Effect of sodium nitrite and ascorbic acid on the growth and acid production of Streptococcus mutans

Nitrite at acid pH has been shown to be antibacterial particularly against the highly cariogenic species Streptococcus mutans. Nitrite might yield nitrosamines in vivo but ascorbic acid (vitamin C) could counteract these potential ill effects. The aim of this study is to determine whether ascorbic acid would interfere with the ability of sodium nitrite to suppress growth and acid production of S. mutans, NCTC 10449T and NCTC 10832. Strains were grown in Fastidious Anaerobe Broth before exposure to 200 mM nitrite in the presence of various concentrations of ascorbic acid (0.0, 5.7, 11.4, 17.0, 22.7, 28.4, 56.8, 85.2 mM). End pH was measured after 24 h exposure and cultures were serially diluted for viable counts. Statistical significance of differences in end pH values, each from 10 experiments, was determined using the Mann–Whitney U-Test. At all concentrations of ascorbic acid plus 200 mM nitrite plus S. mutans the pH was higher than with controls lacking ascorbic acid and/or nitrite (p≥0.001). S. mutans was viable (between 4.5×108 and 7.9×109 cfu ml−1) after growth in the presence of ascorbic acid at all concentrations without nitrite, whereas it was not detected when 200 mM nitrite was also present. Conclusions: ascorbic acid does not prevent the action of nitrite against S. mutans. Therefore ascorbic acid could be used in conjunction with nitrite to help counteract potential ill effects for humans.