The synergistic effect of shikonin and ebselen against Staphylococcus aureus

Abstract:

[Objective] To explore the synergistical effect and mechanism of the shikonin and ebselen against S. aureus.[Methods] We used spectrophotometry assay to determine the antibacterial effect of shikonin-ebselen on S. aureus, propidium iodide (PI) staining to detect the bactericidal effect of shikonin-ebselen, and the transmission electron microscope to observe the S. aureus morphological changes after the shikonin-ebselen treatment. We used the 2',7'-dichlorodihydrofluorescein diacetate (H₂DCFDA) staining to detect the effect of shikonin-ebselen on bacterial ROS production, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) to detect the effect of shikonin-ebselen on the thioredoxin reductase (TrxR) activity. Reactive oxygen species (ROS) was eliminated by adding ROS scavenger DL-dithiothreitol (DTT), and we further detected the relevant indicators. We isolated the multidrug resistant Staphylococcus aureus (MDRS) strains, and the antibacterial effects of shikonin-ebselen against MDRS were determined by spectrophotometry.[Results] We found shikonin and ebselen both have inhibitory effects on S. aureus, and 5 μmol/L shikonin and 10 μmol/L ebselen could work synergistically against bacteria (P<0.000 1). Shikonin-ebselen can significantly inhibit the activity of TrxR (P<0.01). Meanwhile, shikonin-ebselen can significantly induce the production of ROS in S. aureus (P<0.01). DTT can rescue the S. aureus from the shikonin-ebselen treatment. In addition, shikonin-ebselen also has a significant antibacterial effect on MDRS (P<0.000 1).[Conclusion] Shikonin-ebselen can execute antibacterial effect on S. aureus through inducing the production of a large amount of ROS by co-targeting the TrxR.