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The relative affinity of various oral streptococci for hydroxyapatite (HA) differed widely. Streptococcus mutans affinity for dextran-coated HA was the highest of all the streptococci to any HA coating. S salivarius had the lowest affinity, and S sanguis affnity was higher then S miteor for saliva-coated HA. Competition for binding sites on saliva-dextran-coated, dextran-coated HA. Hhwever, competition between this pair was not for the same binding site but for closely associated sites.

Contact angle measurements on layers of bacteria were used to determine the bacterial surface free energy (gamma b) of a variety of oral streptococcal strains, both without and after being coated with human whole saliva. At least four isolates of each species, either freshly isolated or laboratory strains, were used. The species Streptococcus mutans, S. sanguis, and S. salivarius were homogeneous, having high surface free energies, and were not affected by saliva treatment (gamma b = 106 +/- 12 and 107 +/- 10 erg X cm-2 in the absence and presence of saliva coating, respectively; n = 20). S. mitis had a very low surface free energy (46 +/- 15; n = 5), which was significantly increased after salivary adsorption (71 +/- 14 erg X cm-2; p less than 0.002). The species S. milleri contained strains with both high and low gamma b. Calculation of the interfacial free energy of adhesion (delta F adh) for bacteria from a saliva suspension to solid surfaces with various arbitrary surface free energies (gamma s) showed that, theoretically, most strains will encounter thermodynamically favorable conditions for adhesion to surfaces with a gamma s above 62 erg X cm-2. However, S. mitis strains not coated with saliva would only be able to adhere to surfaces with gamma s lower than this value. Saliva-coating reverses the calculated relationship with gamma s for these strains. The results indicate that an enamel surface with a low gamma s value would be thermodynamically unfavorable for adhesion of most oral streptococci.

One of the most important questions in ecology is how to explain the co-existence of the variety of physiologically related organisms in the same habitat. A model is presented for the co-existence of Streptococcus species and Actinomyces species in dental plaque. The hypothesis is that these organisms co-exist because they simultaneously utilize several carbon and energy substrates. The hypothesis follows from the observation that the growth yield of oral streptococci and actinomyces in saliva is limited by carbohydrate. Preliminary experiments were undertaken to test the hypothesis using mixed chemostat cultures and gnotobiotic rats. Competition between S. mutans K1R and A. viscosus Ut2 in mixed chemostat cultures on glucose and asparagine was hampered by the early appearance of high-glucose-affinity variants of A. viscosus. From the physiological characteristics of S. sanguis and S. milleri, it might be predicted that simultaneous utilization of carbohydrate and arginine would enable these organisms to co-exist with S. mutans in an ecosystem. To test this mechanism under natural conditions, germ-free rats were inoculated with a combination of S. mutans K1R and S. sanguis P4A7 or the combination S. mutans K1R and S. milleri B448. The rats were fed on three different diets: (1) 58% cornstarch; (2) 48% cornstarch and 10% sucrose; and (3) 53% cornstarch and 5% arginine. The results of this experiment demonstrated that dietary arginine caused a significant decrease of the ratios K1R/P4A7 and K1R/B448 in dental plaque.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimentally induced plaque seemed to originate by direct contact inoculation from the vestibular mucosa and saliva. During the next seven days, this plaque developed its own characteristics. Populations of Streptococcus mutans usually less than 2% of total streptococci population in plaques that were less than three days old, increased between days 3 and 7. Proportions of S sanguis, high in early samples, decreased after day 3. Populations of S salivarius, which usually outnumbered other streptococci, fluctuated widely through day 3, and then increased in proportion in subjects who were more productive of experimental caries, but decreased in subjects who were less productive. Proportions of plaque flora comprising lactobacilli paralleled those of S salivarius.

A prophylaxis followed by three topical applications of an iodine-potassium iodide solution significantly reduced the levels of Streptococcus mutans in fissure and approximal plaques and in saliva. Reductions persisted 20--24 weeks after treatment in salivary and approximal samples. A prophylaxis alone exerted a small and temporary reduction of S. mutans in occlusal fissure plaque, but did not reduce the levels of this organism in approximal plaque or in saliva. A significant relationship existed between the levels of S. mutans in saliva and the proportions of this organism in plaque. The dorsum of the tongue does not appear to constitute a significant reservoir for S. mutans following disinfecting procedures.