Abstract：
BACKGROUND: The emergence and spread of vancomycin-resistant enterococci (VRE) have posed a significant challenge to clinical treatment, underscoring the need to develop novel strategies. As therapeutic options for VRE are limited, discovering vancomycin enhancer is a feasible way of combating VRE. Gambogic acid (GA) is a natural product derived from the resin of Garcinia hanburyi Hook.f. (Clusiaceae), which possesses antibacterial activity.
OBJECTIVE: This study aimed to investigate the potential of GA as an adjuvant to restore the susceptibility of VRE to vancomycin.
METHODS: In vitro antibacterial and synergistic activities were evaluated against vancomycin-susceptible and resistant strains by the broth microdilution method for the Minimal Inhibitory Concentrations (MICs) determination, and checkerboard assay and time-kill curve analysis for synergy evaluation. In vivo study was conducted on a mouse multi-organ infection model. The underlying antibacterial mechanism of GA was also explored.
RESULTS: GA showed a potent in vitro activity against all tested strains, with MICs ranging from 2 to 4 μg/ml. The combination of GA and vancomycin exhibited a synergistic effect against 18 out of 23 tested VRE strains, with a median fractional inhibitory concentration index (FICI) of 0.254, and demonstrated a synergistic effect in the time-kill assay. The combination therapy exhibited a significant reduction in tissue bacterial load compared with either compound used alone. GA strongly binds to the ParE subunit of topoisomerase IV, a bacterial type II DNA topoisomerase, and suppresses its activity.
CONCLUSIONS: The study suggests that GA has a significant antibacterial activity against enterococci, and sub-MIC concentrations of GA can restore the activity of vancomycin against VRE in vitro and in vivo. These findings indicate that GA has the potential to be a new antibacterial adjuvant to vancomycin in the treatment of infections caused by VRE.
OBJECTIVE: This study aimed to investigate the potential of GA as an adjuvant to restore the susceptibility of VRE to vancomycin.
METHODS: In vitro antibacterial and synergistic activities were evaluated against vancomycin-susceptible and resistant strains by the broth microdilution method for the Minimal Inhibitory Concentrations (MICs) determination, and checkerboard assay and time-kill curve analysis for synergy evaluation. In vivo study was conducted on a mouse multi-organ infection model. The underlying antibacterial mechanism of GA was also explored.
RESULTS: GA showed a potent in vitro activity against all tested strains, with MICs ranging from 2 to 4 μg/ml. The combination of GA and vancomycin exhibited a synergistic effect against 18 out of 23 tested VRE strains, with a median fractional inhibitory concentration index (FICI) of 0.254, and demonstrated a synergistic effect in the time-kill assay. The combination therapy exhibited a significant reduction in tissue bacterial load compared with either compound used alone. GA strongly binds to the ParE subunit of topoisomerase IV, a bacterial type II DNA topoisomerase, and suppresses its activity.
CONCLUSIONS: The study suggests that GA has a significant antibacterial activity against enterococci, and sub-MIC concentrations of GA can restore the activity of vancomycin against VRE in vitro and in vivo. These findings indicate that GA has the potential to be a new antibacterial adjuvant to vancomycin in the treatment of infections caused by VRE.
摘要：
背景：耐万古霉素肠球菌（VRE）的出现和传播对临床治疗提出了重大挑战，强调了开发新战略的必要性。由于VRE的治疗选择有限，发现万古霉素增强剂是对抗VRE的可行途径。藤黄酸（GA）是一种天然产物，来自藤黄（Clusiaceae）的树脂，具有抗菌活性。
目的：本研究旨在探讨GA作为佐剂恢复VRE对万古霉素敏感性的潜力。
方法：通过肉汤微量稀释法对万古霉素敏感和耐药菌株的体外抗菌和协同活性进行了最低抑制浓度（MIC）测定，以及棋盘测定和时间杀伤曲线分析，用于协同评价。在小鼠多器官感染模型上进行体内研究。还探讨了GA的潜在抗菌机制。
结果：GA对所有测试菌株显示出有效的体外活性，MIC范围为2至4μg/ml。GA和万古霉素的组合对23种测试的VRE菌株中的18种表现出协同作用。中位分数抑制浓度指数（FICI）为0.254，并在时间杀伤试验中表现出协同作用。与单独使用的任一化合物相比,组合疗法表现出组织细菌负荷的显著减少。GA与拓扑异构酶IV的ParE亚基强烈结合，细菌II型DNA拓扑异构酶，并抑制其活动。
结论：研究表明，GA对肠球菌具有显著的抗菌活性，亚MIC浓度的GA可以在体外和体内恢复万古霉素对VRE的活性。这些发现表明，GA有可能成为万古霉素治疗VRE引起的感染的新的抗菌佐剂。
目的：本研究旨在探讨GA作为佐剂恢复VRE对万古霉素敏感性的潜力。
方法：通过肉汤微量稀释法对万古霉素敏感和耐药菌株的体外抗菌和协同活性进行了最低抑制浓度（MIC）测定，以及棋盘测定和时间杀伤曲线分析，用于协同评价。在小鼠多器官感染模型上进行体内研究。还探讨了GA的潜在抗菌机制。
结果：GA对所有测试菌株显示出有效的体外活性，MIC范围为2至4μg/ml。GA和万古霉素的组合对23种测试的VRE菌株中的18种表现出协同作用。中位分数抑制浓度指数（FICI）为0.254，并在时间杀伤试验中表现出协同作用。与单独使用的任一化合物相比,组合疗法表现出组织细菌负荷的显著减少。GA与拓扑异构酶IV的ParE亚基强烈结合，细菌II型DNA拓扑异构酶，并抑制其活动。
结论：研究表明，GA对肠球菌具有显著的抗菌活性，亚MIC浓度的GA可以在体外和体内恢复万古霉素对VRE的活性。这些发现表明，GA有可能成为万古霉素治疗VRE引起的感染的新的抗菌佐剂。
