Inhibitory activity of flavonoids fraction from Astragalus membranaceus Fisch. ex Bunge stems and leaves on Bacillus cereus and its separation and purification.

Fisch. ex Bunge is a traditional botanical drug with antibacterial, antioxidant, antiviral, and other biological activities. In the process of industrialization of , most of the aboveground stems and leaves are discarded without resource utilization except for a small amount of low-value applications such as composting. This study explored the antibacterial activity of stem and leaf extracts to evaluate its potential as a feed antibiotic substitute. The antibacterial activity of the flavonoid, saponin, and polysaccharide fractions in stems and leaves was evaluated by the disk diffusion method. The inhibitory activity of the flavonoid fraction from stems and leaves on was explored from the aspects of the growth curve, cell wall, cell membrane, biofilm, bacterial protein, and virulence factors. On this basis, the flavonoid fraction in stems and leaves were isolated and purified by column chromatography to determine the main antibacterial components. The flavonoid fraction in stems and leaves had significant inhibitory activity against , and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were 1.5625 and 6.25 mg/mL, respectively. stem and leaf flavonoid fraction can induce death of in many ways, such as inhibiting growth, destroying cell wall and cell membrane integrity, inhibiting biofilm formation, inhibiting bacterial protein synthesis, and downregulating virulence factor expression. In addition, it was clear that the main flavonoid with antibacterial activity in stems and leaves was isoliquiritigenin. Molecular docking showed that isoliquiritigenin could form a hydrogen bonding force with FtsZ. stem and leaf flavonoid fractions had significant inhibitory activity against , and the main chemical composition was isoliquiritigenin.