Periodontitis is a chronic inflammatory disease caused by exaggerated host immune responses to dysregulated microbiota in dental biofilms leading to degradation of tissues and alveolar bone loss. Porphyromonas gingivalis is a major periodontal pathogen and expresses several potent virulence factors. Among these factors, arginine and lysine gingipains are of special importance, both for the bacterial survival/proliferation and the pathological outcome. The major aim of this thesis was to develop and test novel methods for diagnosis and prevention of P. gingivalis infection and periodontitis. In study I, anti-P. gingivalis antibodies were developed in vitro for immunodetection of bacteria in clinical samples using a surface plasmon resonance (SPR)-based biosensor. Specific binding of the antibodies to P. gingivalis was demonstrated in samples of patients with periodontitis and the results were validated using real-time PCR and DNA-DNA checkerboard analysis. In study II, we elucidated the properties and antimicrobial effects of different lactobacillus species and the two-peptide bacteriocin PLNC8 αβ on P. gingivalis. L. plantarum NC8 and 44048 effectively inhibited P. gingivalis growth and pure PLNC8 αβ induced bacterial lysis by damaging P. gingivalis membrane. In study III, we demonstrated that PLNC8 αβ dose-dependently induces proliferation and release of growth factors in gingival epithelial cells (GECs). Furthermore, PLNC8 αβ decreased P. gingivalis-induced cytotoxic effects in GECs but did not alter the effect of gingipains on cytokine expression. In study IV, we elucidated the effects of anti-P. gingivalis antibodies and PLNC8 αβ in regulating cellular responses during P. gingivalis infection. Both antibodies and PLNC8 αβ modulated P. gingivalis-induced expression of growth factors in GECs, however, their effects were diminished when used in combination. The results of this thesis demonstrate a possible role of anti-P. gingivalis antibodies and PLNC8 αβ in prevention and treatment of P. gingivalis infection and periodontitis with no cytotoxic effects on human cells.