Abstract: Staphylococcus pseudintermedius is the main pathogenic bacterium of canine pyoderma, which has multi-drug resistance and serious threat to the health of dog and human. In this study, 20 strains of Staphylococcus pseudintermedius were isolated from dogs with pyoderma, and the antibacterial activity and antibacterial mechanism of rhein against Staphylococcus pseudintermedius were revealed. In this study, the antibacterial activity of rhein against Staphylococcus pseudintermedius was determined by minimum inhibitory concentration, minimum bactericidal concentration, bacteriostatic curve and adhesion assay. The cell membrane integrity and permeability, ROS level of Staphylococcus pseudintermedius were detected after rhein treated. The morphology and ultrastructure of bacterial cells were observed by electron microscopy, so as to explore the antibacterial mechanism of rhein against Staphylococcus pseudintermedius. The results showed that the minimum inhibitory concentration of rhein against Staphylococcus pseudintermedius was 12.5 μg·mL^-1, and subinhibitory concentration could significantly inhibit the growth and adhesion. The permeability of bacterial cell membrane was changed and the activity of β-galactosidase was increased after treated with rhein (P<0.05). The results of ROS assay showed that the level of ROS increased by 3.9 times (1×MIC) and 6.4 times (2×MIC) after rhein treatment. Electron microscopy showed that the morphology was changed after rhein treatment, there was abundant secretions on the cell surface and it was shrunk, the cell wall was broken, electron density was reduced, and the contents was leaked. This study indicate that rhein can destroy cell membrane integrity and permeability, and induce bacterial cells to produce a lot of ROS to achieve antibacterial effect.

Key words: rhein, Staphylococcus pseudintermedius, antimicrobial activity, antimicrobial mechanism