Preventing Salmonella Choleraesuis infection by Mume Fructus-Schisandra formulas through the "membrane...

The strong pathogenicity and environmental adaptability of Salmonella Choleraesuis cause significant losses to the pig breeding industry, and existing prevention and control strategies (such as the abuse of antibiotics and limitations in vaccine development) are urgently needed for optimization. This study aims to screen green prescriptions against S. choleraesuis from Chinese herbal medicines that possess both medicinal and edible value, providing a basis for the development of green feed additives.

In this study, 10 Chinese herbal medicines from the Catalog of Feed Raw Materials were screened for antibacterial activity and synergistic compatibility via microbroth and microcheckerboard dilution assays. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the prescription against S. choleraesuis were determined. And the antibacterial activity was detected by extracellular potassium ion concentration, total leakage rate, transmission electron microscopy, and RT-qPCR analyses.

The optimal compound composition was determined via L9 (3⁴) orthogonal tests as follows: Mume Fructus, 30 g; Schisandrae Chinensis Fructus, 10 g; Crataegi Fructus, 5 g; and Atractylodes lancea, 5 g. Its MIC and MBC against S. choleraesuis were 15.625 mg/mL and 31.25 mg/mL, respectively. Furthermore, extracellular potassium ion concentration, total leakage rate, transmission electron microscopy, and RT-qPCR analyses demonstrated that the compound increased bacterial cell membrane permeability, disrupted bacterial flagella, detached cell membranes from cell walls, induced irregular vacuole formation, and severely impaired the structural integrity of certain bacterial cells. In addition, compound prescription inhibited the transcription levels of key genes in the type III secretion system (T3SS) (sipA/B/C, invA/F, prgH/I, spaP, hilA/D, p < 0.01). A mouse diarrhea model was established with 5 × 10⁴ CFU/mL S. choleraesuis. After 7 days of treatment (10 g/kg), the protection rate reached 66.7%. It significantly increased sIgA in the mice and downregulated the expression of inflammatory factors (TNF-α, IL-1β, and IL-6; p < 0.01).

The screened Chinese herbal prescription has significant antibacterial activity against S. choleraesuis both in vitro and in vivo. The prescription acts against S. choleraesuis through a multitarget mechanism of "membrane damage-virulence inhibition-immune regulation," which provides theoretical support for the prevention of S. choleraesuis and the development of green feed additives.