Synthesis and long-term antibacterial performance of nano-montmorillonite-loaded polymyxin B (NMMT@PMB) against Salmonella in an ex vivo study

Salmonella is a Gram-negative bacterium causing intestinal infections. Polymyxin B (PMB) is an effective antibiotic against Salmonella , but the emergence of antibiotic resistance poses a growing concern. To address this challenge, this study synthesized a new nanocarrier by functionalizing nano-montmorillonite (NMMT) with PMB by adsorption, namely NMMT@PMB. PMB adsorption on NMMT followed the Langmuir isotherm and pseudo‑first‑order kinetics, and its release kinetics followed a diffusion-controlled mechanism. Although the minimum inhibitory concentration (MIC) of NMMT@PMB (2.78 and 44.54 µg/mL) was slightly higher than that of free PMB (2 and 32 µg/mL) for PMB-sensitive (S AT ) and resistant (S AT−P ) Salmonella typhimurium , the nanocarrier demonstrated sustained long‑term antibacterial activity over time. The antibacterial mechanism was the disruption of bacterial membrane integrity. Additionally, ex vivo results demonstrated that NMMT@PMB regulated the microbial community composition, increasing the relative abundance of probiotic bacteria (from 72.34% to 75.20%) and inhibiting pathogenic bacteria (from 8.54% to 2.36%), thereby facilitating its return toward the original state. These findings suggest that NMMT@PMB is a promising nano-delivery system that may support sustained antibacterial action and microbiota homeostasis, offering a potential strategy for improved management of Salmonella infections.