Salivary microbiome before and 4h after beetroot supplement intake

Tooth decay starts with enamel demineralization due to acidic pH, which generates from sugar fermentation by acidogenic oral bacteria. Previous in vitro work showed that nitrate limits acidification when incubating complex oral communities with sugar for short periods, e.g., 1 to 5 h, resulting from changes in microbiota metabolism or composition. In order to test if a single dose of nitrate can lead to resilience against sugar fermentation in vivo, 12 individuals received a nitrate rich beetroot supplement, which was compared to a placebo in a blinded crossover setting. Sucrose rinses were performed at baseline and 2 h after supplement or placebo intake, and the salivary pH, nitrate, nitrite, ammonium and lactate were measured. After nitrate supplement intake, the pH drop caused by the sucrose rinse was limited by 0.23 points compared to the placebo. Nitrate in saliva correlated negatively with lactate produced and positively with deltapH after sucrose. Two additional pilot studies with each six participants were performed to test the effect of sucrose rinses 1 h and 4 h after nitrate intake. In the 4 h study, nitrate intake was compared to water intake and bacterial profiles were analysed with 16S rRNA gene Illumina sequencing and qPCR detection of Rothia. All sucrose rinses caused a significant pH drop, expect 1 h and 4 h after nitrate supplement intake. After 4 h of nitrate intake, there was less lactate produced compared to ingesting water and one genus, Rothia, increased in abundance. This small but significant increase was confirmed by qPCR. The relative abundance of Rothia and Neisseria correlated negatively with the lactate produced and Neisseria positively with pH after sucrose. Altogether, these results show that nitrate can acutely limit acidification when sugars are fermented, possibly resulting from lactate usage by nitrate reducing bacteria.