Abstract: The experiment was conducted to screen Chinese medicine which had good antibacterial effect in vitro of Riemerella anatipestifer. To extract the effective component of Cortex Eucommiae and other traditional Chinese medicine were by means of ultrasonic processing, ethanol and water bath heating, using tube double dilution method to determining the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the extracts against Riemerella anatipestifer, determined the effect on the united bacteriostasis extracts of traditional Chinese medicine on Riemerella anatipestifer through thechessboard method. The results showed that the MIC ranged from the extracts of Cortex Eucommiae and other Chinese medicines on Riemerella anatipestifer were 15.60 to 250.00 mg/mL. The MIC of Cortex Eucommiae, Radix et Rhizoma Rhei, Radix Isatidis, Fructus Citri Sarcodactylis, Cortex Fraxini and Isatidis Foliumwere all 15.60 mg/mL. But the MIC of Flos Lonicerae Japnicae, Rhizoma Curcumae Longae, Radix Scutellariae, Radix Astragalus and Radix Arnebia were more than 125.00 mg/mL. Through a combination of antimicrobial, we could discovery that Cortex Eucommiae combined with Cortex Fraxini had additive effects, Radix Pulsatilla combined with Cortex Eucommiae and Cortex Fraxini were independent of the united, Radix Pulsatilla combined with Radix et Rhizoma Rhei performance antagonism. Therefore, Cortex Eucommiae, Radix et Rhizoma Rhei, Radix Isatidis, Fructus Citri Sarcodactylis, Cortex Fraxini and Isatidis Folium had good effects on Riemerella anatipestifer in vitro. Flos Lonicerae Japnicae, Rhizoma Curcumae Longae, Radix Scutellariae, Radix Astragalus and Radix Arnebia had no effect on Riemerella anatipestifer. Cortex Eucommia, Cortex Fraxini and Radix Pulsatilla could form a prescription inhibition on Riemerella anatipestifer.

Key words: Chinese traditional medicine; Riemerella anatipestfer; antibacterial activity in vitro