A dextrorotatory residues-incorporated bioactive dodecapeptide against enterohemorrhagic Escherichia coli

Aim: This study aims to report an engineered peptide zp39 with favorable bioactivity against enterohemorrhagic Escherichia coli (E. coli, EHEC). Its antibacterial mechanisms and application in a real food system are assessed. Methods: Spatial conformation of synthetic peptide zp39 (GIIAGIIiKIKk-NH2, lowercase letters indicate dextrorotatory amino acids) was predicted by PEPstrMOD and its secondary structure was further determined by circular dichroism (CD) spectroscopy. Then, standard E. coli O157:H7 strain ATCC 43888 was used to evaluate the bioactivity of zp39. A double dilution method was applied to investigate its efficacy in normal broth medium, serum, and highly saline conditions. Its effects on cell membrane permeability and potential were measured by fluorescent assays. Thereafter, morphological changes of E. coli O157:H7 cells were monitored by electron microscopy technologies. Finally, the potential application of zp39 in controlling EHEC in food was tested with spinach juice and the Galleria mellonella larvae model was employed to assess the in vivo efficacy. Results: Peptide zp39 presented an amphiphilic helical structure. It effectively inhibited the growth of E. coli O157:H7 at a concentration of 4 μmol/L in a bactericidal mode. Mechanistic studies revealed that it affected membrane permeability and potential in a dose-dependent manner. Moreover, zp39 maintained satisfactory bioactivity against E. coli O157:H7 even in the presence of 70% serum or 1,000 μmol/L chloride salts. In spinach juice application, > 90% E. coli O157:H7 cells were killed within 2 h after exposure to 64 μmol/L zp39. In vivo study proved that treatment with 64 μmol/L zp39 could effectively boost the survival ratio of infected larvae by 50%. Conclusions: This study depicts a synthetic dodecapeptide that shows the potential application in controlling EHEC. This molecule may be developed into a highly effective antimicrobial agent applied to prevent food contamination and associated infections.