ABSTRACT. Porphyromonas gulae, a gram-negative black-pigmented anaerobe, is a pathogen for periodontitis in dogs. An approximately 41-kDa fimbrial subunit protein (FimA) encoded by fimA is regarded as associated with periodontitis. In the present study, the fimA genes of 17 P. gulae strains were sequenced, and classified into two major types. The generation of phylogenetic trees based on the deduced amino acid sequence of FimA of P. gulae strains along with sequences from several strains of Porphyromonas gingivalis, a major cause of human periodontitis, revealed that the two types of FimA (types A and B) of P. gulae were similar to type I FimA and types II and III FimA of P. gingivalis, respectively. A PCR system for classification was established based on differences in the nucleotide sequences of the fimA genes. Analysis of 115 P. gulae-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 fimA genes, respectively. Experiments with a mouse abscess model demonstrated that the strains with type B fimA caused significantly greater systemic inflammation than those with type A. These results suggest that the FimA proteins of P. gulae are diverse with two major types and that strains with type B fimA could be more virulent. Periodontal diseases are characterized by gingivitis, a reversible condition involving gingival inflammation, and periodontitis, the irreversible destruction of periodontal tissues such as cementum, periodontal ligaments, and supportive bone [15]. In dogs, the prevalence of gingivitis is 95-100% and that of periodontitis, 50-70%, and the severity of periodontal disease tends to worsen with age, as in humans [8,10].Numerous periodontitis-related bacterial species have been reported in humans, with Porphyromonas gingivalis, a gram-negative black-pigmented anaerobe, considered a major species [15]. The 41-kDa cell surface protein fimbrillin (FimA), a subunit of fimbriae, is an important virulence factor of periodontitis, associated with adhesion to and invasion of gingival cells [4]. There are six genotypes of fimA encoding FimA (I through V and Ib), among which types II/ IV/Ib and I/III/V are considered invasive and non-invasive, respectively [2,3,[11][12][13][14]17].A previous analysis of 11 periodontitis-related bacterial species in oral swab specimens collected from 26 pet dogs in Japan showed that the isolation frequency of P. gingivalis was extremely low in dogs [9]. In contrast, Porphyromonas gulae was frequently detected in these specimens, accounting for approximately 70% of all Porphyromonas isolates. A recent study revealed the presence of a 41-kDa FimA, similar to that in P. gingivalis, in P. gulae [7]. In the present study, we performed molecular analyses of fimA in many clinical strains of P. gulae focusing on the association between the gene's diversity and virulence. Table 1 lists the P. gulae strains analyzed in the present study, 10 of which were isolated in Tokyo, Japan, previously [9]. The 7 new clinic...
