Identification of oral bacteria in the gut, atherosclerotic plaque, and cultured blood samples of patients with cardiovascular diseases – A secondary analysis of metagenomic microbiome data

Abstract Background: Cardiovascular diseases (CVDs) encompass various conditions affecting the heart and its blood vessels. Some CVDs, such as ischemic heart disease, angina, stroke, and atherosclerosis, are often linked with oral microbes. The link between the oral cavity and CVDs is complex. Certain pathogenic oral microbes invade the systemic circulation via bacteraemia or other methods and can significantly increase pro-inflammatory cytokine production. Studies have linked oral microbes, systemic inflammation and immune cross-reactivity in the pathogenesis of atherogenesis. Our secondary data analysis aimed to identify oral bacteria from other non-oral sites (i.e. gut, arterial plaque and cultured blood) that could be linked with CVDs. Methods: Taxonomic profiling of the entire data set was performed using Kaiju software; bacteria were identified to the species level and compared with the Human Oral Microbiome Database (HOMD). The oral bacteria in the gut, cultured blood and arterial plaque samples were catalogued, with their average frequency calculated for each sample. Additionally, data were filtered by comparison with the Human Microbiome Project (HMP) database. Results: We identified 17,243 microbial species, of which 410 were present in the HOMD database and further denominated as “oral”. When considering identifications at the species level, all 410 different oral bacterial species were found in at least one gut sample, but only 221 and 169 species were identified in the cultured blood and plaque samples, respectively. Of the 410 species, 153 were present solely in oral-associated environments after comparison with the HMP database, irrespective of their presence in other body sites. The oral bacterial phyla Actinobacteria, Bacteroidetes, Firmicutes, Fusobacterium, Proteobacteria, Spirochetes, Synergistetes and Tenericutes were identified in all three sample types (faeces, arterial plaque and cultured blood) of patients with CVDs. Streptococcus salivarius species was identified as the highest-represented species in the faeces samples. Cutibacterium acnes and Lactobacillus crispatus were found at the highest frequency in cultured blood and plaque samples, respectively. Conclusion: Oral bacteria related to gingival and periodontal disease can be identified in the faeces, arterial plaque and blood samples of patients with CVDs. Identifying these oral bacterial species in nonoral sites of patients with CVDs would explore the link between oral health and general health, including diseases of the cardiovascular system via bacterial translocation.