Objective To study the method of conversing the OmpA signal peptide of E. coli into antimicrobial peptide and its bactericidal activity. Methods The OmpA signal peptide （P-AQA） of E. Coli that consists of 21 amino acids was used as template, three derived peptides（MKKTAIAIAVALAGFARVRQK，P-RQK）、（MKKTAIAIAVALAGFARRKKK，P-KKK）、（MKKTAIAIAVALAGFAD VDQD，P-DQD）were synthesized by changing the amino acid composition of the Cterminal of the OmpA signal peptide of E. coli. The bactericidal activity of the three derived peptides against grampositive bacteria (G+) (Staphylococcus aureus) and gramnegative bacteria (G-) (Escherichia coli) was determined by agar plate counting method. Results The natural signal peptide PAQA was insoluble in water, the bactericidal activity could not determine; the peptide PDQD with acidic amino acid added at the Cterminal of the signal peptide had no bactericidal action on G+ and G-; the other two polypeptides with the basic amino acid at the terminal had strong bactericidal action to G+ and G- , and the bactericidal activity of the polypeptides with 5 basic amino acids at the terminal was about 5 times higher than that of 3 basic amino acids. Conclusions The derived peptide which neutral amino acid was replaced by basic amino acids in the Cterminal of the OmpA signal peptide of E. coli, with evident bactericidal activity, and the bactericidal activity might be correlated with the numbers of basic amino acids.

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