Abstract:Chitosan’s antibacterial effect and mechanism against Serratia liquefaciens were studied.The minimal inhibitory concentration（MIC）of chitosan on S. liquefaciens was determined.To comprehensively analyze chitosan’s effect on S. liquefaciens，bacterial growth curve，cell wall and cell membrane integrity（conductivity，extracellular nucleic acid content，extracellular protein content，alkaline phosphatase activity），and cell enzyme activity（catalase，superoxide dismutase）before and after chitosan treatment were measured while the changes in cell morphology of S. liquefaciens were observed with the electron microscope. The results showed that the MIC of chitosan against S.liquefaciens was 6 mg/mL.After chitosan treatment，the growth of S.liquefaciens was inhibited，and conductivity，as well as the content of extracellular nucleic acid，extracellular protein，and alkaline phosphatase increased. Cell wall and cell membrane integrity were destroyed. Catalase and superoxide dismutase activity was reduced，normal cell metabolism was disrupted and the cells were injured.According to scanning electron microscopy observation，the morphology of the bacteria was abnormal with rough cell membrane surface and crumpled cells. In conclusion，chitosan was able to change S. liquefaciens’cell wall and cell membrane integrity，disrupting its normal metabolism and distorting the cell morphology，thus effectively controlling its growth.