Mechanisms of action of ostrich β-defensins against Escherichia coli

To understand their mechanism of antimicrobial activity against Gram-negative bacteria, ostrich beta-defensins, ostricacins-1 and 2 (Osp-1 and Osp-2), were compared with those of sheep myeloid antimicrobial peptide (SMAP)-29 and human neutrophil peptide (HNP)-1, well-characterized sheep alpha-helical and human alpha-defensin peptides, respectively. Fluorescence-based biochemical assays demonstrated that the ostricacins bound lipopolysaccharides and disrupted both outer and cytoplasmic membrane integrity. The ostricacins' permeabilizing ability was weaker than that of SMAP-29, but stronger than HNP-1. As ostricacins have previously shown the ability to inhibit bacterial growth, these peptides were suggested to be bacteriostatic to Gram-negative bacteria, which are caused by the interaction between the peptides and cytoplasmic targets causing the inhibition of DNA, RNA, and protein synthesis as well as enzymatic activities. These findings indicated promising possibilities for the peptides to be used in the development of therapeutic and topical products.