The use of Next Generation Sequencing (NGS) techniques has generated a wide variety of blood microbiome data. Due to the large variation in bacterial DNA profiles between studies and the likely high concentrations of cell-free bacterial DNA in the blood, it is still not clear how such microbiome data relates to viable microbiota. For these reasons much remains to be understood about the true nature of any possible healthy blood microbiota and of bacteraemic events associated with disease. The gut, reproductive tracts, skin, and oral cavity are all likely sources of blood-borne bacteria. Oral bacteria, especially those associated with periodontal diseases, are also commonly associated with cardiovascular diseases such as infective endocarditis, and also have been linked to rheumatoid arthritis and Alzheimer’s disease. Periodontal treatment, dental probing, and toothbrushing have been shown to cause transient bacteraemia and oral bacteria from the phyla Firmicutes (e.g. Streptococci) and Bacteroidetes (e.g. Porphyromonas) are found in cardiovascular lesions (CVD). Many studies of blood bacterial DNA content however, find Proteobacteria DNA to be the dominant microbiome component, suggesting a gut origin. Most studies of this type use total DNA extracted from either whole blood or blood fractions, such as buffy coat. Here, using a method that purifies DNA from intact bacterial cells only, we examined blood donated by those with active, severe periodontitis and periodontally healthy controls and show that 43–52% of bacterial species in blood are classified as oral. Firmicutes, consisting largely of members of the Streptococcus mitis group and Staphylococcus epidermidis, were predominant at 63.5% of all bacterial sequences detected in periodontal health and, little changed at 66.7% in periodontitis. Compared to studies using total DNA Proteobacteria were found here at relatively low levels in blood at 13.3% in periodontitis and 17.6% in health. This study reveals significant phylogenetic differences in blood bacterial population profiles when comparing periodontal health to periodontal disease cohorts.

下一代测序（NGS）技术的使用产生了各种各样的血液微生物组数据。由于研究之间的细菌 DNA 谱存在很大差异，并且血液中可能存在高浓度的无细胞细菌 DNA，因此目前尚不清楚此类微生物组数据与活微生物群之间的关系。由于这些原因，对于任何可能的健康血液微生物群以及与疾病相关的菌血症事件的真实性质，仍有许多待了解。肠道、生殖道、皮肤和口腔都可能是血源性细菌的来源。口腔细菌，尤其是与牙周病相关的细菌，通常也与心血管疾病（如感染性心内膜炎）相关，并且还与类风湿性关节炎和阿尔茨海默病有关。牙周治疗、牙科探诊和刷牙已被证明会引起短暂性菌血症，并且在心血管病变 (CVD) 中发现来自厚壁菌门（例如链球菌）和拟杆菌门（例如卟啉单胞菌）的口腔细菌。然而，许多对血液细菌 DNA 含量的研究发现变形菌 DNA 是主要的微生物组成分，这表明其起源于肠道。大多数此类研究使用从全血或血液成分（例如血沉棕黄层）中提取的总 DNA。在这里，我们使用一种仅从完整细菌细胞中纯化 DNA 的方法，检查了患有活动性严重牙周炎的人和牙周健康对照者捐献的血液，结果发现血液中 43-52% 的细菌种类被归类为口腔细菌。厚壁菌门主要由轻症链球菌和表皮葡萄球菌组成，占主导地位，为 63。在牙周健康中检测到的所有细菌序列中有 5% 变化不大，在牙周炎中为 66.7%。与使用总 DNA 的研究相比，我们发现血液中变形菌的水平相对较低，在牙周炎中为 13.3%，在健康人中为 17.6%。这项研究揭示了在比较牙周健康与牙周疾病队列时血液细菌种群概况的显着系统发育差异。