Dietary nitrate is reduced to nitrite and nitric oxide by microbial flora, and this activity is beneficial to vascular health. It has been reported that this bacterial process is inhibited by chlorhexidine mouthwash, although the effects of other products are largely unknown. This study examined the effects of several treatments on salivary nitrate/nitrite and nitrate-reducing bacteria. Twelve university staff and students performed mouth-washing with water (control), essential oil, 0.35% povidone-iodine, or 0.0025% chlorhexidine and then ate 100 g lettuce (110 mg nitrate content), followed by collection of saliva and tongue bacteria at the baseline, and 1, 5, and 10 h thereafter. The individual treatments were separated by an interval of one week. Salivary nitrate/nitrite was measured by the calorimetric method, and a representative nitrate-reducing bacterial species, Veillonella dispar, was detected and semi-quantified using a polymerase chain reaction (PCR) assay. Significant increases in salivary nitrate/nitrite were observed for all treatments (all P < 0.05). The PCR assay showed that water, essential oil, and povidone-iodine mouthwash had little effect, whereas V. dispar DNA bands were markedly inhibited after washing with chlorhexidine. These results suggest that essential oil and povidone-iodine mouthwash have little effect on oral nitrate-reducing activity. Salivary nitrite production was not reduced by chlorhexidine, but the fainter band of V. dispar DNA suggests that longer daily use might blunt this nitrate-reducing activity.

Dietary nitrate has several beneficial effects, including blood pressure reduction and improved oxygen consumption efficiency, but in order to do so it must first be reduced to nitrite by oral bacteria. Veillonella spp., a strictly anaerobic group, are the most prevalent nitrate-reducing bacteria in the oral cavity. In response to some early studies that have hinted at inter- and intra-individual variation in salivary nitrate-nitrite conversion capacity, the purpose of the present study was to investigate the incidence of and variation in the Veillonella species V. atypica, V. dispar, and V. rogosae by direct PCR and to assess salivary nitrate-nitrite conversion capacity and its reproducibility after dietary nitrate consumption in 24 elderly individuals. V. atypica, V. dispar, and V. rogosae were detected in 10 (41.7%), 24 (100%), and 14 (58.3%) participants, respectively. The coefficients of correlation between the first and second experiments on increased nitrate/nitrite were 0.637 and 0.583, respectively, both of which were statistically significant (P < 0.01). In both experiments, 6 participants produced relatively low levels of nitrite (<0.5 mM Δ nitrite) while 7 produced relatively high levels (>1.0 mM Δ nitrite). The data suggested that V. dispar was the most prevalent species, being present even in individuals producing low levels of salivary nitrite.