Newly designed antimicrobial peptides with potent bioactivity and enhanced cell selectivity prevent and reverse rifampin resistance in Gram-negative bacteria.

The increasing prevalence of antibiotic resistance in Gram-negative bacteria calls for the discovery of novel effective therapeutic strategies urgently. Mastoparan-C (MP-C), a typical cationic α-helical antimicrobial peptide, possesses remarkable broad-spectrum antimicrobial activity. However, its high cytotoxicity toward normal mammalian cells precludes it for further development. In this study, to avoid non-specific membrane lysis and investigate the structure-function relationships of each amino acid of MP-C, a series of new MP-C analogs were rationally designed by amino acid substitution and peptide truncation. Three potential newly designed peptides L1G, L7A, and L1GA5K with excellent bioactivity, modest cell toxicity, low resistance tendency, and moderate stability to physiological salts and proteases were screened out. Moreover, the newly designed peptides showed synergy or additive effects against Gram-negative bacteria, when they combined with conventional antibiotics gentamicin, rifampin, and polymyxin B. The results from the time-kill kinetics, outer/inner membrane permeabilization, scanning electron microscope (SEM), and flow cytometry demonstrated that the newly designed peptides could kill bacteria rapidly by membrane destruction and intracellular contents leakage in a concentration and time-dependent manner. Specifically, the most cell-selective peptide L1GA5K exhibited potent antimicrobial activity against rifampin-resistant E. coli (RRE) and prevented the emergence of rifampin resistance in Enterobacter. Besides, L1GA5K was capable of reversing rifampin resistance in RRE through the outer membrane permeabilization when used in combination with rifampin. Collectively, our results suggested that the newly designed peptides are hopeful antibiotic alternatives, and the usage of them as an adjuvant to prevent and reverse antibiotic resistance is a promising strategy for tackling the risk of drug-resistant Gram-negative bacteria.