RESUMEN
Objective To evaluate the inhibitory activity of Herba Taraxaci extract on Escherichia coli DH5α (E. coli DH5α) and to investigate proteomic response of E. coli. Methods Medicinal powder of Herba Taraxaci was extracted with the solvents of different polarity ( n-hexane, ethyl acetate, distilled water) , and then the obtained 8 different extracts were subjected to thin layer chromatography ( TLC) analysis. Microdilution method was performed to detect the minimum inhibitory concentration ( MIC) of different extracts and the growth curves were described. The protein expression profiles of E . coli treated with the extracts were analyzed by sodium dodecyl sulfate polyacrylamide gel electropheresis ( SDS-PAGE) and two dimensional electrophoresis (2-DE) . Results Water decoction of Herba Taraxaci could obviously suppress the growth of E. coli with a MIC of 1.95 mg/mL. The different extractions exhibited no antibacterial activity except ethyl acetate phase 3 with a MIC of 0.13 mg/mL, which was equal to 19.23 mg/mL of crude drugs. The results of TLC analysis showed that chlorogenic acid was undetectable in n-hexane extract and ethyl acetate phase 1 extract, and ethyl acetate phase 2 and 3 extracts showed obviously increased spots. The results of SDS-PAGE and 2-DE showed that water decoction of Herba Taraxaci had inhibitory effect on the expression of functional protein. The results of 2-DE showed that after treatment with ethyl acetate phase 3 at the concentration of 2 × MIC for 21 hours, the amount of protein spots were 92 less than those of the blank control group, the spots of E. coli DH5α soluble protein with expression amount down-regulated doubly were 24, and those with expression amount up-regulated doubly were 19. Ethyl acetate phase 3 extract had an effect on down-regulating the protein expression of E. coli DH5α soluble protein pH3-10, and water decoction of Herba Taraxaci had inhibitory effect on E. coli DH5αprotein expression. Conclusion Herba Taraxaci has significant antibacterial activity on E. coli DH5α, and the water-soluble fraction of chlorogenic acid and caffeic acid might be the active components. The possible antibacterial mechanism may be related with the regulation of bacterial protein expression.