Polyprenols of Ginkgo biloba Enhance Antibacterial Activity of Five Classes of Antibiotics

Polyprenol (GBP) from Ginkgo biloba Leaves (GBL) is an important lipid with many bioactive effects. The effect of GBP on antibacterial properties of five antibiotics belonging to different classes was through analysis of inhibition halos, MIC, and FIC index. And we studied the time-killing curves and Ca(2+) mobilization assay in Staphylococcus aureus cells treated with GBP microemulsion and gentamicin sulfate under MIC/2 conditions. These results showed that the GBP microemulsion (average diameter 90.2 nm) combining with gentamicin sulfate had the highest enhancing antibacterial effect against Staphylococcus aureus, and the MIC value was 33.0 μg/mL. The increase of the antibacterial effect of tested antibiotics was positively correlated with the decrease of the average diameter of GBP microemulsion. Moreover, GBP microemulsion enhanced antibacterial effect and prolonged antibacterial time of GBP combining with gentamicin sulfate against Staphylococcus aureus. GBP microemulsion could enhance the ability of gentamicin inducing an increase in intracellular calcium concentrations to Staphylococcus aureus. GBP microemulsion could help some classes of antibiotics to inhibit or kill bacteria. This study supports the fact that GBP microemulsion obviously can not only reduce the dosage of some classes of antibiotics, but also reduce the frequency of the antibiotic use in vitro.