Defensive effects of human antimicrobial peptide α-defensins against Enterococcus faecalis

Cationic and amphiphilic antimicrobial peptides (AMPs) such as α-defensins and cathelicidins are factors related to innate immunity. In the present study, we examined the protective effects of two AMPs, human neutrophil peptide-3 and α-defensin-5, against the opportunistic pathogen Enterococcus faecalis (E. faecalis). The α-defensins had dose-dependent bactericidal activity, whereas they showed no synergistic effect on the antimicrobial actions of antibiotics. Although AMPs often neutralize bacterial bioactive products, neither α-defensin reduced the proteolytic activity of GelE, a toxic protease from E. faecalis. On the other hand, the α-defensins were found to be fairly stable even in the presence of excess amounts of GelE. These results indicate that α-defensins may be defensive factors against E. faecalis in humans.