Antimicrobial and antibiofilm activities of ursolic acid against carbapenem-resistant Klebsiella pneumoniae.

Previous studies demonstrated that ursolic acid (UA) present in apple pomace displays antimicrobial activity against some microorganisms, but the underlying mechanisms associated with this activity remain unexplored. Furthermore, there are no reports on the effect of UA on carbapenem-resistant Klebsiella pneumoniae (CRKP). This study examined the antimicrobial activity and mode of action of UA against CRKP was examined. Minimum inhibitory concentration (MIC) of UA against CRKP was determined by the agar dilution method. Variations in the intracellular pH (pHin), ATP concentration, and cell membrane potential were measured to assess the influence of UA on the cell membrane. Our results show that UA was effective against CRKP at an MIC of 0.8 mg ml-1. UA disrupted the cell membrane integrity of CRKP, exhibited strong inhibitory effects against biofilm formation and biofilm-related gene expression, and inactivated CRKP cells encased in biofilms. Thus, UA shows promise for use in combination with other antibiotics to treat multidrug resistant K. pneumoniae infections.