Abstract: Abstract：The minimum inhibitory concentrations (MIC) of Herba Taraxaci, trimethoprim and Herba Taraxaci combined with Trimethoprim against Staphylococcus aureus, Escherichia coli and Salmonella were measured individually by the method of microdilution checkerboard techniques. Then the fractional inhibitory concentrations (FIC) indices of Herba Taraxaci combined with Trimethoprim were calculated. The results showed that the FIC values on Staphylococcus aureus, Escherichia coli and Salmonella were respectively 0.75, 0.75,1. The effect of their combination taken on additive action. The number of Staphylococcus aureus, Escherichia coli and Salmonella which had been inhabited by Herba Taraxaci combined with Trimethoprim for 1 h, 2 h, 4 h and 8 h, were enumerated by plate counts methods. Then the killing rate of Herba Taraxaci combined with Trimethoprim were calculated. The experimental data were fitted by least squares method. The optimal dose of Trimethoprim which combined with Herba Taraxaci against Staphylococcus aureus, Escherichia coli and Salmonella in vitro, were respectively 4.0 mg/g,1.8 mg/g and 2.0 mg/g. 

Key words: Key words：Herba Taraxaci; Trimethoprim; synergistic antibacterial action