Recent studies demonstrate that ursolic acid (UA) presents potent antimicrobial activity against a few microorganisms, however, the underlying mechanisms remain elusive. Moreover, little is known about the effect of UA on carbapenem-resistant Enterobacter cloacae (CREC). In this study, we aimed to investigate the mechanisms underlying-antimicrobial activity of UA and its mode of action against CREC. Minimum inhibitory concentrations (MIC) of UA against CREC were determined by the agar dilution method. The antibacterial effect of UA against CREC was elucidated by evaluating changes in intracellular ATP concentration, intracellular pH, membrane potential, membrane integrity, and cell morphology. A crystal violet assay, field emission scanning electron microscopy (FESEM), and confocal laser scanning microscopy (CLSM) were applied to examine the effect of UA on biofilm formation. Furthermore, the inactivation of CREC cells in biofilms was explored by CLSM. Our results showed that UA has a MIC of 0.1 mg/mL against CREC. UA treatment inhibited CREC growth and impaired membrane integrity of CREC cells, as measured by the decrease in intracellular ATP level, pH, and membrane potential, as well as distinctive deformation in cellular morphology. Moreover, UA exerted a significant inhibitory effect on biofilm formation of CREC and inactivated CREC cells within biofilms. These findings reveal that UA has potent antibacterial and antibiofilm activity against CREC and, thus, can be used as a natural food preservative to reduce CREC-related infections.

最近的研究表明，熊果酸（UA）具有针对几种微生物的有效抗菌活性，但是，其潜在机制仍然难以捉摸。此外，关于UA对耐碳青霉烯的阴沟肠杆菌的影响了解甚少（CREC）。在这项研究中，我们旨在研究UA的潜在抗菌活性机制及其对CREC的作用方式。通过琼脂稀释法确定UA对CREC的最小抑制浓度（MIC）。通过评估细胞内ATP浓度，细胞内pH，膜电位，膜完整性和细胞形态的变化，阐明了UA对CREC的抗菌作用。结晶紫分析，场发射扫描电子显微镜（FESEM）和共聚焦激光扫描显微镜（CLSM）用于检查UA对生物膜形成的影响。此外，CLSM探索了生物膜中CREC细胞的失活。我们的结果表明，UA对CREC的MIC为0.1 mg / mL。UA治疗会抑制CREC生长并损害CREC细胞的膜完整性，通过细胞内ATP水平，pH和膜电位的降低以及细胞形态的明显变形来衡量。而且，UA对CREC的生物膜形成和生物膜内的失活的CREC细胞具有显着的抑制作用。这些发现表明，UA具有针对CREC的有效抗菌和抗生物膜活性，因此可以用作减少CREC相关感染的天然食品防腐剂。