An enhancer peptide for membrane-disrupting antimicrobial peptides

Background: NP4P is a synthetic peptide derived from a natural, non-antimicrobial peptide fragment (pro-region of nematode cecropin P4) by substitution of all acidic amino acid residues with amides (i.e., Glu -> Gln, and Asp -> Asn). Results: In the presence of NP4P, some membrane-disrupting antimicrobial peptides (ASABF-alpha, polymyxin B, and nisin) killed microbes at lower concentration (e.g., 10 times lower minimum bactericidal concentration for ASABF-alpha against Staphylococcus aureus), whereas NP4P itself was not bactericidal and did not interfere with bacterial growth at <= 300 mu g/mL. In contrast, the activities of antimicrobial agents with a distinct mode of action (indolicidin, ampicillin, kanamycin, and enrofloxacin) were unaffected. Although the membrane-disrupting activity of NP4P was slight or undetectable, ASABF-alpha permeabilized S. aureus membranes with enhanced efficacy in the presence of NP4P. Conclusions: NP4P selectively enhanced the bactericidal activities of membrane-disrupting antimicrobial peptides by increasing the efficacy of membrane disruption against the cytoplasmic membrane.