Abstract: This study aimed to investigate the antibacterial activity of matrine against bovine Streptococcus agalactiae in vitro, and to provide theoretical basis for the development of monomer antibacterial products of Chinese herbal medicine. In this study, the bacteriostatic activity of matrine against Streptococcus agalactis was analyzed by determining the minimum inhibitory concentration and bacteriostatic curve. In the mean time, whole blood killing test, adhesion test, biofilm staining and electron microscopic observation were used to explore the effects of matrine on the resistance of Streptococcus agalactis to organism killing, host adhesion and biofilm formation. The results showed that matrine could effectively inhibit the proliferation of Streptococcus agalactiae (ATCC13813) in vitro, and the minimum inhibitory concentration of matrine against Streptococcus agalactiae was 4 mg·mL^-1, the biofilm formation of S. agalactiae was decreased as well. Scanning transmission electron microscopy showed that the surface of the cell membrane of Streptococcus agalactiae shrank, the cell wall became smooth and thin, and the formation of capsule was significantly inhibited. Matrine could significantly inhibit the adhesion of Streptococcus agalactiae to mammary epithelial cells. Quantitative PCR showed that matrine significantly decreased the expression of virulence genes ScpB, CpsA, CylE and CAMP which related to invasion and immune evasion (P<0.05), and significantly up-regulated the expression of CpsE gene (P<0.05). In addition, matrine significantly decreased the expression of Bac, Bca, Lmb, BIBA, PI-2b and FbsB genes which related to the adhesion of virulence factors (P<0.05). These results indicate that matrine can achieve the antibacterial effect by inhibiting the proliferation of Streptococcus agalactiae (ATCC13813) in vitro, destroying the integrity thus decreasing the invasion of the strain.

Key words: matrine, Streptococcus agalactiae, whole blood killing, adhesion ability