Abstract: This study was conducted to investigate the inhibitory effects of tea water extracts against antibiotic-resistant Escherichia coli (E.coli) in order to provide information for the prevention and treatment of colibacillosis.The inhibitory activities of water extracts from red tea and green tea against antibiotic-resistant E.coli isolates from swine were determined by in vitro antibacterial test.The protective effect of water extracts of green tea with stronger inhibitory activity on mice challenged by antibiotic-resistant E.coli were observed in vivo. Results showed that the inhibitory activities against E.coli of two water extracts of tea increased with the increasing of their concentrations.The minimum inhibitory concentrations of water extracts of red tea and green tea against 13 tested E.coli strains were 62.5-250.0 and 62.5-125.0 mg/mL,respectively,which suggested that the water extracts of green tea presented stronger antibacterial activity.Two water extracts of tea presented different antibacterial activities against different strains of E.coli. At 48h post-challenge,all mice in the challenged group were dead,while survival rate of mice in the water extracts of green tea group was 20%;the villus height of duodenum and jejunum of mice in the water extracts of green tea group had no significant difference compared with the control group,while was higher (P<0.05) compared with the challenged group,which suggested that the water extracts of green tea presented mitigative effects to intestinal trauma caused by E.coli challenge.These findings indicated that water extracts of green tea presented stronger inhibitory effects against antibiotic-resistant E.coli, which could be used as an alternative bioactive substance for the prevention and treatment of colibacillosis.

Key words: water extracts of tea, Escherichia coli;antibacterial activity;protective effects