Antibacterial Activity of Licochalcone A against Spore-Forming Bacteria

Licochalcone A was isolated from the roots of licorice, Glycyrrhiza inflata, which has various uses in the food and pharmaceutical industries; isolation was followed by extraction with ethanol and column chromatography with silica gel. In this study, the activities of licochalcone A against some food contaminant microorganisms were evaluated in vitro. The vegetative cell growth of Bacillus subtilis was inhibited in a licochalcone A concentration-dependent manner and was completely prevented by 3 μg of licochalcone A/ml. Licochalcone A showed a high level of resistance to heating at 80 to 121°C for 15 min. Licochalcone A did not inhibit the germination of heat-treated spores of B. subtilis induced by l-alanine. Licochalcone A showed effects against all gram-positive bacteria tested and especially was effective against all Bacillus spp. tested, with MICs of 2 to 3 μg/ml, but was not effective against gram-negative bacteria or eukaryotes at 50 μg/ml. Although the cationic antimicrobial peptides protamine and ɛ-poly-l-lysine resulted in the loss of antimicrobial activity in the presence of either 3% (wt/vol) NaCl or protease at 20 μg/ml, the antibacterial activity of licochalcone A was resistant to these conditions. Thus, licochalcone A could be a useful compound for the development of antibacterial agents for the preservation of foods containing high concentrations of salts and proteases, in which cationic peptides might be less effective.

甘草查尔酮A（Licochalcone A）提取自胀果甘草（Glycyrrhiza inflata）的根部，该物质在食品与医药工业中具有多种应用价值；其分离流程为先采用乙醇萃取，再通过硅胶柱色谱法完成纯化。本研究针对甘草查尔酮A对若干食品污染微生物的抗菌活性开展了体外评价。枯草芽孢杆菌（Bacillus subtilis）的营养体细胞生长呈现甘草查尔酮A浓度依赖性抑制效应，当甘草查尔酮A浓度达到3 μg/ml时可完全阻断其生长。甘草查尔酮A对80℃至121℃、时长15分钟的加热处理具有极佳的耐受性。甘草查尔酮A无法抑制经热处理的枯草芽孢杆菌孢子在L-丙氨酸（L-alanine）诱导下的萌发过程。甘草查尔酮A对所有受试革兰氏阳性菌均表现出抗菌活性，尤其对所有受试芽孢杆菌属（Bacillus spp.）菌株具有显著抑制效果，其最低抑菌浓度（MIC）范围为2~3 μg/ml；但当浓度达到50 μg/ml时，该物质对革兰氏阴性菌及真核生物均无抑制作用。尽管阳离子抗菌肽鱼精蛋白（protamine）和ε-聚-L-赖氨酸（ɛ-poly-L-lysine）在3%（质量体积比，wt/vol）氯化钠或20 μg/ml蛋白酶存在的条件下会丧失抗菌活性，但甘草查尔酮A的抗菌活性可耐受上述两种环境条件。因此，甘草查尔酮A可作为一种极具应用潜力的化合物，用于开发抗菌保鲜剂，以应用于高盐及富含蛋白酶的食品保鲜场景——此类场景中阳离子抗菌肽往往难以发挥预期效果。