Killing of oral, gram-negative, facultative bacteria by the rabbit defensin, NP-1

Oral, gram-negative, facultative bacteria, including Actinobacillus actinomycetemcomitans, Eikenella corrodens, and Capnocytophaga spp. have been associated with destructive periodontal infection. Neutrophils play a critical role in defending the periodontium against destructive infection. Defensins are antimicrobial peptides that have been isolated in human, rabbit, guinea pig, and rat leukocytes that may constitute an important nonoxidative mechanism of killing. The purpose of this study was to examine the sensitivity of a battery of oral, gram-negative, facultative bacteria to the bactericidal effects of the isolated rabbit peptide NP-1. All species tested were killed by NP-1; however, there was strain-to-strain variation in sensitivity. The bactericidal effect was not dependent on net bacterial growth, although metabolic activity was evident as assessed by bacterial oxygen consumption. We conclude that bacteria are sensitive to the cidal mechanism involved in defensin-mediated bacterial killing and that the conditions of this assay system support the killing of bacteria by the defensin peptides.