Oral microbiota and stroke: towards a specific bacterial signature?

Stroke remains a major public health challenge, where conventional risk factors — such as hypertension or diabetes — are not always sufficient to clarify the complete etiology. What if the key lay partly in the oral cavity? While the link between periodontal pathologies and vascular risk is increasingly well-documented, this meta-analysis explores a specific hypothesis: the existence of a characteristic oral dysbiosis in post-stroke patients.

The objective of this systematic review is to quantify diversity variations (alpha and beta) as well as taxonomic changes within the oral microbiome. To establish this evidence, the authors synthesized data from 11 selected studies, including 746 stroke patients and 552 healthy subjects. The study tests the hypothesis that the pathological state induces a significant alteration of the microbial flora, potentially aggravated by post-stroke functional deficits limiting oral hygiene. This evaluation aims to provide a theoretical basis for the development of targeted oral care strategies for this vulnerable population.

Methodology of the meta-analysis

This systematic review and meta-analysis, registered under the identifier PROSPERO CRD420251235256, was conducted according to PRISMA guidelines. The authors synthesized data from 11 observational studies published up to February 20, 2026, including a total cohort of 1,298 participants: 746 patients who had suffered a stroke and 552 healthy controls.

The selection and analysis criteria were based on the following parameters:

• Population: Adults (≥18 years) with clinically or imaging-confirmed stroke, compared to healthy controls matched for age and sex.
• Sampling: Samples from saliva, gingival crevicular fluid, subgingival plaque or oropharyngeal swabs.
• Microbiological analysis: Diversity data (α and β) and taxonomic composition obtained mainly by 16S rRNA sequencing.
• Statistical tools: Use of RevMan 5.4 software. The effect size was calculated by the standardised mean difference (SMD/Hedges’ g) with a random-effects model.
• Quality assessment: Risk of bias was measured using the Newcastle-Ottawa Scale (NOS). Heterogeneity was quantified by Cochran's Q test and the I² index.

Sensitivity analyses were performed to test the robustness of the results regarding alpha diversity, and publication bias was assessed using funnel plots.

Alterations in microbial diversity and structure

The synthesis of data from the 11 included studies highlights significant changes in the oral microbial landscape in stroke patients. The authors report a trend toward increased bacterial richness and evenness (α-diversity), although these results are tempered by high inter-study heterogeneity.

Analysis of α-diversity

Diversity indices show upward trends, although sensitivity analyses suggest that these results are not entirely robust:

Regarding β-diversity, 8 out of the 9 studies that evaluated this parameter report statistically significant differences in the overall composition of microbial communities between post-stroke patients and healthy controls.

Taxonomic modifications at the Phylum level

Quantitative analysis confirms a specific microbiological signature at the phylum level. The most significant result concerns Bacteroidota, whose abundance is significantly higher in stroke patients (SMD = 0.36; 95% CI: 0.18–0.54; I² = 44%).

The descriptive synthesis of the studies also reveals notable exploratory trends:

• Firmicutes and Spirochaetes: Several studies report an increase in their relative abundance in stroke patients.
• Specific genera: Increases in Streptococcus (notably S. salivarius and S. mutans) have been identified in salivary samples during the initial post-stroke phase.

The authors highlight that the disparities observed between studies (notably for Firmicutes and Bacteroidetes) could be explained by the diversity of sampling sites (saliva, subgingival plaque, or oropharyngeal swabs) and variations in 16S rRNA sequencing protocols.

Clinical decryption: a microbiota in imbalance

The authors of this systematic review report a clear trend: stroke is accompanied by a distinct oral microbial signature. The synthesis shows an increase in α-diversity indices (Observed species, SMD = 0.39; Shannon, SMD = 0.31), suggesting a proliferation of potentially pathogenic species disrupting the usual balance of the oral cavity. The increased prevalence of Bacteroidota (SMD = 0.36, identified in 3 studies) and certain genera such as Streptococcus (notably S. mutans and S. salivarius) in stroke patients reinforces the hypothesis of a link between oral dysbiosis and systemic health.

For the practitioner in the dental office, this link is exacerbated by functional sequelae. Swallowing and chewing disorders, along with the loss of manual dexterity for brushing, create a favorable environment for plaque accumulation. The compiled data indicate that the oral microbiota not only reflects the health status prior to the event but also undergoes characteristic alterations following the stroke, which could influence the overall recovery prognosis.

Limits and nuances

However, these observations must be tempered by the high heterogeneity of the included data (I² > 80% for α-diversity). The synthesis indicates that the diversity results are not robust during sensitivity analyses. Furthermore, although the authors suggest higher abundances of Firmicutes and Spirochaetes, these findings remain exploratory due to an insufficient number of studies for a robust quantitative meta-analysis. These variations highlight the need for more standardized sequencing protocols in future clinical research.

Summary of results

This meta-analysis identifies a specific microbial signature in post-stroke patients, characterized by an increase in α-diversity indices (Observed species and Shannon) and a systematic alteration of β-diversity. The data notably confirm a significantly higher abundance of Bacteroidota (SMD = 0.36) as well as an upward trend in Firmicutes and Spirochaetes compared to healthy subjects.

In concrete terms, for the practitioner:

• Establish an assisted hygiene protocol: Post-stroke functional disorders (mastication, brushing) worsen dysbiosis; specific support is imperative to limit oral infectious foci likely to maintain systemic inflammation.
• Integrating cardiovascular risk in periodontology: The predominance of Bacteroidota and pathogenic genera in these patients underlines the importance of strict periodontal debridement, as oral health is a neurovascular risk marker in this context.

Technical lexicon of the study

16S rRNA sequencing: Bacterial identification method by analyzing hypervariable regions of the 16S ribosomal RNA gene, allowing microbiota profiling without traditional cell culture.

Shannon Index: Alpha diversity indicator that accounts for both the number of species present (richness) and the homogeneity of their distribution (evenness) in the oral sample.

Chao1 Index: Estimator of species richness that emphasizes rare taxa, allowing for the evaluation of the total number of probable species within the oral ecological niche.

Beta diversity: A statistical measure evaluating the similarities or differences in microbial composition between several groups, used here to compare post-stroke patients to healthy controls.

Standardized Mean Difference (SMD): Central statistical tool of this meta-analysis allowing the combination of results from heterogeneous studies by standardizing the observed differences on a common scale.

Bacteroidota: Major bacterial phylum (formerly Bacteroidetes) whose significant increase in the oral cavity is identified by the authors as a potential marker in stroke patients.

Dysbiosis: Qualitative and functional imbalance of the oral microbial ecosystem, cited here as a potential risk factor for systemic pathologies through the maintenance of an inflammatory state.

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