Methods: Six common oral pathogens including Streptococcus mutans NCTC 10449, Lactobacillus acidophilus ATCC 4646, Porphyromonas gingivalis ATCC 33277, Capnocytophaga gingivalis ATCC 33624, Fusobacterium nucleatum ATCC 10953, and Candida albicans ATCC 10231 were cultured in liquid media. Sodium nitrate or sodium nitrite was added to the media to final concentrations of 0, 0.5, 1, 2, or 10 mmol/L. All microorganism were incubated for 24 to 48 hours, the optical densities (OD) of the cell suspensions were determined and the cultures were transferred to solid nutrient broth media to observe the minimum inhibitory concentration and minimum bactericidal/fungicidal concentration for the six tested pathogens.
Results: Nitrite at concentrations of 0.5 to 10 mmol/L had an inhibitory effect on all tested organisms at low pH values. The antimicrobial effect of nitrite increased with the acidity of the medium. Streptococcus mutans NCTC 10449 was highly sensitive to nitrite at low pH values. Lactobacillus acidophilus ATCC 4646 and Candida albicans ATCC 10231 were relatively resistant to acidified nitrite. Nitrate at the given concentrations and under acidic conditions had no inhibitory effect on the growth of any of the tested pathogens.
Conclusion: Nitrite, at a concentration equal to that present in human saliva, is both cytocidal and cytostatic with respect to six principal oral pathogens in vitro, while nitrate at a similar concentration has no antimicrobial effects on these organisms.