Abstract:

Quercetin is a flavonoid compound with various biological activities， mostly existing in the form of glycosides in plants. Sophora japonica is an ideal raw material for preparing quercetin， with advantages such as wide planting area and low price.　This study investigated the synergistic antibacterial effects of quercetin against Salmonella spp. that combined with colistin. The quercetin was prepared from the Sophora japonica buds Aspergillus niger fermentation and isolated from the semi-solid fermentation products using ultrasonic extraction methods， purified and structurally identified using HPLC， ESI-MS and NMR methods. The antibacterial activities of quercetin and colistin， both individually and in combination， against Salmonella were evaluated using dilution and checkerboard methods. The results showed that the highest product of quercetin was 73.7 mg·g^-1 after fermentation for 96 h and the purity reached to 98% after purification and identification. After evaluation of antibacterial activity， the minimum inhibitory concentrations （MICs） of colistin against S. typhimurium， S. pullorum 1789 and 520 were 2， 8， and 4 μg·mL^-1， respectively， while the MICs of quercetin against the mentioned strains were all above 500 μg·mL^-1. When quercetin was used together with colistin， the synergistic antibacterial effects were observed against above Salmonella strains， particularly against S. pullorum 1789 and 520， with fractional inhibitory concentration index （FICI） values below 0.5， and the MIC value of colistin were reduced to 1 μg·mL^-1. The study demonstrated the synergistic inhibitory effect of quercetin prepared from Sophora japonica through A. niger fermentation combined with colistin against Salmonella， providing a scientific basis for developing new antibacterial combination strategies.

Key words: quercetin, Sophora japonica, Aspergillus niger, Salmonella, colistin, synergistic inhibition

摘要：

槲皮素是一种黄酮类化合物，具有多种生物活性，大多以糖苷类化合物形式存在植物中。槐米是一种理想的制备槲皮素的原料，具有种植面积广、价格低廉等优点。探讨了黑曲霉发酵槐米制备的槲皮素与粘杆菌素联合作用对沙门氏菌（Salmonella spp.）的抑制效果。通过黑曲霉与槐米的半固体发酵及超声提取方法，从发酵产物中提取槲皮素，采用HPLC和ESI-MS/NMR技术进行纯化和结构鉴定，并利用肉汤稀释法和棋盘格法评估了槲皮素与粘杆菌素对沙门氏菌的单独及联合抑制效果。结果表明，槲皮素含量在发酵96 h达到最高，为73.7 mg·g^-1。经提取、纯化和结构鉴定的槲皮素纯度≥98%。在抗菌活性评估中，粘杆菌素对鼠伤寒沙门氏菌（S. typhimurium）、鸡白痢沙门氏菌1789（S. pullorum 1789）和鸡白痢沙门氏菌520（S. pullorum 520）的最小抑菌质量浓度（minimal inhibitory concentration，MIC）分别为2、8和4 μg·mL^-1，而槲皮素对上述菌株的MIC均超过500 μg·mL^-1。制备的槲皮素与粘杆菌素联用时，对3株沙门氏菌均表现出联合抗菌效果，尤其对鸡白痢沙门氏菌1789和520，其分数抑制浓度指数（fractional inhibitory concentration index，FICI）值均低于0.5，并且粘杆菌素的MIC值在联用后均降为1 μg·mL^-1，表明槲皮素与粘杆菌素之间存在显著的协同抑制作用。研究结果证明了通过黑曲霉发酵槐米制备的槲皮素与粘杆菌素联合对沙门氏菌具有协同抑制作用，为开发新型抗菌组合策略提供了科学参考依据。

关键词: 槲皮素, 槐米, 黑曲霉, 粘杆菌素, 沙门氏菌, 协同抑制