What's Hiding in the Gums of Dogs and Humans?

Using real-time polymerase chain reaction (PCR), researchers in Poland analyzed the subgingival bacterial microflora in dogs and humans with periodontal disease. Study results, which indicated differences in prevalence of specific subgingival bacteria, were recently published in the Journal of Veterinary Science.

Periodontal disease is an infection of the periodontium caused by bacteria. The hundreds of bacterial species living within the healthy oral cavity maintain a homeostatic relationship.

Periodontal disease occurs when plaque accumulates on the teeth, upsetting this homeostasis and triggering an immune response that damages periodontal tissue. This disease typically develops more quickly in dogs than humans, likely because dogs receive oral care less frequently.

Subgingival bacteria, particularly anaerobic gram-negative bacteria, form a protective biofilm during periodontal disease development and colonize into complexes (red, green, orange). Previous studies have reported the importance of the red complex in periodontal disease.

Study Details

Researchers analyzed the subgingival bacterial microflora in 12 adult dogs and 12 adult humans with chronic periodontitis; 6 females and 6 males were in each group. After clearing supragingival plaque, researchers obtained samples from deep gingival pockets (≥4 mm in dogs, ≥5 mm in humans) using sterile paper points. Multiple samples were obtained from each subject and combined into 1 sample, resulting in 24 total samples for the study.

Samples were analyzed using real-time PCR. Although expensive, real-time PCR is sensitive and allows for a relatively quick quantitative analysis of subgingival bacteria. The researchers noted that real-time PCR can improve selection of appropriate periodontal disease treatment and assessment of treatment success.

Following PCR, the relative bacterial percentages and total bacterial counts (CFU/mL) were determined.

Bacterial Percentages

In the canine samples, Porphyromonas gingivalis and Treponema denticola had the highest relative percentages. In the human samples, Capnocytophaga gingivalis and P. gingivalis had the highest relative percentages.

Researchers observed several notable between-group differences in percentages:

• The P. gingivalis percentage was significantly higher in male dogs than in all other groups.
• The T. denticola percentage was significantly higher in female dogs than in all other groups.
• The C. gingivalis percentage was significantly higher in men than in all other groups.

Several bacteria had negligible percentages. For example, Eubacterium nodatum percentages were negligible across all samples. Aggregatibacter actinomycetemcomitans was not detected in dog samples and was detectable only in negligible quantities in the human samples.

Bacterial Counts

The red complex (P. gingivalis, T. denticola, Tannerella forsythia) comprised the largest total bacterial count, with P. gingivalis having the highest count of all identified bacteria. The orange complex (Prevotella intermedia, Peptostreptococcus micros, Fusobacterium nucleatum) comprised the second-largest bacterial count.

Researchers observed several notable between-group differences in bacterial counts:

• T. denticola counts were significantly higher in men than in women.
• P. intermedia counts were significantly higher in women than in female dogs.
• C. gingivalis counts were significantly higher in men than in male dogs and significantly higher in male dogs than female dogs.
• Regardless of sex, P. intermedia and P. micros counts were significantly higher in humans than dogs.

Conclusions

Taken together, these study results indicated similarities in the species of subgingival bacteria present in dogs and humans with periodontal disease; however, the prevalence of specific bacteria varied between species and sexes. Despite the observed prevalence differences, P. gingivalis stood out as the bacterium with the highest count.

Study results contrasted with previous studies’ findings on the subgingival bacterial microflora in dogs and humans. Researchers noted that this could be due to differences in host factors (immunologic status, genetic background) and methods of pathogen detection.

Dr. JoAnna Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.