Turku sugar studies. IV. An intermediate report on the differentiation of polysaccharide-forming streptococci (S. mutans)

Difference in the xylitol sensitivity of acid production among Streptococcus mutans strains and the biochemical mechanism

Xylitol inhibits the glycolysis and growth of Streptococcus mutans, but to different degrees among strains. Thus, we studied the biochemical mechanism through which the inhibition varies, using S. mutans strains ATCC 31989, NCTN 10449, and NCIB 11723, which are highly sensitive, moderately sensitive, and resistant to xylitol, respectively, under strictly anaerobic conditions such as those found in deep layers of dental plaque. Xylitol (30 mM) decreased the rate of acid production from glucose (10 mM) in ATCC 31989, NCTC 10449, and NCIB 11723 by 86, 26, and 0%, respectively. The activities of the xylitol : phosphoenolpyruvate phosphotransferase system (PEP-PTS) relative to those of glucose : PEP-PTS were 120, 16, and 3%, respectively. In ATCC 31989 and NCTC 10449, intracellular accumulation of xylitol 5-phosphate and decreases of fructose 1,6-bisphosphate and glucose 6-phosphate were observed. Furthermore, in the presence of xylitol (30 mM), glucose : PEP-PTS activities decreased by 34, 17, and 0%, respectively. These findings indicated that the higher the xylitol : PEP-PTS activity was and the more effectively xylitol decreased glucose : PEP-PTS activity, the more sensitive the strain was to xylitol. These results suggest that the following inhibitory mechanisms are active in the xylitol-sensitive mutans streptococci: direct inhibition of glycolytic enzymes by xylitol 5-phosphate derived from xylitol : PEP-PTS and, possibly, indirect inhibition through competition for the phosphoryl donor, HPr-P, between glucose and xylitol : PEP-PTSs.

Xylitol inhibition of anaerobic acid production by Streptococcus mutans at various pH levels

Xylitol inhibits the glycolysis and growth of Streptococcus mutans. We studied the inhibitory effect of xylitol on the acid production of S. mutans at several pH levels under the strictly anaerobic conditions found in the deep layer of dental plaque. Xylitol inhibited the rate of acid production from glucose and changed the profile of acidic end products to formate-acetate dominance, with a decrease in the intracellular level of fructose 1,6-bisphosphate and an intracellular accumulation of xylitol 5-phosphate (X5P). These results were notable at pH 5.5-7.0, but were not evident at pH 5.0. Since the activity of phosphoenolpyruvate phosphotransferase for xylitol was greater at higher pH, it is suggested that xylitol could be incorporated more efficiently at higher pH and that the resultant accumulation of X5P could inhibit the glycolysis of S. mutans more effectively.

Uptake and expulsion of 14C-xylitol by xylitol-cultured Streptococcus mutans ATCC 25175 in vitro

The effect of successive cultivations in the presence of 6% xylitol on the uptake and expulsion of 14C-xylitol was studied using the cells of Streptococcus mutans 25175. Three sequential cultivations did not alter the growth inhibition percentage (approximately 50%) observed in the presence of 6% xylitol. The 14C-xylitol uptake experiments performed with growing and resting cells showed that both the uptake and the expulsion of xylitol were enhanced by xylitol-culturing. Both xylitol-cultured and resting control cells contained only one major labeled compound which was identified as 14C-xylitol 5-phosphate. The label subsequently was expelled from the cells as 14C-xylitol. These results indicate that S. mutans possesses an intracellular xylitol cycle and this cycle is regulated by adding xylitol to the growth medium.

Effect of xylitol-containing carbohydrate mixtures on acid and ammonia production in suspensions of salivary sediment

pH changes and the production of lactic acid, acetic acid and ammonia were studied in suspensions of salivary sediment supplemented with mixtures of xylitol and other carbohydrate sweeteners. The only mixtures which increased the pH values of the suspensions were those containing xylitol alone or mixtures of xylitol and sorbitol. Mixtures of xylitol and Lycasin 80/55 caused a relatively small pH reduction. Xylitol was not able to inhibit the acid production from the easily fermented glucose, fructose and Lycasin 05/60. The levels of lactic acid, determined in the incubation mixtures, directly reflected these pH changes. The levels of acetic acid and ammonia were, however, relatively similar in all incubation mixtures. The results suggest that the inhibitory effects of xylitol on acid production of oral flora should be retained, provided that xylitol is used either alone or in mixtures with slowly fermentable carbohydrates, such as sorbitol and Lycasin 80/55.

Selection for Streptococcus mutans with an altered xylitol transport capacity in chronic xylitol consumers

The effect of long-term consumption of refined xylitol on the natural populations of S. mutans in the human oral cavity has been investigated. Fifty-four S. mutans strains were isolated from adults and children who had been consuming commercial food products containing xylitol for a period of from 1 1/2 to 10 years. Twenty isolates were also obtained from control subjects who had never consumed xylitol-containing commercial food products. The inhibitory effect of xylitol on the isolated strains was determined by monitoring growth on glucose in the presence or absence of xylitol. This was used to define the sensitivity of each isolate to xylitol. Phosphoenolpyruvate:sugar phosphotransferase (PEP-PTS) activities were measured by means of the soluble and membrane fractions prepared from strains from both study populations. It was found that 87% of the fresh isolates from xylitol consumers were xylitol-resistant (XR), compared with only 10% of the strains isolated from the control subjects. The XR strains had low constitutive fructose PTS activity and very low xylitol-phosphorylating capacity. The xylitol-sensitive (XS) strains, however, had much higher levels of constitutive fructose PTS activity and phosphorylated xylitol 16 times more rapidly than did the XR strains. Evidence for the phosphorylation of xylitol by a fructose PEP-PTS in the XS strains was obtained. The growth inhibition by the intracellular accumulation of non-metabolizable toxic xylitol phosphate and its prevention by the presence of fructose are discussed.

The effect of chewing xylitol gum on the plaque and saliva levels of Streptococcus mutans

Eating foods containing sucrose between meals can be highly cariogenic. The use of sucrose substitutes that provide the hedonistic appeal of sucrose, yet are not fermented by the plaque flora to the low pHs that are associated with caries, is a reasonable approach to caries control. Xylitol, a sweet-tasting pentitol, has been reported to cause about an 80% reduction in caries increment when chewed in a gum. The present investigation was designed to determine whether the chewing of xylitol gums affected the salivary and plaque levels of S mutans and lactobacilli. The chewing of xylitol gums for four weeks caused a significant reduction in saliva levels and plaque proportions of S mutans compared with pretreatment values. The levels were also significantly reduced to values obtained by chewing either sorbitol or fructose sweetened gum. The chewing of various gums had no significant effect on the proportions of lactobacilli in the plaque. These findings suggested that the small amounts of xylitol used (about 5 gm) resulted in a suppression of S mutans.

Streptococcus mutans in plaque and saliva after mouthrinsing with SnF2

Mouthrinses with SnF2 in 11 subjects significantly reduced (P less than 0.01) the total colony forming units (CFU) count and the numbers of Streptococcus mutans and Streptococcus sanguis in plaque. The numbers of S. mutans and S. sanguis were significantly more reduced than was the total CFU count. After rinsing with SnF2S. sanguis was present in 97% and S. mutans in only 42% of plaque samples from tooth surfaces where they were detected after rinsing with water. SnF2 also significantly reduced (P less than 0.01) the number of S. mutans in saliva. Mouthrinses with NaF did not markedly affect the number of S. mutans either in plaque or in saliva.

Effects of a carbohydrate-free diet and sugar substitutes on dental plaque accumulation

Plaque accumulation and characteristics were determined gravimetrically, planimetrically, visually, and microbiologically in 24 human subjects who consumed a carbohydrate-free diet for 4 days. In addition, the effects of xylitol-, sorbitol- and sucrose-containing candies upon plaque formed during consumption of the diet were ascertained. Experimental design was such that all 24 subjects traversed each 4-day test period; a 9-day interval between test periods was observed. All plaque measurement methods demonstrated that the subjects in all groups, including a control group which received no candies, accumulated significant amounts of dental plaque. No significant differences in plaque amount could be detected among the xylitol, sorbitol and control groups. However, subjects receiving sucrose-containing candies clearly exhibited larger amounts of plaque. The bacteriological investigations corroborated the clinical observations. The number of microbial colonies from plaque samples taken from the sucrose test group was clearly higher than in the other three groups. In addition, the number of bacteria in plaque samples from the sorbitol group was higher than in the xylitol group. A statistically significant increase in the proportion of anaerobic sorbitol- and xylitol- fermenting bacteria was detected in the sorbitol and xylitol test groups during the 4-day test periods.

Effect of the sweet-tasting protein monellin on growth of a cariogenic bacterium: a microbiological study

Monellin is a protein with an intensely sweet taste and could be considered as a potential alternative sweetener to sucrose. The effect of monellin on the in vitro growth of the cariogenic microorganism Streptococcus mutans was investigated.

Xylitol binding in human dental plaque

Human dental plaque and whole saliva sediment were tested for their ability to bind 14C-labeled sucrose, fructose, glucose, sorbitol, and xylitol. Sucrose, glucose, sorbitol, and fructose were bound to all materials tested, in this decreasing order. The binding was strongest with plaque given a five-second ultrasonic shock, and lowest with salivary sediment. Xylitol was only insignificantly bound, indicating that plaque microorganisms possess specific recognition sites for xylitol to a very restricted extent.

Effect on plaque of a xylitol-containing chewing-gum. A clinical and biochemical study

The effects on plaque induced by single or repeated use of xylitol- and sucrose-containing chewing-gums were studied on twenty subjects refraining from tooth-brushing for three days. Mechanical removal of plaque by chewing during a single period was shown to yield no significant differences between gravimetric values obtained before and after chewing. Daily use of a xylitol-containing chewing-gum reduced by 47% the weight of plaque formed in comparison to a sucrose-containing product, and by 20--41% in comparison to conditions when no chewing-gum was used. The use of a xylitol chewing-gum induced a lower invertase-like activity in plaque extra cellular phase. Results at variance with the gravimetric data were obtained by using a stained plaque scoring system; the eventual inadequacy of such plaque scoring systems was discussed.