Abstract: Technological conditions for extraction of antibacterial active ingredient in Phryma leptostachya L.by ethanol was optimized.Then the extract was further extracted by a water immiscible organic solvent chloroform to enrich the effective antibacterial active ingredient (PAI).Extraction under the condition of ethanol volume fraction 80%,60 ℃,ratio of solid to liquid 1∶30 (g∶mL) and 4 h shows the optimal results,and the remaining aqueous phase raffinate after extraction with chloroform shows strong antibacterial activity.The diameter of inhibition zone for S.aureus and E.coli are (24.32±0.65) and (25.44±1.10) mm respectively,and the minimum inhibition concentration (MIC) are 6.25 and 3.12 g/L respectively.In addition,the bacterial growth curve,cell membrane permeability and cell morphology observation are applied to examine the inhibition mechanism on S.aureus and E.coli.Results show that PAI mainly effects on the logarithmic growth phase and destroys the permeability of the cell membrane as well as the structure of the cell wall;thus the bacteria are inhibited by multiple-hurdle effect.

Key words: Phryma leptostachya L.extract, extraction process, minimum inhibition concentration, antibacterial mechanism