandem, in antibacterial systems represent an important branch of medical research with broad perspectives. Nonetheless, how to improve the performance of these systems to achieve a level of practical application is our continuous pursuit. Perhaps, the combination with biopolymers or naturally occurring substances may provide dual systems acting in tandem with the potential for accessing a new generation of antibacterial polymers possessing a low health risk. Hopefully, our brief survey is helpful in understanding this strategy and will stimulate some new ideas for future developments.  
**Author Contributions:** The text was written as a collaborative effort between all authors.  
**Acknowledgments:**RYM and CGS also thank CONACyT (Consejo Nacional de Ciencia y Tecnologia, Mexico) and DAAD (Deutscher Akademischer Austauschdienst, Germany) for financial support within the framework of the funding program for international mobility PROALMEX 2015 (CONACyT project: 267752 and DAAD project: 57271725). USS and CGS gratefully acknowledge the support of the DFG (Deutsche Forschungsgemeinschaft, Germany)-funded Collaborative Research Center PolyTarget (SFB 1278, projects Z01 and B02). MAJT acknowledges the support of the CONACYT through project CB-2015/253303. The support of the CONACYT through Grant 299092 (LANIAUTO) is greatly appreciated.  
**Conflicts of Interest:** There are no conflicts to declare.  
**Nomenclature**  
AgBr silver bromide AgNPs silver nanoparticles AM acrylamide AMR antimicrobial resistance AuNPs gold nanoparticles BPAM benzophenone based quaternary ammonium molecules CMPS macroporous crosslinked chloromethylated polystyrene CNTs carbon nanotubes CS chitosan CuNPs copper nanoparticles DADMAC diallyl dimethyl ammonium chloride DMDEPAC \(NN\)-dimethyl-\(N\)-dodecyl-\(N\)-(1,2-epoxypropyl) ammonium chloride DMOEPAC \(N\)-\(N\)-dimethyl-\(N\)-octadecyl-\(N\)-(1,2-epoxypropyl) ammonium chloride DNA deoxyribonucleic acid GMs graphene-based materials GO graphene oxide MIC minimum inhibitory concentration MMT montmorillonite