Suppression of the Rhizoma Coptidis-Mediated Antibiotic Cross-Resistance in Staphylococcus aureus Using Radix Paeoniae Rubra.

This study aimed to investigate the underlying mechanism of action and further identify main active ingredient by which Radix Paeoniae Rubra extracts (RPRE) inhibited the cross-resistance to tetracycline (TET), piperacillin (PIP), and gentamicin (GEN) mediated by Rhizoma Coptidis extracts (RCE) in Staphylococcus aureus (SA). Treatment with mixed solutions of RCE and RPRE resulted in disappearance of TET, PIP, or GEN resistance compared to what was shown with RCE treatment alone. Fifteen relevant resistant genes (smrB, bmr3, nhoA, BTN44_15030, clpL, hisG, norA, fmtA_1, emrB_1, BTN44_07590, paiA, icaR, BTN44_13995, HMPREF0776_1664 and vraG) were significantly downregulated compared to the RCE-induced mutants. RPRE was sequentially fractionated using macroporous resin and silica gel column chromatography, and all resulting eluates exhibited the antibacterial activity against Staphylococcus ATCC 25923. When exposed to RCE combined with either 30% EE or DCM:MeOH(5:1) eluates, no significant cross-resistance to the tested antibiotics was observed in the induced isolates. Similarly, the expression levels of the fifteen resistant genes were markedly reduced. Furthermore, gallic acid (GA) was identified in the two aforementioned eluates using HPLC-MS. After selection with a mixed solution of RCE and GA, the induced strains displayed no cross-resistance to the tested antibiotics, and the expression of the resistant genes was significantly decreased. These results suggest that GA is a key active ingredient in RPRE responsible for suppressing RCE-mediated cross-resistance to TET, PIP, and GEN in SA.