Extracellular hydrolase activity of the cells of the oral bacterium Streptococcus mutans isolated from man and grown on glucose or xylitol

Growth of xylitol-resistant versus xylitol-sensitive Streptococcus mutans strains in saliva

Five Streptococcus mutans pairs (serotype c S. mutans 10449 and four clinical isolates of S. mutans: 123.1, LG1, OMFA, T10B) were used to find out if the xylitol-resistant (XR) natural mutants of the corresponding xylitol-sensitive (XS) S. mutans parental strains differ in their growth patterns in saliva. The isogenic X natural mutants of the parental S. mutans strains were selected after sequential cultivations in the presence of xylitol and glucose. The XR/XS strains pairs were grown in individual and pooled glucose-supplemented filter-sterilized salivas (one to five sequential cultivations). The two salivas used represented subjects with good or poor support of the growth of S. mutans in vivo. Protease and peptidase activities were determined from the saliva growth media and cell suspensions. Salivary protein profiles were analyzed using SDS-PAGE and native IEF before and after the cultivations. The growth properties of the XR/XS S. mutans pairs were similar in both individual and pooled salivas. Sequential cultivation of all strains did not show any differences in growth patterns. XS strains were inhibited by the presence of xylitol (2% w/v) in pooled saliva, as shown for other glucose-supplemented media. Protease and peptidase activities of the XR/XS S. mutans pairs were low and of similar magnitude. Also, the general hydrolytic properties of most XR/XS S. mutans pairs appeared similar as judged by the small growth-induced changes in salivary protein profiles. In conclusion, saliva, the source of nutrients for salivary microorganisms in vivo, favored neither the XR nor the XS strains of S. mutans.

Effects of xylitol, xylitol-sorbitol, and placebo chewing gums on the plaque of habitual xylitol consumers

Xylitol reduces plaque but the reduction mechanism is largely unknown. The main aim of the present study was to determine whether the xylitol-induced reduction in the amount of plaque and the number of mutans streptococci could be demonstrated in subjects with (presumably) high levels of xylitol-resistant (XR; not inhibited by xylitol) mutans streptococci acquired following previous xylitol consumptions. 37 healthy dental students participated in the double-blind study. All subjects had been uncontrolled, habitual consumers of xylitol-containing products for at least 1 yr before the study. A 1-month washout period was followed by a 2-week test period during which either xylitol, xylitol-sorbitol or unsweetened chewing gum base was chewed 3-5 x a day. Plaque and saliva samples were collected at baseline and at the 2-week point for determination of the amount of plaque, microbiological variables, and hydrolytic enzymes. Mixtures of xylitol and sorbitol seemed to perform equally well with respect to reduction in the amount of plaque but not the number of mutans streptococci. Thus, polyols were the active ingredients of chewing gums able to modulate the amount of plaque and its microbial composition. Xylitol reduced plaque with a mechanism which appeared not to be associated with the study-induced changes in the proportion (%) of mutans streptococci in plaque, the number of salivary mutans streptococci, the proportion of XR strains in plaque or saliva, or the hydrolytic enzyme activities of plaque.

Effects of pulsing with xylitol on mixed continuous cultures of oral streptococci

Continuous culture is a means whereby organisms can be grown at rates approaching those occurring naturally. Moreover, the effect of adding transient excesses of various nutrients to the culture vessel ('pulsing') simulates the effect of dietary challenge on dental plaque organisms. Mixed cultures of Streptococcus mutans T8 and Streptococcus milleri B448 were grown glucose-limited in a chemically defined medium under an atmosphere of 5 per cent carbon dioxide in nitrogen, at a dilution rate of D = 0.1 h-1 and controlled pH of 7.0. The level of arginine in the medium reservoir was adjusted so that Strep. milleri predominated over Strep. mutans in a stable coexistence. After equilibration, the culture vessel was pulsed with various carbohydrates to a final concentration of 5 x 10(-2)mol/L. Samples were then taken at regular intervals and differential viable counts of Strep. mutans and Strep. milleri were done on mitissalivarius agar. Results demonstrated that pulsing with glucose, fructose, 'coupling sugar', lactose, xylose and sorbitol gave Strep. mutans a clear ecological advantage. In direct contrast, pulsing with xylitol resulted in a marked antimicrobial effect on Strep. mutans while Strep. milleri was essentially unaffected. This supports recent findings by other workers that uptake of this pentitol by Strep. mutans in batch culture sets up a 'futile cycle', leading to depressed growth or even cell death.

Carbohydrate-controlled precipitation of apatite with coprecipitation of organic molecules in human saliva: stabilizing role of polyols

Addition of common dietary carbohydrates to Millipore-treated human whole saliva either enhances or inhibits the formation of salivary precipitates, some carbohydrates showing no effect. The purpose of this study was to investigate the precipitation conditions more thoroughly and to elucidate the chemical nature of the precipitates formed. D-Xylose either enhanced precipitation (in long-term incubations) or had no appreciable effect (in 10 minute incubations). Other aldo- and keto-sugars and disaccharides (maltose, sucrose, lactose) generally enhanced precipitation, whereas all polyols (xylitol, D-sorbitol, mannitol, and maltitol) retarded the formation of turbidity in saliva. Xylitol inhibited formation of precipitates also in the presence of D-xylose, dextrans, and starch. Fast protein liquid chromatography (FPLC) of EDTA-soluble pellets obtained by centrifugation of the precipitates produced two major protein fractions (I and II) with a molecular weight of 112,000 and 46,000, respectively. The carbohydrates exerted a selective effect on the relative size of I and II in that polyol incubations resulted in a I to II ratio of 1:3, whereas control incubations (without added sugars) and incubations with other carbohydrates gave ratios of 1:6 to 1:10. Both peaks contained large amounts of acidic amino acids, proline, and glycine. The saliva precipitates contained a substantial portion of a crystalline phase that had the crystal structure of apatite, the individual crystallites being extremely small (less than 1 micron) with a Ca:P ratio of 1.46. The carbohydrates had a similar effect on the overall inorganic composition of the precipitates, but they had a clearly selective effect on the rate of formation of precipitates and on the relative amount of coprecipitating salivary proteins. This selectivity indicates that these carbohydrates, when consumed habitually, may exert different effects on the precipitation of Ca-salts at mineral-deficient enamel and dentine sites.

Proteolytic activities in the supragingival plaque of monkeys (Macaca fascicularis)

Thirteen peptidase substrates were hydrolysed by this plaque. After fasting the monkeys for 24 h, the rates of hydrolysis of N-leucyl-, N-alanyl-, N-isoleucyl- and N-tyrosyl-2-naphthylamines, glycyl-L-proline 4-nitroanilide, N alpha-benzoyl-DL-arginine-2-naphthylamine and L-leucyglycine were significantly increased. Changes in these peptidase activities may serve to enhance the mobilization of amino acids and peptides, and they may explain why the growth rates of dental-plaque bacteria in vivo are generally unaffected by the availability of the host's diet.