An amphipathic and cationic antimicrobial peptide kills colistin resistant Gram-negative pathogens in vivo

New antibiotics are needed against multidrug resistant Gram-negative pathogens that have compromised global health systems. Antimicrobial peptides are generally considered promising lead candidates for the next generation of antibiotics but have not fulfilled this expectation. Here we demonstrate activity of a cationic amphipathic undecapeptide (ChIP; Charge change Independent Peptide) against a wide panel of multidrug resistant Gram-negative pathogens. Importantly, the antimicrobial activity of ChIP is independent of the surface charge changes that confer colistin resistance through modification of Lipid A, while decreased activity of ChIP correlates with GlcN1 tri-acylation of Lipid A. In an in vivo peritonitis mouse model ChIP displays excellent activity against both colistin sensitive and resistant Escherichia coli and Acinetobacter baumannii strains. Author Summary Antimicrobial peptides hold promise as novel treatment options for diseases caused by multidrug resistant bacteria. Here we present evidence that the ChIP peptide, comprised of 11 D-amino acids, is active against a variety of Gram-negative bacteria that ranks high on the WHO list of critically important pathogens. ChIP initially interacts with the Gram-negative outer membrane, independent of its surface charge, followed by entry into the periplasm and permeabilization of the inner membrane, leading to bacterial cell death. Detailed analyses of the outer membrane indicate that the acylation pattern of lipopolysaccharides plays an important role for ChIP activity. In a mouse infection model, ChIP display excellent activity in reducing bacterial numbers for both Escherichia coli and Acinetobacter baumannii . Importantly, ChIP is highly efficient against bacteria resistant to colistin, an antibiotic normally considered as a last resort treatment of infections caused by multidrug resistant Gram-negative bacteria. ### Competing Interest Statement The authors have declared no competing interest.