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J.Health Sci., 56(5), 618-622, 2010

-Research Letter-

Defensive Effects of Human Antimicrobial Peptide α-Defensins against Enterococcus faecalis

Shin-ichi Miyoshi,* Kenta Koyama, Tamaki Mizuno, Minoru Kashihara, Yoko Maehara, and Hiroshi Nakao

Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 1-1-1 Tushima-Naka, Okayama 700-8530, Japan

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.