Porphyromonas gingivalis is a periodontal pathogen whose fimbriae are classified into six genotypes based on the diversity of the fimA genes encoding each fimbria subunit. It was suggested that P. gingivalis strains with type II fimbriae were more virulent than type I strains. For the present study, we generated the mutants in which fimA was substituted with different genotypes to study virulence of type II fimbriae. Using plasmid vectors, fimA of ATCC33277 (type I strain) was substituted with type II fimA, and that of OMZ314 (type II strain) with type I fimA. The substitution of type I fimA with type II enhanced bacterial adhesion/invasion to epithelial cells, whereas substitution with type I fimA resulted in diminished efficiency. Following bacterial invasion, type II clones swiftly degraded cellular paxillin and focal adhesion kinase, and inhibited cellular migration, whereas type I clones and ΔfimA mutants did not. BIAcore analysis demonstrated that type II fimbriae possess greater adhesive abilities for their receptor α5β1-integrin than those of type I. In a mouse abscess model, the type II clones significantly induced serum IL-1β and IL-6, as well as other infectious symptoms. These results suggest that type II fimbriae are a critical determinant of P. gingivalis virulence.
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