Synergistic Effect of the Ethanol Extract of Alismatis rhizoma against Oral Pathogens

Background: Alismatis rhizoma or Alisma orientale (Zexie in Chinese), the dried rhizome of Alisma orientale Juzepzuk (Alismataceae), is known to have diuretic and damp-heat clearing actions and has been used for the treatment of dysuria, edema, urinary tract infections, the retention of fluid and phlegm, and vertigo in Asia and Europe. Methods: In this study, the combination effect of the ethanol extract of Alismatis rhizoma (ARE) was evaluated against oral bacteria, either alone or with antibiotics, via broth dilution method and checkerboard and time kill assay. Results: In these results, MIC/MBC values for ARE against all the tested bacteria ranged between 313-5000/625-5000 microg/mL, for ampicillin 0.25-32/0.5-64 microg/mL and for gentamicin 4-32/8- 64 microg/mL respectively. Furthermore, the MIC and MBC were reduced to one half-twelve as a result of the combination of ARE with antibiotics. 1-2 hours of treatment with 1/2 MIC of ARE with 1/2 MIC of antibiotics resulted from an increase of the rate of killing in units of CFU/ mL to a greater degree than was observed with alone. Conclusions: These results suggest that the ARE is important in the antibacterial actions of oral pathogen agents.