Sensitization of gram-negative bacteria by targeting the membrane potential

Toward generating new tools for fighting multidrug-resistant (MDR) bacteria, we assessed the ability of a membrane-active peptide to sensitize gramnegative bacteria to various antibiotics. The mechanism for affecting inner and/or outer membrane functions was assessed by complementary biophysical methods (SPR, DSC, ITC). The implication of efflux pumps was examined using Acr-AB mutants, as tested with representative antibiotics, host defense peptides, and synthetic mimics. The ability to affect disease course systemically was compared for a single therapy and combination therapy, using the mouse thigh-infection model. The data show that potent antibiotic action can be provoked in vitro and in vivo, by a treatment combining two antibacterial compounds whose individual inefficiency against gramnegative bacteria stems from their efflux. Thus, at subminimal inhibitory concentrations, the lipopeptide-like sequence, N^α(ω7)dodecenoyl-lysyl-[lysyl- aminododecanoyl- lysyl]-amide (designated C_12(ω7)K- β₁₂), has, nonetheless, rapidly achieved a transient membrane depolarization, which deprived bacteria of the proton-motive force required for active efflux. Consequently, bacteria became significantly sensitive to intracellular targeting antibiotics. Collectively, these findings suggest a potentially useful approach for expanding the antibiotics sensitivity spectrum of MDR gram-negative bacteria to include efflux substrates.-Goldberg, K., Sarig, H., Zaknoon, F., Epand, R. F., Epand, R. M., Mor, A. Sensitization of gram-negative bacteria by targeting the membrane potential.