Association between Eubacterium saphenum and periodontitis: A systematic review.

OBJECTIVE: Although established periodontal pathobionts are frequently detected, their presence alone does not fully explain variations in disease severity, highlighting the need to identify additional microbial contributors. This systematic review evaluates the available evidence on the association between Eubacterium saphenum and the severity of periodontitis. METHODS: The review was conducted in accordance with the PRISMA 2020 framework and registered in PROSPERO (CRD420251273182). Observational studies involving systemically healthy adults were included that compared individuals with periodontitis and periodontal health, reporting detection and/or relative abundance of E. saphenum in saliva and/or subgingival biofilm samples. Study quality was appraised using the AXIS tool, and certainty of evidence was assessed using the GRADE framework. RESULTS: Eight observational studies (304 healthy controls vs. 510 periodontitis cases) from Asia, Europe, and the Americas met the inclusion criteria. Across multiple detection platforms, E. saphenum showed a qualitatively similar direction of association, being more frequently detected and/or present at higher relative abundance in periodontitis than in periodontal health controls. Among studies applying the 2018 periodontal classification system and reporting stage-specific analyses, higher detection or enrichment of E. saphenum was generally observed in advanced disease (stages III-IV). The certainty of evidence was rated as low owing to the observational and predominantly cross-sectional design of the evidence, methodological heterogeneity, and lack of temporality. CONCLUSIONS: Low-certainty evidence suggests a positive directional association between E. saphenum and periodontitis, particularly in advanced Stage III-IV disease. However, longitudinal, interventional, and mechanistic studies are required to clarify temporality and determine whether E. saphenum contributes functionally to periodontal dysbiosis or primarily represents a marker of established disease.