Mechanisms of envelope permeability and antibiotic influx and efflux in Gram-negative bacteria

Researchers, clinicians and governments all recognize antimicrobial resistance as a serious and growing threat worldwide. New antimicrobials are urgently needed, especially for infections caused by Gram-negative bacteria, whose cell envelopes are characterized by low permeability and often contain drug efflux systems. Individual bacteria and populations control their internal concentrations of antibiotics by regulating proteins involved in membrane permeability, such as porins or efflux pumps. Robust methods to quantify and visualize intrabacterial antibiotic concentrations have identified clear correlations between efflux activity and drug diffusion and accumulation in both susceptible and resistant strains, and have also clarified how certain chemical structures can affect drug entry and residence time within the cell. In this PERSPECTIVE, we discuss the biological underpinnings of drug permeability and export using several prototypical influx and efflux systems. We also highlight how new methods for the determination of antibacterial activities enable more careful quantitation and may provide us with a way forward for capturing and correlating the modes of action and kinetics of antibiotic uptake inside bacterial cells. Together, these advances will aid efforts to generate structurally improved molecules with better access and retention within bacteria, thereby reducing the emergence and spread of resistant strains and extending the clinical use of current antibiotics. A Perspective on unravelling the mechanisms of antibiotic penetration and efflux in Gram-negative bacteria.