Canine Subgingival Microbiota: With Focus on Treponeme Populations

Objectives: The composition of the subgingival microbiota in dogs is thought to share many similarities with that of humans. Treponeme bacteria are postulated to play a role in canine periodontal disease, analogous to humans.
Objectives: To analyze the bacterial composition of subgingival plaque in dogs, with particular focus on the genus Treponema.
Methods: Multi-site subgingival plaque samples were collected from systemically-healthy dogs (n=7) housed in a commercial facility. DNA was purified (Qiagen, QIAamp DNA Mini kits), and the hypervariable V3-V4 region of the 16S rRNA genes was amplified and sequenced on MiSeq platform PE300 (illumina). Data analyzed by QIIME. PCR primers targeting oral treponeme pyrH genes were used to construct PCR-amplicon ‘TOPO’ clone-libraries, which were ‘Sanger-sequenced’. Datasets were analyzed using various bioinformatic approaches.
Results: A total of 143,670 quality-filtered reads were retrieved for the seven samples (mean 20,524 ± 3,500 reads per sample) and clustered into 744 Operational Taxonomic Units (OTUs) at 97% similarity cut-off. A diverse microbiome was observed that consisted of taxa from 14 different phyla. This was dominated by Bacteroidetes (mean 29.4%), Firmicutes (20.0%) and Proteobacteria (17.6%), with notable levels of TM7 (11.4%), Fusobacteria (8.8%) and Spirochaetes (4.1%) present. 322 pyrH sequences were obtained, which were clustered into 25 distinct ‘genotypes’ (98% identity cut-off). 9 pyrH genotypes (156 sequences) corresponded to phylogroup-1 treponemes; 16 pyrH genotypes (166 sequences) corresponded to phylogroup-2. The majority of phylogroup-1 pyrH genotypes represented novel treponeme phylotypes. The most prevalent phylogroup-2 pyrH genotype was closely related to a ‘Treponema denticola-like’ lineage.
Conclusions: Dog subgingival microbiota has a community composition reasonably similar to that of humans, but contains many distinct phylotypes/taxa that do not inhabit human oral niches. Many of the genetic lineages of oral treponemes found in dogs are highly distinct from those found in humans.