Mode of the Interaction of Efflux Inhibitor Phenylalanyl-arginyl-β-naphtylamide with Bacterial Cells

An increased efflux activity is one of the major reasons for bacterial antibiotic resistance. The usage of efflux pump inhibitors could be a promising approach to restoring the activity of inefficient antibiotics. The interaction of the RND family efflux pump inhibitor phenylalanyl-arginyl-β-naphthylamide (PAβN) with Salmonella enterica ser. Typhimurium cells was assayed using traditional microbiological techniques and a novel PAβN-selective electrode. Monitoring the PAβN concentration in the medium using the electrode enabled the real-time measurements of this compound's interaction with bacterial cells. We showed that S. Typhimurium cells accumulate a high amount of PAβN because of its high affinity to lipopolysaccharides (LPSs), the major constituent of the outer layer of the outer membrane, and does not affect the functioning of the plasma membrane. EDTA enhanced the binding of PAβN to S. Typhimurium cells and the purified E. coli LPSs, but the energization of the cells by glucose does not affect the cell-bound amount of this inhibitor. Polycationic antibiotic Polymyxin B released both the cells accumulated and the suspended LPS-bound PAβN.