The role of oral microbiome in neurological diseases: mechanisms and clinical significance

The oral microbiome has been increasingly implicated in the development and progression of neurological disorders. This narrative review synthesizes contemporary literature on alterations of oral microbial communities in Alzheimer’s disease, Parkinson’s disease, and migraine and evaluates their potential contribution to neuroinflammation and neurodegeneration. We first outline the core oral taxa that maintain microbial homeostasis and summarize evidence that patients with these neurological conditions exhibit dysbiosis characterized by reduced diversity and enrichment of periodontal pathogens. Proposed mechanisms include hematogenous or neural translocation of oral bacteria and their virulence factors, amplification of systemic inflammation, disruption of the blood-brain barrier, altered production of neuroactive metabolites, and bidirectional signaling along the ‘oral-gut-brain’ axis. On this mechanistic basis, microbiome-targeted strategies, particularly probiotics and fecal microbiota transplantation, have been explored as adjunctive approaches to restore microbial balance and potentially improve neurological outcomes, although available clinical data remain preliminary and heterogeneous. Current evidence is further limited by small samples, methodological variability in microbiome profiling, and a paucity of longitudinal and interventional studies, which hampers causal inference. Future research should adopt standardized sampling and multi-omic approaches and prioritize well-designed clinical trials to determine whether modulation of the oral microbiome can be translated into preventive or therapeutic strategies for neurological diseases.