Diversity of Fimbrillin among <i>Porphyromonas gulae</i> Clinical Isolates from Japanese Dogs

<i>Porphyromonas gulae</i>, a gram-negative black-pigmented anaerobe, is a pathogen for periodontitis in dogs. An approximately 41-kDa fimbrial subunit protein (FimA) encoded by <i>fimA</i> is regarded as associated with periodontitis. In the present study, the <i>fimA</i> genes of 17 <i>P. gulae</i> strains were sequenced, and classified into two major types. The generation of phylogenetic trees based on the deduced amino acid sequence of FimA of <i>P. gulae</i> strains along with sequences from several strains of <i>Porphyromonas gingivalis,</i> a major cause of human periodontitis, revealed that the two types of FimA (types A and B) of <i>P. gulae</i> were similar to type I FimA and types II and III FimA of <i>P. gingivalis</i>, respectively. A PCR system for classification was established based on differences in the nucleotide sequences of the <i>fimA</i> genes. Analysis of 115 <i>P. gulae</i>-positive oral swab specimens from dogs revealed that 42.6%, 22.6%, and 26.1% of them contained type A, type B, and both type A and B <i>fimA</i> genes, respectively. Experiments with a mouse abscess model demonstrated that the strains with type B <i>fimA</i> caused significantly greater systemic inflammation than those with type A. These results suggest that the FimA proteins of <i>P. gulae</i> are diverse with two major types and that strains with type B <i>fimA</i> could be more virulent.