In the initiation or exacerbation of Alzheimer disease, the dissemination of oral microorganisms into the brain tissue or the low-level systemic inflammation have been speculated to play a role. However, the impact of oral microorganisms, such as Porphyromonas gingivalis, on the pathogenesis of Alzheimer disease and the potential causative relationship is still unclear. The present review has critically reviewed the literature by examining the following aspects: (a) the oral microbiome and the immune response in the elderly population, (b) human studies on the association between periodontal and gut microorganisms and Alzheimer disease, (c) animal and in vitro studies on microorganisms and Alzheimer disease, and (d) preventive and therapeutic approaches. Factors contributing to microbial dysbiosis seem to be aging, local inflammation, systemic diseases, wearing of dentures, living in nursing homes and no access to adequate oral hygiene measures. Porphyromonas gingivalis was detectable in post-mortem brain samples. Microbiome analyses of saliva samples or oral biofilms showed a decreased microbial diversity and a different composition in Alzheimer disease compared to cognitively healthy subjects. Many in-vitro and animal studies underline the potential of P gingivalis to induce Alzheimer disease-related alterations. In animal models, recurring applications of P gingivalis or its components increased pro-inflammatory mediators and β-amyloid in the brain and deteriorated the animals' cognitive performance. Since periodontitis is the result of a disturbed microbial homoeostasis, an effect of periodontal therapy on the oral microbiome and host response related to cognitive parameters may be suggested and should be elucidated in further clinical trials.

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牙周微生物与阿尔茨海默病——因果关系？

在阿尔茨海默病的开始或恶化中，口腔微生物传播到脑组织或低水平的全身炎症被推测起作用。然而，口腔微生物的影响，如牙龈卟啉单胞菌，关于阿尔茨海默病的发病机制和潜在的致病关系尚不清楚。本综述通过检查以下方面对文献进行了批判性审查：（a）老年人口中的口腔微生物组和免疫反应，（b）关于牙周和肠道微生物与阿尔茨海默病之间关联的人类研究，（c）动物微生物和阿尔茨海默病的体外研究，以及 (d) 预防和治疗方法。导致微生物菌群失调的因素似乎是衰老、局部炎症、全身性疾病、佩戴假牙、住在疗养院以及无法获得适当的口腔卫生措施。牙龈卟啉单胞菌在死后的脑样本中可检测到。唾液样本或口腔生物膜的微生物组分析显示，与认知健康的受试者相比，阿尔茨海默病的微生物多样性降低，组成不同。许多体外和动物研究强调了牙龈卟啉单胞菌诱导阿尔茨海默病相关改变的潜力。在动物模型中，牙龈卟啉单胞菌或其成分的反复应用增加了大脑中的促炎介质和 β-淀粉样蛋白，并降低了动物的认知能力。由于牙周炎是微生物稳态失调的结果，因此牙周治疗对口腔微生物组和与认知参数相关的宿主反应的影响可能会被提出，并应在进一步的临床试验中加以阐明。