Dietary nitrate supplementation influences the oral denitrifying microbiome in human volunteers: a pilot study

Despite recent interest in functional food merits of dietary nitrate, there is a paucity of information on its utility as a pre-biotic for the enrichment of health-promoting oral bacteria. The objective of this investigation was to observe the dynamic change in the denitrifying oral microbiome of healthy human volunteers following supplementation of nitrate enriched diet for a period of two-weeks. The study involved isolation, identification and comparison of nitrate-reducing oral bacteria of five human volunteers before and after supplementation of a nitrate-rich diet. This was further correlated with salivary nitrite contents to understand denitrification efficacy with prolonged dietary nitrate supplementation. A total of 153 bacterial strains were isolated from baseline (BSL) samples of healthy participants, i.e. before supplementation and after dietary nitrate supplementation (ADNS); 32 out of these isolates could be confirmed to be nitrate-reducers. Although members of Firmicutes viz., Streptococcus salivarius, Streptococcus parasanguinis and Actinobacteria viz., Rothia mucilaginosa were present in both BSL and ADNS samples, the relative abundance of Actinobacteria was higher and Firmicutes was lower in ADNS in comparison to BSL samples. Moreover, Proteobacteria were found only in ADNS and not BSL samples. Interestingly, these changes in nitrate-reducing microbiome were correlated with higher salivary nitrite levels on day 14 in comparison to day 1 following acute supplementation of dietary NO₃⁻. Thus, it is being hypothesized that Rothia, Neisseria and Streptococcus spp. which appeared following 14 days of nitrate supplementation, could be more efficient towards reducing nitrate and boosting salivary nitrite levels.