Review of the dynamic role of the oral microbiome in health and disease

The oral microbiome, the community of microorganisms (bacteria, fungi, viruses and archaea) residing in the mouth, plays a vital role in health. Distinct microbial profiles exist due to the unique biological properties of the various habitats which are constantly bathed in saliva. Under healthy conditions, the oral microbiome has a favourable commensal association with its environment. However, the build-up of dental plaque can trigger host-mediated inflammation leading to conditions such as gingivitis and periodontitis. Oral infection has been linked to systemic diseases and microbes are postulated to contribute via spread of infection due to transient bacteraemia, circulation of microbial toxins or systemic inflammation from an immune response.

Advances in sequencing and bioinformatics capabilities have led to numerous studies describing bacterial and fungal associations with periodontal health or disease. Crucially, several publications have indicated a lack of similarity (< 20%) between the microbial communities in dogs and cats with those in the human oral cavity. This knowledge creates new opportunities for tailored species-specific diagnostic and health monitoring solutions for cats and dogs. The main technological approaches deployed include sequencing of the entire bacterial community, quantification of individual species and measurement of bacterial biproducts. High throughput sequencing provides a comprehensive profile of the entire microbial community, but is resource-intensive, requires bioinformatics expertise and has a lengthy turnaround time. Quantification of individual species (e.g. qPCR) is cheap, fast and routinely used for diagnostics but can result in false negatives as some pets may not have the bacterial biomarker being screened for. Detection of bacterial biproducts involves measuring bacterial activity (e.g., volatile sulphur compound production or protease activity) and is rapid, cheap and applicable to point-of-care use. However, byproduct levels can fluctuate due to host and environmental factors and can lack specificity so may need to be combined with other measures.

Diet composition may impact the oral microbiome by providing a food source that enriches for certain bacterial species. For example, westernised human diets have led to an increase in acid-producing bacteria within the oral cavity which is likely the reason for the high prevalence of dental caries observed. In dogs and cats, the influence of diet is less well understood, however, molecular screening tools have shown that dry diets shift the bacterial population towards those associated with healthy gingiva and vice versa for wet diets. Dental chews have also been demonstrated to modulate the oral microbiome, increasing the relative abundance of taxa associated with oral health and decreasing the abundance of those associated with periodontal disease.

The oral microbiome plays a critical role in maintaining overall health. Advances in molecular methods and bioinformatics have significantly enhanced our understanding of the distinct microbial communities in the oral cavities of dogs and cats, enabling more precise and rapid diagnostic and monitoring tools. Oral care interventions have been shown to modulate the oral microbiome towards a healthier profile. Continued research integrating microbial profiling with clinical outcomes is required to optimise strategies for improving oral and systemic health in pets.