Eugenol nanoemulsion protects chickens against S. Typhimurium infection by improving cecal barrier function and alleviating oxidative stress and inflammation.

To address the poor water solubility and high volatility of eugenol (EU), this study developed an EU nanoemulsion (NanoEU) and evaluated its anti-Salmonella enterica serovar Typhimurium (S. Typhimurium) activity and protective effects against S. Typhimurium infection in vitro and in vivo. NanoEU showed a uniform milky-white appearance, an average particle size of 137.53 ± 5.07 nm, and a PDI of 0.23 ± 0.03. It exhibited in vitro antibacterial activity, with MIC and MBC values of 512 μg/mL and 1024 μg/mL, respectively. No hemolysis was observed in chicken erythrocytes at 128-1024 μg/mL, indicating preliminary biosafety. NanoEU also maintained stable appearance and unchanged antibacterial activity during 30 days of storage at 4 °C and 25 °C. A chicken model of S. Typhimurium infection was established to assess the protective roles of NanoEU. The results showed that NanoEU partially alleviated impaired body weight gain, reduced bacterial loads in the cecum, liver, and spleen, and mitigated histopathological damage. In addition, NanoEU improved cecal mucus secretion, upregulated tight junction-related gene and protein expression, alleviated local oxidative stress and inflammatory responses. In conclusion, NanoEU exhibited anti-S. Typhimurium activity, preliminary biosafety, and favorable storage stability. More importantly, it exerted both anti-infective and host-protective effects in vivo, suggesting its potential application in controlling S. Typhimurium infection and reducing antibiotic use in poultry.