熊果酸与夫西地酸联用对金黄色葡萄球菌的协同抗菌作用

目的：探讨熊果酸（ursolic acid, UA）与夫西地酸（Fusidic acid, FA）联用对金黄色葡萄球菌（SA）ATCC29213、耐甲氧西林金黄色葡萄球菌（MRSA）ATCC43300的体外抗菌活性及潜在机制。方法：用微量肉汤稀释法、微量棋盘法测定UA与FA联用对SA、MRSA的最小抑菌浓度（MIC），计算部分抑菌浓度指数（FICI），判断联合效应。用时间杀菌曲线法判断UA联合FA的杀菌效果。采用琼脂二倍稀释法测定FA单用及联用UA时的防耐药突变浓度（MPC）和防耐药突变选择窗（MSW）。结晶紫染色法半定量生物膜，连续稀释法测定生物膜内活菌数。结果：UA和FA联用对SA、MRSA FICI分别为0.312 5、0.375。时间杀菌曲线显示，1MIC UA联合1MIC FA组对SA、MRSA有协同杀菌效应。FA对MRSA的MPC为256 μg/mL，联合UA后，MPC下降至8 μg/mL，MPC较单用降低32倍。UA联用FA组生物膜培养48 h和72 h后结晶紫半定量及生物膜内活菌数均较单用FA组明显降低。 结论：UA与FA联用对SA、MRSA具有协同作用。

Synergistic antibacterial effect of ursolic acid combined with fusidic acid on Staphylococcus aureus

AIM: To explore the antibacterial activity and underlying mechanism of ursolic acid combined with fusidic acid against Staphylococcus aureus (SA) ATCC29213 and Methicillin-Resistant Staphylococcus aureus (MRSA) ATCC43300 in vitro. METHODS: The minimum inhibitory concentration (MIC) of the combined use of ursolic acid and fusidic acid on SA, MRSA was determined by the micro broth dilution method and the micro checkerboard method, and the partial inhibitory concentration index (FICI) was calculated to determine the combined effect. And the bactericidal effect of fusidic acid combined with ursolic acid was studied by the time-killing curves. The agar double dilution method was used to determine the anti-drug resistance mutation concentration (MPC) and anti-drug resistance mutation selection window (MSW) of fusidic acid alone and in combination with ursolic acid. The viable count of biofilm carrier were determined by serial dilution method and the semi-quantitative biofilm by crystal violet staining method. RESULTS: The combined use of ursolic acid and fusidic acid for SA and MRSA FICI were 0.312 5 and 0.375, respectively. The time-killing curve showed that 1MIC ursolic acid combined with 1MIC fusidic acid has a synergistic bactericidal effect on SA and MRSA. The MPC of fusidic acid to MRSA was 256 μg/mL and the MSW was 256. After fusidic acid combined with ursolic acid, the MPC decreased to 8 μg/mL. The combined group was significantly reduced compared to the fusidic acid group. The semi-quantitative and biofilm bacterial counts of combined group were markedly decreased compared to the fusidic acid group after the biofilm cultivate for 48 h and 72 h.CONCLUSION: The combined use of UA and FA has a synergistic effect on SA and MRSA.