Structure determines function. The main mechanism of antibacterial and bacteriostasis of plant extracts is its strong hydrophobicity in structure. Plant extracts can make the bacterial cell membrane and the phospholipid structure on the mitochondria separate, damage the cell structure, enhance the cell membrane permeability, resulting in the leakage of intracellular ions and contents, and then lead to bacterial cell death. For example, chlorogenic acid extracted from honeysuckle extract can combine with the cell membrane of Escherichia coli, increasing the permeability of the cell membrane, and the content of alkaline phosphatase in the treated Escherichia coli bacterial fluid increased, and the damage rate of Escherichia coli cells reached about 40%.
Plant extracts can also kill bacteria by inhibiting the synthesis of bacterial peptidoglycan to damage the morphology of the bacteria, such as Cylindroma root extract. In addition, its antibacterial mechanism also includes the destruction or degradation of bacterial cell wall, the destruction of cell plasma membrane, and the destruction of cell membrane protein structure, but also can make the bacterial cytoplasm aggregation, the cell proton movement weakened, and can also enhance the intestinal epithelial defense function to play the effect of bacterial infection. For example, berberine hydrochloride can make the α-hemolysin cells secreted by S. aureus distorted and deformed, making the cell surface uneven and leaking nutrients and genetic material. A large number of experimental studies have confirmed that the antibacterial effect of single active components is not as good as that of the whole plant extract, indicating that the effects of each component in the plant extract in vivo are mutually promoting. 
Different plant extracts regulate intestinal flora in different ways. Some can directly inhibit harmful bacteria through different ways, while some can promote the growth of probiotics and indirectly inhibit the reproduction of harmful bacteria. Some components of plant extracts, such as oligosaccharides, have obvious probiotic effects, which can promote the growth and reproduction of beneficial bacteria such as bifidobacterium and lactic acid bacteria in vivo and in vitro, and ultimately increase the number of beneficial bacteria while reduce the number of harmful bacteria. For example, Yucca shidigero extract can reduce the number of harmful bacteria such as Bacteroides and Eubacteria, and increase the number of Helicobacter in the intestinal tract of broilers. Aloe Vera Extract can reduce the death caused by Salmonella infection and the number of Salmonella in intestinal tract of broilers. Purslane extract can reduce the number of Escherichia coli in cecum and increase the number of Lactobacillus and Bifidobacterium.
