The anaerobic bacterium Porphyromonas gingivalis, a major pathogen in
periodontitis, aggregates with a number of oral bacteria to form
dental plaque, which is important for its colonization. We previously cloned the gene coding the 40-kDa outer
membrane protein (OMP) of P. gingivalis 381 and produced large amounts of the recombinant (r)
protein. Affinity-purified rabbit antiserum against r40-kDa OMP effectively inhibited the coaggregation activity of P. gingivalis to oral bacteria, thus 40-kDa OMP was thought to be an important coaggregation factor of P. gingivalis. Further, since it is conserved among many P. gingivalis strains, this coaggregation factor may be an effective target for passive immunotherapy against P. gingivalis
infection. Recently, passive immunization approaches using a specific antibody produced from hen egg yolk (
IgY) have been developed for oral
infectious diseases, and shown to be convenient and economic. In the present study, we immunized hens intramuscularly with r40-kDa OMP and obtained highly purified
IgY from the egg yolks. The purified
IgY specifically recognized r40-kDa OMP and also reacted with a functional coaggregation-associated domain peptide of 40-kDa OMP. Our results demonstrated that a ratio of purified
IgY as low as 2.5 microg/150 microl significantly inhibited the coaggregation of P. gingivalis with Streptococcus gordonii, which was verified by a visual coaggregation assay and radioactivity-based quantitative micro-coaggregation assay. We concluded anti-r40-kDa OMP
IgY may be useful for passive immunization against
periodontal diseases caused by P. gingivalis
infection.