Antimicrobial effect of acidified nitrite on cariogenic bacteria

The antimicrobial agent nitric oxide (NO) is formed in the mouth and its concentration is directly related to salivary nitrite, which in turn is related to dietary nitrate intake. The aim of this study was to determine whether nitrite under acidic conditions will have an inhibitory effect, possibly ocurring through NO production, on Streptococcus mutans, Lactobacillus casei and Actinomyces naeslundii. Whereas the growth of S. mutans was inhibited by a more acid pH, the addition of nitrite caused a marked, further dose-dependent reduction in bacterial numbers after 24 h of exposure. Similar effects were observed with A. naeslundii and L. casei. The ability of these bacteria to recover from nitrite exposure was also markedly affected by nitrite concentration. At acidity levels below pH 7, low concentrations of nitrite (0.2 mM) caused effective complete killing of S. mutans, with similar effects on the other organisms tested. These results demonstrate the possibility that nitrite in saliva has an effect on the growth and survival of cariogenic bacteria.