AGROALNEXT Project: New bioactive compounds from aromatic and medicinal plants in reducing antibiotic use. Impact on antimicrobial resistance in livestock.

Concentrations of carvacrol (>50%) and p-cymene (≥10%) in the active ingredients (AEOs) of the species *Th. zygis*, *Th. hyemalis*, and *Th. capitata* ensure adequate efficacy against the studied pathogenic bacteria. Optimization of the nanoencapsulation of active ingredients, considering different chitosan structures (medium and low molecular weight) and chitosan/AEO ratios, allows us to conclude that ratios of 0.5% and 1% are stable with an active duration of up to 90 days. The chitosan/AEO ratio of 1% significantly improves the efficacy of the AEOs against all the bacteria studied. The structure of the chitosan affects the effectiveness of these formulations. In this regard, efficacy against most Gram-negative bacteria and *Enterococcus faecalis* (Gram-positive) improves significantly with the use of low molecular weight chitosan. However, for Staphylococcus aureus and S. epidermidis (Gram-positive), effectiveness increases with the use of medium molecular weight chitosan. The use of these non-steroidal anti-inflammatory drugs (NSAIDs) in low molecular weight chitosan is proposed as a tool to improve animal digestive health.