AUTHOR=Rosier Bob T. , Palazón Carlos , García-Esteban Sandra , Artacho Alejandro , Galiana Antonio , Mira Alex 

TITLE=A Single Dose of Nitrate Increases Resilience Against Acidification Derived From Sugar Fermentation by the Oral Microbiome

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=Volume 11 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2021.692883

DOI=10.3389/fcimb.2021.692883

ISSN=2235-2988

ABSTRACT=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., 1-5 h), resulting from changes in microbiota metabolism and/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 (p < 0.05). Nitrate in saliva correlated negatively with lactate produced and positively with ΔpH after sucrose (r= -0.508 and 0.436, respectively, both p < 0.05). Two additional pilot studies were performed to test the effect of sucrose rinses 1 h (n = 6) and 4 h (n = 6) 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 (p < 0.05), 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 (p < 0.05) and one genus, Rothia, increased in abundance. This small but significant increase was confirmed by qPCR (p < 0.05). The relative abundance of Rothia and Neisseria correlated negatively with the lactate produced (r = -0.601 and -0.669, respectively) and Neisseria positively with pH after sucrose (r = 0.669, all p < 0.05). Altogether, these results show that nitrate can acutely limit acidification when sugars are fermented, resulting from lactate consumption by nitrate-reducing bacteria.