Subgingival microbiome and adjunctive use of probiotics in the treatment of periodontitis in patients with diabetes: a secondary analysis of a randomized clinical trial

Background Adjunctive therapies have been proposed to enhance periodontal outcomes by modulating the subgingival microbiome. However, the microbiological effects of probiotic supplementation in diabetic patients with periodontitis remain unclear, particularly when assessed using high-resolution sequencing methods.Aim To evaluate the effect of a Limosilactobacillus reuteri as an adjunct to subgingival instrumentation on the subgingival microbiome in the treatment of periodontitis in patients with diabetes.Methods This was a secondary analysis of a randomized, triple-blind, placebo-controlled clinical trial. Forty patients with stage II–III periodontitis and diabetes received subgingival instrumentation and either L. reuteri lozenges (n = 19) or placebo (n = 21) for 3 months. Subgingival samples were collected at baseline, 3, and 6 months. The V3–V4 region of the 16S rRNA gene was sequenced and analyzed using QIIME2. Alpha diversity was analyzed with mixed-effects models, beta diversity with PERMANOVA, and differential abundance with linear models.Results A total of 116 high-quality samples were included. Alpha and beta diversity metrics did not show significant differences between groups or across time points. L. reuteri was detected inconsistently in the subgingival microbiome, with low relative abundances and no sustained presence over time. No bacterial species exhibited significant changes in differential abundance between the probiotic and placebo groups over time.Conclusions Adjunctive L. reuteri supplementation did not significantly alter subgingival microbiome diversity or composition over 6 months.