**4. Conclusions**

The polyphenol fraction present in EVOO oil confirms once again its antibacterial properties. The different qualitative and quantitative profile of polyphenols present in a PF extract can affect in a different way its antibacterial effectiveness. The statistical method herein applied is easy and useful to predict the synergistic effect of polyphenols and the influence that each of them has—based also on their amount—on the activity of the whole extract. In a future perspective this could be a basis of possible complementary studies, for example, to formulate ideal drugs of natural origin, composed of optimal mixtures of polyphenols which are able to exercise with the minimum effort (in terms of quantity) and the maximum result (against the greatest number of pathogens) their antibacterial efficacy.

**Author Contributions:** Conceptualization and Investigation, F.N., F.F., A.G.C. and A.d.A.; methodology, F.N., F.F., R.C., L.M., A.M., V.D.F.; Formal analysis, A.d.A.; writing—original draft preparation, F.N., A.d.A., V.D.F.; writing—review and editing, F.N., A.d.A., V.D.F.; funding acquisition, F.N.

**Funding:** The Campania Regional Council, Italy within the Project funded this research: "Salvaguardia della Biodiversità Vegetale della Campania" ("SALVE"), PSR 2007–2013, mis 214, action f2.

**Conflicts of Interest:** The authors declare no conflict of interest.
