**4.5 Genus** *Fusobacterium*

*Bacterial Biofilms*

Representatives of this genus are Gram-negative, anaerobic, non-motile rods. The primary periodontal pathogen is *Tannerella forsythia* originally described as *Bacteroides forsythus*, and reclassified to *Tannerella forsythia* based on 16S rRNA phylogenetic analysis [54]. *T. forsythia* should be regarded as common member of oral microbiota in dogs [42], but dogs with gingivitis or periodontitis are more likely to be infected with *T. forsythia* than healthy animals [26]. *T. forsythia* has several virulence factors, including surface antigen BspA, cell surface proteolytic enzymes, hemagglutinin, cell envelope lipoproteins, glycosidases and cell surface (S)-layer, which contribute to pathogenic potential. The surface protein BspA can bind extracellular matrix components as well as other oral bacteria, and is partly

The genus *Campylobacter* is phylogenetically classified in the family

Campylobacteraceae, order *Campylobacterales*, class *Epsilonproteobacteria* and phylum *Proteobacteria*. Species *Campylobacter rectus* (formerly *Wolinella recta*), Gramnegative, microaerophilic and motile bacterium, is regarded as common member of oral microbiota in dogs. *C. rectus*, *Tannerella forsythia* and *Porphyromonas gulae* are three major species present in dogs with periodontitis base on study using molecular biological approaches [42]. Several possible factors of virulence have been described for *C. rectus*, such as flagellum, surface layer proteins (S-layer), RTX-type toxins, GroELlike proteins and lipopolysaccharide [56]. *C. rectus* may be an important indicator of periodontal disease. Together with other oral anaerobic bacteria, *C. rectus* is associated with the initiation and progression of periodontal

The genus *Treponema* is phylogenetically classified in the family *Spirochaetaceae*, order *Spirochaetales*, class *Spirochaetesa* and phylum *Spirochaetes*. *Treponemes* are Gram-negative, obligate anaerobic, motile spirochetes. *Treponemes* are involved in the development of chronic domestic animal diseases, including periodontal diseases in dogs [58]. Dogs harbor several different *Treponema* spp. in their oral cavity, and they can be common in both healthy and periodontitis affected dogs, indicating they are part of the normal oral microbiota [40]. Canine dental biofilm include species *T. denticola*, *T. socranskii*, *T. vincentii*, *T. maltophilum*, *T. medium* and *T. pectinovorum* [59]. Prevalence *T. denticola* and *T. socranskii* is significantly higher in dogs with periodontitis than in dogs without periodontitis. In addition, *Treponema* spp. are

not only in the microbial biofilm but also within the gingival tissue [60].

*Treponemes*, including *T. denticola*, are found on the surface of dense subgingival bacterial biofilms, particularly at the interface of biofilms and gingival epithelium. *T. denticola* has been shown to adhere to fibroblasts and epithelial cells as well as extracellular components of the matrix present in periodontal tissues, and produces several harmful factors that can contribute to virulence of bacteria [61]. The main virulence factors of *T. denticola* in chronic periodontitis include motility and chemotaxis, the ability to interact synergistically with other periodontal pathogens, the ability to produce cytotoxic metabolites, the ability to form biofilms and a variety of cell surface proteins. Motility and chemotaxis allow the bacterium to rapidly colonize new sites, penetrate deep periodontal pocket and penetrate into epithelial layers. Cell surface proteins cause dysregulation of host defense, thereby helping to protect the subgingival biofilm and causing host

responsible for alveolar bone resorption [55].

**4.3 Genus** *Campylobacter*

disease [57].

**4.4 Genus** *Treponema*

**250**

tissue destruction [58].

The genus *Fusobacterium* is phylogenetically classified in the family *Fusobacteriaceae*, order *Fusobacteriales*, class *Fusobacteriia* and phylum *Fusobacteria*. Species *Fusobacterium nucleatum* and *Fusobacterium canifelinum* were identified in subgingival plaque from dogs with and without periodontitis [62]. Based on phenotypic and genotypic differences, *F. nucleatum* is divided into five subspecies, namely *F. nucleatum* subspp. *nucleatum*, *F. nucleatum* subspp. *polymorphum*, *F. nucleatum* subspp. *fusiforme*, *F. nucleatum* subspp. *vincentii* and *F. nucleatum* subspp. *animalis*, whose prevalence varies with disease [63]. At present, the mechanisms of pathogenicity of *F. nucleatum* are unclear. Butyrate production is considered a virulence factor. The association of *F. nucleatum* with periodontal disease is probably through its role as a transient colonizer between Gram-positive and Gram-negative species, mainly in humans. Consequently, *F. nucleatum* can serve as a bridge between species that can colonize exposed tooth surfaces (early colonizers), and species that require interactions with other species (late colonizers). Since late colonizers tend to be species associated with periodontal destruction, bridging with *F. nucleatum* could play an important role in determining the pathogenicity of a mature oral biofilm community [64, 65]. Of the large number of periodontal pathogens, *F. nucleatum* is most frequently involved in infections outside the oral cavity, including pneumonia, pyogenic liver abscess, sepsis, infectious endocarditis, brain abscesses and caecal inflammation [66].

## **4.6 Genus** *Parvimonas*

The genus *Parvimonas* is phylogenetically classified in the family *Peptoniphilaceae*, order *Tissierelliales*, class *Tissierellia* and phylum *Firmicutes*. The species *Parvimonas micra* originally classified as *Peptostreptococcus micros* was first reclassified in 1999 to *Mircomonas micros*, and the second time reclassified in 2006 to *Parvimonas micra* [67]. *P. micra* is anaerobic, asaccharolytic Gram-positive coccus found in dogs with periodontitis but not in the healthy dogs [68]. The virulence factors produced by *P. micra*, which may play a role in the pathogenesis of periodontitis, are poorly characterized. *P. micra* may modulate the inflammatory response in the host and contribute to the destruction of periodontal tissue. In addition, *P. micra* is capable of adhering to epithelial cells, also to other periodontal pathogens [69], and is able to form biofilms in conjunction with *Frederiksenia canicola* and *P. gulae*. *P. micra* might provide a catalyst for progressive tissue destruction, inflammation and alveolar bone loss in canine periodontal disease, in keeping with the keystonepathogen hypothesis [68].
