**5. Conclusions**

In conclusion, although the current European legislation admits the use of EOs as flavouring for animal foods, no previous study shows their potential ability to break down the intestinal biofilm of *Salmonella* spp. in livestock, when used at the concentrations admitted for flavouring. Furthermore, our results strongly confirm our hypothesis, since sub-MIC concentrations of both natural compounds interfere with microbial adhesion to intestinal target cells. Finally, sub-MIC concentrations of GR-OLI were able to reactivate the sensitivity of multi-resistant *Salmonella* spp. strains to ciprofloxacin, one of the most used antibiotics in veterinary practices. Our in vitro data, although needing confirmation with in vivo studies, lay the foundations for a new potential use of essential oil-based flavours in the fight against zoonosis. Indeed, although there are many studies on the antimicrobial activity of EOs, in the last 5 years, there is a paucity of articles aimed at evaluating the antimicrobial activity of single EOs on Salmonella spp. strains isolated from chicken and pig farms, and no clinical trial about the in vivo activity of EOs, or a mixture of these, on Salmonella spp. colonization has been published. In this article, for the first time, the potential preventive use of an EOs mixture used in feed as "flavourings" (GR-OLI) against *Salmonella* spp. strains directly isolated from chicken and pig farms has been shown.

**Author Contributions:** Conceptualization, M.D.V., P.M., F.B. and Y.Y.; Methodology, M.D.V., M.C., L.B.; Formal Analysis, M.D.V., M.C., C.M., S.B.; Investigation, M.D.V., L.B.; Resources, G.T., L.F.; Data Curation, M.D.C., M.C., L.B.; Writing—Original Draft Preparation, M.D.V., M.C., L.B., M.S. (Maurizio Scozzoli); Writing—Review & Editing, P.M., F.B., M.S. (Maurizio Sanguinetti). All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** Lori Morrison is gratefully acknowledged for manuscript proofreading.

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