Background
The oral microbiome-dependent nitrate (NO3−)–nitrite (NO2−)–nitric oxide (NO) pathway may help regulate blood pressure. NO2−-producing bacteria in subgingival plaque are reduced in relative abundance in patients with untreated periodontitis compared with periodontally healthy patients. In periodontitis patients, the NO2−-producing bacteria increase several months after periodontal treatment. The early effects of periodontal treatment on NO2−-producing bacteria and the NO3−–NO2−–NO pathway remain unknown. The aim of this study was to determine how periodontal treatment affects the oral NO2−-producing microbiome and salivary NO3− and NO2− levels over time.

Methods
The subgingival microbiota of 38 periodontitis patients was analysed before (baseline [BL]) and 1, 7 and 90 days after periodontal treatment. Changes in NO2−-producing bacteria and periodontitis-associated bacteria were determined by 16s rRNA Illumina sequencing. Saliva samples were collected at all-time points to determine NO3− and NO2− levels using gas-phase chemiluminescence.

Results
A significant increase was observed in the relative abundance of NO2−-producing species between BL and all subsequent timepoints (all p < 0.001). Periodontitis-associated species decreased at all timepoints, relative to BL (all p < 0.02). NO2−-producing species negatively correlated with periodontitis-associated species at all timepoints, with this relationship strongest 90 days post-treatment (ρ = −0.792, p < 0.001). Despite these findings, no significant changes were found in salivary NO3− and NO2− over time (all p > 0.05).

Conclusions
Periodontal treatment induced an immediate increase in the relative abundance of health-associated NO2−-producing bacteria. This increase persisted throughout periodontal healing. Future studies should test the effect of periodontal treatment combined with NO3− intake on periodontal and cardiovascular health.