Oral-associated bacteria in the gut microbiome of individuals with type 2 diabetes: a secondary analysis of metagenomic data

With an astounding global prevalence, both diabetes mellitus and gum disease pose significant health concerns. Gum disease has been identified as a risk factor for diabetes mellitus, and its treatment has shown improvements in markers of glucose management. We hypothesised that bacteria commonly associated with the oral microbiome could be disproportionately present in the gut of individuals with type 2 diabetes mellitus (T2DM) compared to healthy controls, suggesting a possible association between oral-associated bacteria and metabolic dysregulation. This hypothesis is supported by known interactions between the oral microbiome and systemic health, particularly the role of inflammation in both conditions. Therefore, we aimed to conduct a secondary analysis of whole-genomic sequencing data of studies published over the last twenty years (2004–2024) related to the gut microbiome of patients with T2DM to identify oral-associated bacteria in their gut compared to healthy individuals. We searched for studies related to the gut microbiome, whole metagenomics, and T2DM in Ovid Medline, EMBASE, and Web of Science databases. Studies that included whole metagenomic data from adult populations of all genders with T2DM were selected, resulting in the reanalysis of metagenomic sequencing data from a total of 9 studies (n = 1,224 metagenomes) for bacterial species data. From the 41,689 gut microbial species identified across the selected studies, 497 were classified as of oral-associated bacteria, corresponding with entries in the Human Oral Microbiome Database (HOMD). These oral bacteria comprised 1.19% of the gut microbiome. Notably, twenty oral-associated bacterial species were statistically significant in their presence among patients with diabetes compared to healthy individuals, irrespective of their abundance. Key oral pathogens included Corynebacterium striatum, Staphylococcus capitis, Kingella kingae, Corynebacterium propinquum, Prevotella sp. oral taxon 820, Prevotella scopos, Selenomonas artemidis, Bordetella pertussis, Selenomonas sp. oral taxon 137, and Staphylococcus hominis. Specifically, periodontal pathogens such as, Porphyromonas gingivalis, Tannerella forsythia, and Capnocytophaga sp. oral taxon 332 were found to be significantly higher in patients with T2DM. These bacteria are associated with conditions like endocarditis, bacteremia, and inflammatory responses, which are prevalent in both diabetes and periodontitis. Although causal relationships cannot be directly established, our findings suggest that bacteria typically originating from the oral cavity may be more prevalent in the gut microbiome of patients with T2DM, supporting the potential role of oral-gut microbial interactions in metabolic dysregulation.