An in vitro model system has been used to study the combined influences of fermentable carbohydrate, pH, and fluoride on the stability of complex oral microbial communities. The pH generated from carbohydrate pulses rather than the availability of substrate per se was responsible for the enrichment of the cariogenic species S. mutans and L. casei. The addition of sub-MIC levels of sodium fluoride (1 mmol/L; 19 ppm) reduced both the rate of acid production and the fall in terminal pH from glucose pulses, thereby enabling pH-sensitive bacteria, including many Gram-negative species, to persist. Furthermore, the combination of even a moderately-low environmental pH (ca. pH 5.0) with a low level (1 mmol/L) of fluoride was able to prevent S. mutans from out-competing other species and resulted in its proportions within the bacterial community remaining low. By this mechanism, fluoride could make a significant contribution to preventing dental caries.
Get full access to this article
View all access options for this article.
References
1.
ALEXANDERM. (1971): Microbial Ecology, New York: John Wiley and Sons.
2.
BEIGHTOND., and HAYDAYH. (1980): The Effects of Fluoride on the Growth of Oral Streptococci, Microbios27: 117–124.
3.
BEIGHTOND., and McDOUGALLW.A. (1977): The Effects of Fluoride on the Percentage Bacterial Composition of Dental Plaque, on Caries Incidence and on the in vitro Growth of Streptococcus mutans, Actinomyces viscosus and Actinobacillus sp, J Dent Res56: 1181–1191.
4.
BEIGHTOND; SMITHK.; and HAYDAYH. (1986): The Growth of Bacteria and the Production of Exoglycosidic Enzymes in the Dental Plaque of Macaque Monkeys, Arch Oral Biol31: 829–835.
5.
BOWDENG.H., and HAMILTONI.R. (1987): Environmental pH as a Factor in the Competition between Strains of the Oral Streptococci Streptococcus mutans, S. sanguis, and “S. mitior” Growing in Continuous Culture, Can J Microbiol33: 824–827.
6.
BOWDENG.H.; HARDIEJ.M.; FILLERYE.D.; MARSHP.D.; and SLACKG.L. (1978): Microbial Analyses Related to Caries Susceptibility. In: Proceedings, Methods of Caries Prevention, BibbyB.G., and ShernR.J., Eds; Sp. Supp., Microbiol Abst, London: Information Retrieval, Inc., pp. 83–97.
7.
BOWDENG.H.; ODLUMO.; NOLETTEN.; and HAMILTONI.R. (1982): Microbial Populations Growing in the Presence of Fluoride at Low pH Isolated from Dental Plaque of Children Living in an Area with Fluoridated Water, Infect Immun36: 247–254.
8.
BOYARR.M., and BOWDENG.H. (1985): The Microflora Associated with the Progression of Incipient Lesions in Teeth of Children Living in a Water Fluoridated Area, Caries Res19: 298–306.
9.
BRADSHAWD.J.; McKEEA.S.; and MARSHP.D. (1989): The Use of Defined Inocula Stored in Liquid Nitrogen for Mixed Culture Chemostat Studies, J Microbiol Meth9: 123–128.
10.
BROWNL.R.; WHITEJ.O.; HORTONI.M.; DREIZENS.; and STRECKFUSSJ.L. (1983): Effect of Continuous Fluoride Gel Use on Plaque Fluoride Retention and Microbial Activity, J Dent Res62: 746–751.
11.
DENNISD.A.; GAWRONSKIT.H.; SUDOS.Z.; HARRISR.S.; and FOLKEL.E.A. (1975): Variations in Microbial and Biochemical Components of Four-Day Plaque During a Four-Week Controlled Diet Period, J Dent Res54: 716–722.
12.
DE STOPPELAARJ.D.; VAN HOUTEJ.; and BACKER DIRKSO. (1970): The Effect of Carbohydrate Restriction on the Presence of Streptococcus mutans, Streptococcus sanguis and Iodophilic Polysaccharide-Producing Bacteria in Human Dental Plaque, Caries Res4: 114–123.
13.
HAMILTONI.R., and BOWDENG.H. (1982): Response of Freshly Isolated Strains of Streptococcus mutans and Streptococcus mitior to Change in pH in the Presence and Absence of Fluoride during Growth in Continuous Culture, Infect Immun36: 255–262.
14.
HAMILTONI.R., and BOWDENG.H. (1988): Effect of Fluoride on Oral Microorganisms. In: Fluoride in Dentistry, EkstrandJ., FejerskovO., and SilverstoneL.M., Eds., Copenhagen: Munksgaard, pp. 77–103.
15.
KILIANM.; THYLSTRUPA.; and FEJERSKOVO. (1979): Predominant Plaque Flora of Tanzanian Children Exposed to High and Low Water Fluoride Concentrations, Caries Res13: 330–343.
MARSHP.D. (1989): Host Defenses and Microbial Homeostasis: Role of Microbial Interactions, J Dent Res68: 1567–1575.
18.
McDERMIDA.S.; McKEEA.S.; ELLWOODD.C.; and MARSHP.D. (1986): The Effect of Lowering the pH on the Composition and Metabolism of a Community of Nine Oral Bacteria Grown in a Chemostat, J Gen Microbiol132: 1205–1214.
19.
McDERMIDA.S.; McKEEA.S.; and MARSHP.D. (1987): A Mixed-culture Chemostat System to Predict the Effect of Antimicrobial Agents on the Oral Flora: Preliminary Studies using Chlorhexidine, J Dent Res66: 1315–1320.
20.
McKEEA.S.; McDERMIDA.S.; ELLWOODD.C.; and MARSHP.D. (1985): The Establishment of Reproducible, Complex Communities of Oral Bacteria in the Chemostat using Defined Inocula, J Appl Bact59: 263–275.
21.
MILNESA.R., and BOWDENG.H. (1985): The Microflora Associated with Developing Lesions of Nursing Caries, Caries Res19: 289–297.
22.
MINAHG.E.; SOLOMONE.S.; and ChuK. (1985): The Association between Dietary Sucrose Consumption and Microbial Population Shifts at Six Oral Sites in Man, Arch Oral Biol30: 397–401.
23.
SANDERSW.E., and SANDERSC.C. (1984): Modification of Normal Flora by Antibiotics: Effects on Individuals and the Environment. In: New Dimensions in Antimicrobial Therapy, KootR.K., and SandeM.A., Eds., New York: Churchill Livingstone, pp. 217–241.
24.
SCHAEKENM.J.M.; de JONGM.H.; FRANKENH.C.M.; and van der HOEVENJ.S. (1986): The Effects of Highly Concentrated Stannous Fluoride and Chlorhexidine Regimens on Human Dental Plaque Flora, J Dent Res65: 57–61.
25.
STAATR.H.; GAWRONSKIT.H.; GRESSEYD.E.; HARRISR.S.; and FOLKEL.E.A. (1975): Effects of Dietary Sucrose Levels on the Quantity and Microbial Composition of Human Dental Plaque, J Dent Res54: 872–880.
