Preparation of controlled-released starch-alginate microspheres loaded with thymol nanoemulsions and their therapeutic effects on salmonellosis

The rise of antimicrobial resistance has spurred interest in natural alternatives such as thymol, a potent broad-spectrum antibacterial agent. However, its clinical potential for treating enteric infections is severely limited by poor stability, low bioavailability, inherent cytotoxicity, and non-targeted release. To overcome these challenges, thymol nanoemulsion was firstly prepared and then incorporated into starch‑sodium alginate microspheres (TMS). This system was comprehensively characterized and evaluated for its antibacterial efficacy, safety, and therapeutic performance both in vitro and in a Salmonella -infected mice. Our findings demonstrate that TMS achieved high encapsulation efficiency, provided targeted sustained release in the intestinal environment (>85%), and exhibited potent antibacterial and anti-biofilm activity primarily through membrane disruption. By facilitating the sustained colonic release of thymol nanoemulsion, TMS effectively prevented local irritation while providing systemic anti-infection protection, as evidenced by the mitigation of symptoms such as weight loss, bacterial dissemination, and splenomegaly. Moreover, TMS restored gut homeostasis by preserving intestinal barrier integrity, enriching beneficial microbiota (e.g., Lactobacillus , Muribaculaceae ), and rescuing host energy metabolism via upregulation of the tricarboxylic acid cycle (TCA cycle) and the activated protein kinase (AMPK) signaling pathway. This work establishes a safe, multifunctional oral delivery platform that synchronously enhances the therapeutic efficacy and eliminates adverse effects of thymol.