Overexpression of NorA efflux pumps plays a pivotal role in the multidrug-resistance mechanism in S. aureus. Here, we investigated the activities of prenylated isoflavonoids, present in the legume plant family (Fabaceae), as natural efflux pump inhibitors (EPIs) in fluoroquinolone-resistant S. aureus. We found that four prenylated isoflavonoids, namely neobavaisoflavone, glabrene, glyceollin I, and glyceollin III, showed efflux pump inhibition in the norA overexpressing S. aureus. At sub-inhibitory concentrations, neobavaisoflavone (6.25 µg/mL, 19 µM) and glabrene (12.5 µg/mL, 39 µM), showed up to 6 times more Eth accumulation in norA overexpressing S. aureus than in the control. In addition, these two compounds boosted the MIC of fluoroquinolones up to eightfold. No fluoroquinolone potentiation was observed with these isoflavonoids in the norA knockout strain, indicating NorA as the main target of these potential EPIs. In comparison to the reported NorA EPI reserpine, neobavaisoflavone showed similar potentiation of fluoroquinolone activity at 10 µM, higher Eth accumulation, and less cytotoxicity. Neobavaisoflavone and glabrene did not exhibit membrane permeabilization effects or cytotoxicity on Caco-2 cells. In conclusion, our findings suggest that the prenylated isoflavonoids neobavaisoflavone and glabrene are promising phytochemicals that could be developed as antimicrobials and resistance-modifying agents to treat fluoroquinolone-resistant S. aureus strains.

NorA外排泵的过度表达在金黄色葡萄球菌的多重耐药机制中发挥着关键作用。在这里，我们研究了存在于豆科植物（豆科）中的异黄酮类化合物作为耐氟喹诺酮金黄色葡萄球菌的天然外排泵抑制剂（EPIs）的活性。我们发现四种异戊二烯化异黄酮类化合物，即新bavaisoflavone、glabrene、glyceollin I和glyceollin III，在norA过表达的金黄色葡萄球菌中表现出外排泵抑制作用。在亚抑制浓度下，在NorA过表达的金黄色葡萄球菌中，新巴伐利亚异黄酮 (6.25 µg/mL，19 µM) 和光甘草烯 (12.5 µg/mL，39 µM) 的 Eth 积累量比对照高出 6 倍。此外，这两种化合物将氟喹诺酮类药物的 MIC 提高了八倍。在norA敲除菌株中，没有观察到这些异黄酮类化合物对氟喹诺酮类药物有增强作用，表明NorA是这些潜在EPIs的主要靶标。与报道的 NorA EPI 利血平相比，新巴伐利亚异黄酮在 10 µM 时表现出类似的氟喹诺酮活性增强作用、更高的 Eth 积累和更低的细胞毒性。新bavaisoflavone 和glabrene 对Caco-2 细胞没有表现出膜透化作用或细胞毒性。总之，我们的研究结果表明，异戊二烯化异黄酮类新bavaisoflavone和glabrene是有前途的植物化学物质，可以开发作为抗菌剂和耐药性调节剂来治疗耐氟喹诺酮类金黄色葡萄球菌菌株。