Phenotypic Characterization of Porphyromonas gulae Fimbria Mutants

Porphyromonas gulae has been established as a pathogen in animal periodontal disease and expresses several virulence factors, including fimbriae, lipopolysaccharide, and proteases. P. gulae fimbriae are classified into three genotypes (A, B, and C) based on the fimbrillin (fimA) gene encoding a fimbrial subunit protein. We previously reported that P. gulae organisms with type C fimbriae were clearly more virulent as compared to those with other fimbria types, though the basic function of this is not fully understood. Here, we investigated the function of fimbriae using fimA-deficient mutants. In the present study, bacterial fimbriae were related to biofilm tenacity, whereas biofilm formation was not. Also, P. gulae fimbriae are involved in bacterial adhesion and entry into gingival epithelial cells. The role of P. gulae fimbriae in bacterial pathogenicity was then determined using fimA-deficient mutants with a silkworm infection model. Additionally, P. gulae infection can induce inflammatory responses in gingival epithelial cells and also inhibit cell migration and proliferation. In contrast, a P. gulae fimA-deficient mutant did not cause several of those cellular responses. Together, the results show that fimbriae contribute to the pathogenicity of P. gulae by affecting bacterial functions and host cell interactions.