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Antimicrobial resistance is a world-wide health care crisis. New antimicrobials must both exhibit potency and thwart the ability of bacteria to develop resistance to them. We report the use of synthetic ionophores as a new approach to developing non-resistant antimicrobials and adjuvants. Most studies involving amphiphilic antimicrobials have focused on either developing synthetic amphiphiles that show ion transport, or developing non-cytotoxic analogs of such peptidic amphiphiles as colistin. We have rationally designed, prepared, and evaluated crown ether-based synthetic ionophores (‘hydraphiles’) that show selective ion transport through bilayer membranes and are toxic to bacteria. We report here that hydraphiles exhibit a broad range of antimicrobial properties and that they function as adjuvants in concert with FDA-approved antibiotics against multi-drug resistant (MDR) bacteria. Studies described herein demonstrate that benzyl C 14 hydraphile (BC 14 H) shows high efficacy as an antimicrobial. BC 14 H, at sub-MIC concentrations, forms aggregates of ∼200 nm that interact with the surface of bacteria. Surface-active BC 14 H then localizes in the bacterial membranes, which increases their permeability. As a result, antibiotic influx into the bacterial cytosol increases in the presence of BC n Hs. Efflux pump inhibition and accumulation of substrate was also observed, likely due to disruption of the cation gradient. As a result, BC 14 H recovers the activity of norfloxacin by 128-fold against resistant Staphylococcus aureus . BC 14 H shows extremely low resistance development and is less cytotoxic than colistin. Overall, synthetic ionophores represent a new scaffold for developing efficient and non-resistant antimicrobial-adjuvants. 

Hydraphiles are synthetic amphiphiles that form pores in bilayer membranes. A study was undertaken to determine if the formation of pores could assist the penetration of antibiotics into bacteria. The disruption of ion homeostasis by the pore-formers leads to microbial toxicity. Co-administration of hydraphiles at concentration ≤ ½ MIC and antimicrobials to E. coli or P. aeruginosa showed potency enhancements of up to 30-fold. A possible mechanism is the enhancement of antibiotic influx owing to membrane disruption and/or altering the ion balance within the bacterial cells.