Antimicrobial effect of acidified nitrate and nitrite on six common oral pathogens in vitro.
BACKGROUND
Salivary nitrate is positively correlated with plasma nitrate and its level is 9 times the plasma level after nitrate loading. Nitrate in saliva is known to be reduced to nitrite by oral bacteria. Nitrate and nitrite levels in saliva are 3 - 5 times those in serum in physiological conditions respectively in our previous study. The biological functions of high salivary nitrate and nitrite are still not well understood. The aim of this in vitro study was to investigate the antimicrobial effects of nitrate and nitrite on main oral pathogens under acidic conditions.


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 medium. Sodium nitrate or sodium nitrite was added to the medium to final concentrations of 0, 0.5, 1, 2, and 10 mmol/L. All of the microorganisms were incubated for 24 to 48 hours. The optical densities (OD) of cell suspensions were determined and the cultures were transferred to solid nutrient broth medium 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.


CONCLUSIONS
Nitrite, at a concentration equal to that in human saliva, is both cytocidal and cytostatic to six principal oral pathogens in vitro, whereas nitrate at a similar concentration has no antimicrobial effect on these organisms.
Xia
Deng-sheng
DS
Salivary Gland Disease Center and Molecular Laboratory for Gene Therapy, Capital Medical University School of Stomatology, Beijing 100050, China.
Liu
Yin
Y
Zhang
Chun-mei
CM
Yang
Sheng-hui
SH
Wang
Song-lin
SL
D000890:Anti-Infective Agents / Q000494:pharmacology*; D002176:Candida albicans / Q000187:drug effects; D016967:Fusobacterium nucleatum / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007779:Lactobacillus acidophilus / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D009055:Mouth / Q000382:microbiology*; D009566:Nitrates / Q000032:analysis / Q000097:blood / Q000494:pharmacology*; D009573:Nitrites / Q000032:analysis / Q000097:blood / Q000494:pharmacology*; D016966:Porphyromonas gingivalis / Q000187:drug effects; D012463:Saliva / Q000737:chemistry; D013295:Streptococcus mutans / Q000187:drug effects
D000890:Anti-Infective Agents; D009566:Nitrates; D009573:Nitrites