Protective effect of salivary nitrate and microbial nitrate reductase activity against caries

Abstract

To test the hypothesis that a combination of high salivary nitrate and high nitrate-reducing capacity are protective against dental caries, 209 children attending the Dental Institute, Barts and The London NHS Trust were examined. Salivary nitrate and nitrite levels, counts of Streptococcus mutans and Lactobacillus spp., and caries experience were recorded. Compared with control subjects, a significant reduction in caries experience was found in patients with high salivary nitrate and high nitrate-reducing ability. Production of nitrite from salivary nitrate by commensal nitrate-reducing bacteria may limit the growth of cariogenic bacteria as a result of the production of antimicrobial oxides of nitrogen, including nitric oxide.

Nitrite reductase is critical for Pseudomonas aeruginosa survival during co-infection with the oral commensal Streptococcus parasanguinis

“…Nitrite is readily available in the human body for conversion to nitrogenous intermediates and has been linked to improved health, particularly in the oral cavity (Hyde et al, 2014). Elevated salivary nitrite concentrations have been associated with a reduction in dental caries, presumably due to the inhibition of the cariogenic pathogen S. mutans by nitric oxide-generating oral commensal bacteria (Doel et al, 2004). It is hypothesized that nitric oxide (or other RNS) generated by denitrifying oral commensals may modulate microbial homeostasis (Hyde et al, 2014), and thereby function as an infection control strategy.…”

Resilience of the Oral Microbiota in Health: Mechanisms That Prevent Dysbiosis

“…In dental plaque, the two primary routes for ammonia generation are the metabolism of arginine via the arginine deiminase system and the hydrolysis of urea by urease enzymes (Liu 2012). Salivary nitrate and the capacity of the microbiota to reduce nitrate to nitrite also appear to have an anti-caries effect, possibly due the production of ammonia and antimicrobial nitric oxide or the consumption of lactate by nitrate reducing species (Doel 2004;Li 2007). Additionally, at pH 5 or lower, acidic decomposition of nitrite to nitric oxide takes place (Schreiber 2010), which could provide negative feedback to acidification (figure 3, blue box "nitrite  nitric oxide").…”

The Role of Nuclear Factor Kappa B in Periodontal Diseases

“…This would be the reason why nitrogen oxides are significantly higher in poor oral hygiene individuals than those with good oral hygiene who have thinner dental biofilm [22]. Many anaerobic facultative bacteria synthesize nitrate reductase in low oxygen tension [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], hence, reduction can take place in the thick biofilm or deep tongue crypts [23]. In thick cariogenic plaque, the low pH level allows the production of acidified nitrite.…”

“…Nitric oxide antibacterial effects are thought to include DNA modifications and interactions with other reactive species; for example, reaction with superoxide produces the highly reactive molecule peroxynitrite [27]. Therefore, nitrate recycling and the availability of large amounts of nitrite in the oral cavity would result in bacteriostatic and possibly bacteriocidal effects which subsequently limit the survival of acidogenic bacteria and decrease caries formation [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26].…”

“…Nitrate from dietary sources is absorbed by the intestine and then re-absorbed from the bloodstream to be secreted into the oral cavity as a component of saliva [8]. Nitratereducing bacteria in the dental biofilm reduce salivary nitrate to nitrite [6][7][8][9][10][11], which is further reduced to nitric oxide (NO) by nitrite reducing bacteria [12,13]. Nitrate secretion in saliva would enhance the survival and growth of bacteria that possess the ability to respire nitrate.…”