The emergence of multidrug-resistant bacteria has major issues for treating bacterial pneumonia. Currently, anoplin (GLLKRIKTLL-NH 2 ) is a natural antimicrobial candidate derived from wasp venom. In this study, a series of new antimicrobial peptide (AMP) anoplin analogues were designed and synthesized. The relationship between their biological activities and their positive charge, hydrophobicity, amphipathicity, and secondary structure are described. The characteristic shared by these peptides is that positively charged amino acids and hydrophobic amino acids are severally arranged on the hydrophilic and hydrophobic surface of the α-helix to form a completely amphiphilic structure. To achieve ideal AMPs, below the range of the threshold of the cytotoxicity and hemolytic activity, their charges and hydrophobicity were increased as much. Among the new analogues, A-21 (KWWKKWKKWW-NH 2 ) exhibited the greatest antimicrobial activity (geometric mean of minimum inhibitory concentrations = 4.76 μM) against all the tested bacterial strains, high bacterial cell selectivity in vitro, high effectiveness against bacterial pneumonia in mice infected with Klebsiella pneumoniae, and low toxicity in mice (LD 50 = 82.01 mg/kg). A-21 exhibited a potent bacterial membrane-damaging mechanism and lipopolysaccharide-binding ability. These data provide evidence that A-21 is a promising antimicrobial candidate for the treatment of bacterial pneumonia.

The emergence of multidrug-resistant bacteria has dramatically increased the lethality, level of resistance, and difficulty of treatment. In this study, a series of new antimicrobial peptides (AMPs) based on the β-hairpin structure with the template (XY) 2 RRRF(YX) 2 -NH 2 (X: hydrophobic amino acids; Y: cationic amino acids) were synthesized; surprisingly, almost all of the new peptides have strong antibacterial activity and negligible hemolytic toxicity. Particularly, the therapeutic index (TI) values of F(RI)2R and F(KW)2K reached up to 115.9 and 70.7, respectively. In addition, they did not show induced drug resistance and inhibited the development of antibiotic resistance when combined and used with traditional antibiotics. In addition, their antibacterial mechanism was preliminarily studied. Moreover, the new peptides F(RI)2R and F(KW)2K showed excellent performance in the pulmonary bacterial infection model and low toxicity in mice. In conclusion, F(RI)2R and F(KW)2K are considered new antimicrobial alternatives to address the antimicrobial-resistance crisis.

Nonselective toxicity of antimicrobial peptides (AMPs) needs to be solved urgently for their application. Temporin-PE (T-PE, FLPIVAKLLSGLL-NH 2 ), an AMP extracted from skin secretions of frogs, has high toxicity and specific antimicrobial activity against Gram-positive bacteria. To improve the antimicrobial performance of T-PE, a series of T-PE analogues were designed and synthesized by glutamic acid full-scan, and then their key positions were replaced with lysine. Finally, E 11 K 4 K 10 , the highest therapeutic indicial AMP, was screened out. E 11 K 4 K 10 was not easy to induce and produce drug-resistant bacteria when used alone, as well as it could also inhibit the development of the drug resistance of traditional antibiotics when it was used in combination with the traditional antibiotics. In addition, E 11 K 4 K 10 had an excellent therapeutic effect on a mouse model of pulmonary bacterial infection. Taken together, this study provides a new approach for the further improvement of new antimicrobial peptides against the antimicrobial-resistance crisis.