Abstract: In order to identify new anti-mycobacterial active natural products or new antibacterial synergists from medicinal plants,the anti-mycobacterial activity and synergetic antimicrobial effectof crude extract of Cirsium japonicum DC.was evaluated in this study.Boiled method,Soxhlet extraction method and ultrasonic methodwere used to extract whole plant of C.japonicum.Three kinds of extracts were subjected to antibacterial test in vitro by tube dish method and 96 microtiter plate dilution method.The results showed that when C.japonicum extract was used alone,the saturated concentration of C.japonicum water extract had no antimicrobial activity;and the MIC values of the Soxhlet extract and ultrasonic extract of C.japonicum were 8 mg/mL.The results showed that the antibacterial effect of ultrasonic extract of C.japonicum combined with the antibiotics was enhanced.Among them,ultrasonic extract of C.japonicum combined with chloramphenicol and erythromycin had obvious synergistic antibacterial effect against Mycobacterium smegmatis with the FIC index below 0.5.For the first time,this study has been found that there are antibacterial synergists in C.japonicum.It has laid a foundation for the identification of natural antibacterial products or antibacterial synergists from medicinal plants.

Key words: Cirsium japonicum DC., Mycobacterium smegmatis, antibacterial, synergists