Colonization of rat molar teeth by mutans streptococci with different salivary agglutination characteristics

The oral implantation of salivary agglutination-positive and -negative mutans streptococci was studied using streptomycin resistant (StrR) organisms. StrR Streptococcus mutans strains Ingbritt and NCTC 10449 are agglutinated by rat saliva and the StrR strains Streptococcus sobrinus 6715-13 and Strep. mutans GS5 are not. Four groups of Sprague-Dawley rats were inoculated orally with each organism (one per group) and fed a sucrose diet. A further two groups of animals were similarly inoculated with either the agglutination-positive Strep. mutans Ingbritt or the agglutination-negative Strep. sobrinus 6715-13 and fed a glucose diet. StrR streptococci were recovered from smooth-surface dental plaque of all animals on the sucrose diet with no significant difference in the recovery of agglutination-positive Strep. mutans strains Ingbritt and NCTC 10449 and agglutination-negative Strep. mutans GS5. However, the recovery of agglutination-negative Strep. sobrinus 6715-13 from smooth-surface plaque of animals on either the sucrose or the glucose diets was significantly lower than that of the other strains. Agglutination-positive Strep. mutans Ingbritt colonized smooth enamel surfaces of animals on the sucrose and the glucose diets in numbers that were not significantly different. However, the colonization of such surfaces by agglutination-negative Strep. sobrinus 6715-13 was significantly enhanced by the sucrose diet. Agglutination-positive and -negative StrR mutans streptococci were recovered from fissure plaque of all inoculated sucrose-fed animals in numbers that were not significantly different. Successful colonization of smooth enamel surfaces by the StrR streptococci resulted in increased smooth-surface caries.(ABSTRACT TRUNCATED AT 250 WORDS)     

Caries inhibitory activity of cacao bean husk extract in in-vitro and animal experiments

Cacao bean husk extract (CBH) was examined for inhibitory effects on the caries-inducing properties of mutans streptococci in vitro and on caries development in specific pathogen-free Sprague-Dawley rats infected with mutans streptococci. CBH reduced the growth rate of almost all oral streptococci examined, which resulted in the reduction of acid production. Furthermore, insoluble glucan synthesis by the glucosyltransferases from Streptococcus mutans MT8148R and Streptococcus sobrinus 6715 was significantly inhibited by CBH. Hence, the sucrose-dependent cell adherence of mutans streptococci was also depressed by CBH. The administration of CBH in drinking water resulted in significant reductions of caries development and dental plaque accumulation in rats infected with either Strep. sobrinus 6715 or Strep. mutans MT8148R, and the minimum cariostatic concentration was 1.0 mg/ml. These results indicate that CBH possesses powerful anticariogenic potential.     

Latex agglutination test for detection of mutans streptococci in relation to dental caries in children.

A simple and rapid system based on a latex agglutination (LA) reaction was devised for the detection of mutans streptococci in dental plaque. Latex particles were sensitized with antibodies against whole cells of Streptococcus mutans strains MT8148 (serotype c), MT703R (e) and OMZ175 (f) and Strep. sobrinus strains B13 (d) and 6715 (g). These sensitized particles were agglutinated within a few minutes after addition of 1.0-10 ng serotype-specific antigen from the homologous organisms or the nitrous acid extract of whole cells at 10(5)-10(6) c.f.u. The LA test specifically differentiated not only mutans streptococci from the other oral streptococci but also Strep. sobrinus from Strep. mutans. The LA test was also applicable to extracts of plaque from 206 human subjects who harboured mutans streptococci. In clinical trials, the outcome of the LA test correlated significantly with the number of mutans streptococci found in plaque (p less than 0.0001), which was quantified by the selective cultivation of mutans streptococci. Furthermore, the LA test discriminated between Strep. mutans and Strep. sobrinus from human dental plaque. The sensitivity and the specificity of the LA test for detection of mutans streptococci were 78.9 and 100%. The degree of reactivity in the LA test correlated significantly with the number of decayed tooth surfaces (p less than 0.0001) and decayed and filled tooth surfaces (p less than 0.0001). These results suggest that the LA test could be useful clinically for the detection of mutans streptococci in dental plaque as well as serving as a caries-activity test.     

Suppression of Streptococcus sobrinus 6715 (g) in plaques by Streptococcus mutans 32K (c)

The dental plaque of 96 healthy donors was screened for the production of such antibacterial substances as mutalipocin and bacteriocin and 192 strains of mutans streptococci isolated: 28 produced mutalipocin and 22 produced bacteriocin. Mutalipocin produced by these 28 S. mutans strains possessed similar biochemical and biological characteristics of well-characterized mutalipocin-producing strain S. mutans 32K (serotype c). When equal amounts of S. mutans 32K and S. sobrinus 6715 (g) were cultured together, cells of S. sobrinus 6715 were completely killed in 18 h. In addition, S. mutans 32K inhibited in vitro plaque formation by S. sobrinus 6715, and S. mutans 32K also eliminated in vitro plaque preformed by S. sobrinus 6715. In rat experiments, S. mutans 32K could preemptively colonize in plaque preformed by S. sobrinus 6715. On the other hand, S. sobrinus 6715 could not colonize in plaque preformed by S. mutans 32K. The results indicate that S. mutans serotype c which produces antibacterial substances is able to invade denatl plaque and replace the other mutans streptococci. This investigation offers one of the possible explanation why S. mutans serotype c is a predominant species among mutans streptococci in human plaque.     

Suppression of Streptococcus sobrinus 6715 (g) in plaques by Streptococcus mutans 32K (c)

The dental plaque of 96 healthy donors was screened for the production of such antibacterial substances as mutalipocin and bacteriocin and 192 strains of mutans streptococci isolated: 28 produced mutalipocin and 22 produced bacteriocin. Mutalipocin produced by these 28 S. mutans strains possessed similar biochemical and biological characteristics of well-characterized mutalipocin-producing strain S. mutans 32K (serotype c). When equal amounts of S. mutans 32K and S. sobrinus 6715 (g) were cultured together, cells of S. sobrinus 6715 were completely killed in 18 h. In addition, S. mutans 32K inhibited in vitro plaque formation by S. sobrinus 6715, and S. mutans 32K also eliminated in vitro plaque preformed by S. sobrinus 6715. In rat experiments, S. mutans 32K could pre-emptively colonize in plaque preformed by S. sobrinus 6715. On the other hand, S. sobrinus 6715 could not colonize in plaque preformed by S. mutans 32K. The results indicate that S. mutans serotype c which produces antibacterial substances is able to invade dental plaque and replace the other mutans streptococci. This investigation offers one of the possible explanation why S. mutans serotype c is a predominant species among mutans streptococci in human plaque.     

In-vitro adherence of oral streptococci in the presence of sucrose and its relationship to cariogenicity in the rat

Streptococcus sanguis I gave a significantly greater percentage coverage (cell-pellicle attachment) of saliva-coated glass in the presence of sucrose than did Strep. sanguis II (p less than 0.025), and both these gave greater percentage coverages than the other species tested, between which no significant differences were noted. There was a large number of significant differences in clump size (cell-cell attachment) between species-pairs. Among the mutans streptococci, there were significant differences in the percentage coverage between Streptococcus rattus/Streptococcus mutans (p less than 0.05) and Strep. rattus/Streptococcus sobrinus (p less than 0.01), and in clump size between all species-pairs with the exception of Streptococcus cricetus or Strep. sobrinus and Strep. mutans. The rank order of species in relation to fissure caries was mutans streptococci greater than Streptococcus salivarius greater than Streptococcus milleri greater than Strep. sanguis greater than Streptococcus faecalis greater than Streptococcus mitis greater than Streptococcus lactis. There was a significant correlation between percentage coverage in vitro and fissure caries in vivo for strains of Strep. sanguis (p less than 0.05) and pooled strains of Strep. mitis and Strep. sanguis (p less than 0.01). On comparing data for adherence in the presence or the absence of sucrose, the sugar had no effect on the percentage coverage of the seven species tested, but significantly increased the clump size of the mutans streptococci (p less than 0.01) and Strep. sanguis (p less than 0.05).     

Effects of chlorhexidine gluconate in drinking water on dental caries and oral microorganisms in the Syrian hamster

Hamsters infected with Streptococcus sobrinus (formerly Streptococcus mutans) strain 6715-1119 were given high-sucrose diet 2000. After 5 days, they were presented with 0.05 or 0.1 per cent w/v chlorhexidine gluconate (CHX) continuously in their drinking water, which was well-tolerated. Compared to infected but untreated controls, their caries scores were less by 84 and 97 per cent respectively after 42 days. Coronal dental plaque deposits were reduced in a dose-related fashion. Culture plates of oral swabs showed reductions in Strep. sobrinus and total streptococci after 10 and 35 days of CHX. Hamster oral streptococci were more sensitive to CHX than were lactobacilli but neither was completely eliminated. The incidence of stained tooth deposits after 0.1 per cent CHX was slightly but not significantly greater than in controls.     

Trehalulose does not induce dental caries in rats infected with mutans streptococci

The effects of trehalulose, a structural isomer of sucrose, and a syrup (TP syrup) rich in trehalulose and palatinose on caries development were examined in specific pathogen-free Sprague-Dawley rats. Streptococcus mutans MT8148R and Streptococcus sobrinus 6715 fermented the syrup which resulted in acid production, while both strains were found not to utilize trehalulose. Furthermore, trehalulose did not serve as a substrate for glucosyltransferases of these mutans streptococci to synthesize water-insoluble glucan, and it inhibited the sucrose-dependent adherence of mutans streptococci to a glass surface. Although trehalulose induced no significant dental caries in specific pathogen-free rats infected with either MT8148R or 6715, TP syrup was found to induce significant but low dental caries. Furthermore, replacement of the dietary sucrose content with trehalulose resulted in a significant reduction of caries development in rats infected with strain 6715.     

In vitro antimicrobial activity of propolis and Arnica montana against oral pathogens

Arnica and propolis have been used for thousands of years in folk medicine for several purposes. They possess several biological activities such as anti-inflammatory, antifungal, antiviral and tissue regenerative, among others. Although the antibacterial activity of propolis has already been demonstrated, very few studies have been done on bacteria of clinical relevance in dentistry. Also, the antimicrobial activity of Arnica has not been extensively investigated. Therefore the aim here was to evaluate in vitro the antimicrobial activity, inhibition of adherence of mutans streptococci and inhibition of formation of water-insoluble glucan by Arnica and propolis extracts. Arnica montana (10%, w/v) and propolis (10%, w/v) extracts from Minas Gerais State were compared with controls. Fifteen microorganisms were used as follows: Candida albicans--NTCC 3736, F72; Staphylococcus aureus--ATCC 25923; Enterococcus faecalis--ATCC 29212; Streptococcus sobrinus 6715; Strep. sanguis--ATCC 10556; Strep. cricetus--HS-6; Strep. mutans--Ingbritt 1600; Strep. mutans--OMZ 175; Actinomyces naeslundii--ATCC 12104, W 1053; Act. viscosus OMZ 105; Porphyromonas gingivalis; Porph. endodontalis and Prevotella denticola (the last three were clinical isolates). Antimicrobial activity was determined by the agar diffusion method and the zones of growth inhibition were measured. To assess cell adherence to a glass surface, the organisms were grown for 18 h at 37 degrees C in test-tubes at a 30 degree angle. To assay water-insoluble glucan formation, a mixture of crude glucosyltransferase and 0.125 M sucrose was incubated for 18 h at 37 degrees C in test-tubes at a 30 degree angle. Arnica and propolis extracts (20 microl) were added to these tubes to evaluate the % of inhibition of cell adherence and water-insoluble glucan formation. The propolis extract significantly inhibited all the microorganisms tested (p < 0.05), showing the largest inhibitory zone for Actinomyces spp. The Arnica extract did not demonstrate significant antimicrobial activity. Cell adherence and water-insoluble glucan formation were almost completely inhibited by the propolis extract at a final concentration of 400 microg/ml and 500 microg/ml, respectively. The Arnica extract showed slight inhibition of the adherence of the growing cells (19% for Strep. mutans and 15% for Strep. sobrinus) and of water-insoluble glucan formation (29%) at these same concentrations. Thus, the propolis extract showed in vitro antibacterial activity, inhibition of cell adherence and inhibition of water-insoluble glucan formation, while the Arnica extract was only slightly active in those three conditions.     

An improved method for measuring aggregation of certain streptococcal bacteria found in dental plaque

Various cells were incubated with either dextran or sucrose and the reaction was terminated by the addition of a 20 per cent solution of formaldehyde. A reaction mixture consisting of cells and aggregated cells was applied to a step-gradient glycerol column (0-60 per cent) and 0.5 ml fractions were collected from the bottom of the column. Non-aggregated cells remained in the top layer of the column. Aggregated cells settled in the 30 per cent glycerol layer as determined by either spectrophotometric or radioactive methods. The amount of aggregated cells demonstrated in this layer increased with either incubation time or concentration of sucrose, dextran or cells. Cells of Strep, mutans strains 6715, AHT, 10449, OMZ-176, OMZ-175 and two mutants of Strep. mutans strain 6715 (designated C4 and C307) aggregated strongly. Cells of Strep. mutans strain LM7 aggregated weakly, whereas cells of Strep. mutans 6715 mutant UAB165, a mutant defective in aggregation. Strep. mutans strain BHT, Strep. salivarius and Strep. sanguis did not aggregate in the presence of either sucrose or dextran. Experiments testing co-aggregation between two different types of cells were done by using 3H-labelled and 14C-labelled cells. Strep. mutans strain 6715 co-aggregated with Strep. sanguis in the presence of sucrose or dextran, whereas Strep. mutans strain 6715 did not aggregate with Strep. salivarius. The method separates aggregated from non-aggregated cells and enables quantitation of sucrose- or dextran-induced aggregation and co-aggregation.     

The influence of a novel propolis on mutans streptococci biofilms and caries development in rats

A flavonoids-free Brazilian propolis (type 6) showed biological effects against mutans streptococci and inhibited the activity of glucosyltransferases. This study evaluated the influence of the ethanolic extract of a novel type of propolis (EEP) and its purified hexane fraction (EEH) on mutans streptococci biofilms and the development of dental caries in rats. The chemical composition of the propolis extracts were examined by gas chromatography/mass spectrometry. The effects of EEP and EEH on Streptococcus mutans UA159 and Streptococcus sobrinus 6715 biofilms were analysed by time-kill and glycolytic pH drop assays. Their influence on proton-translocating F-ATPase activity was also tested. In the animal study, the rats were infected with S. sobrinus 6715 and fed with cariogenic diet 2000. The rats were treated topically twice a day with each of the extracts (or control) for 5 weeks. After the experimental period, the microbial composition of their dental plaque and their caries scores were determined. The results showed that fatty acids (oleic, palmitic, linoleic and stearic) were the main compounds identified in EEP and EEH. These extracts did not show major effects on the viability of mutans streptococci biofilms. However, EEP and EEH significantly reduced acid production by the biofilms and also inhibited the activity of F-ATPase (60-65%). Furthermore, both extracts significantly reduced the incidence of smooth surface caries in vivo without displaying a reduction of the percentage of S. sobriuns in the animals' plaque (P < 0.05). However, only EEH was able to reduce the incidence and severity of sulcal surface caries (P < 0.05). The data suggest that the cariostatic properties of propolis type 6 are related to its effect on acid production and acid tolerance of cariogenic streptococci; the biological activities may be attributed to its high content of fatty acids.     

Noncariogenicity of maltitol in specific pathogen-free rats infected with mutans streptococci.

The effect of maltitol on caries development was examined in an experimental caries system employing specific pathogen-free (SPF) Sprague-Dawley rats. Fourteen strains of oral streptococci, including mutans streptococci, did not utilize the maltitol nor produce sufficient acid to demineralize tooth enamel. Furthermore, maltitol did not serve as a substrate for glucosyltransferases of either Streptococcus mutans MT8148R or Streptococcus sobrinus 6715 to synthesize water-insoluble glucan. Maltitol induced no significant dental caries in SPF rats infected with these mutans streptococci, and replacement of the dietary sucrose content with maltitol resulted in a trend towards caries reduction in SPF rats.     

Interaction of structural isomers of sucrose in the reaction between sucrose and glucosyltransferases from mutans streptococci

Structural isomers of sucrose, i.e. disaccharides composed of glucose and fructose molecules with different glucosidic linkages, were examined for their effect on the reaction between sucrose and various glucosyltransferases (GTases) from Streptococcus mutans MT8148 and Streptococcus sobrinus 6715. Trehalulose (alpha 1-1), turanose (alpha 1-3), maltulose (alpha 1-4), and palatinose (alpha 1-6) were used as the sucrose analogues. Mutans streptococci were found not to utilize these sucrose analogues. Analysis of enzymatic products of GTase and sucrose with thin layer chromatography clearly revealed that glucan synthesis from [14C]sucrose by the various purified GTase preparations from S. mutans and S. sobrinus was inhibited in the presence of these sucrose analogues except turanose, resulting in the release of increased amounts of [14C]fructose and [14C]oligosaccharides. It was also found that the fructose residues in the oligosaccharides were derived from those of sucrose analogues but not sucrose itself. The Lineweaver-Burk plots of the substrate saturation kinetics of GTase vs sucrose indicated increased Km and Vmax in the presence of sucrose analogue, as compared with sucrose alone. Finally, these sucrose analogues except turanose inhibited sucrose dependent cellular adherence of S. sobrinus 6715 to a glass surface, while they scarcely inhibited the adherence of S. mutans MT8148. Among the analogues, maltulose appeared the most effective inhibitor against GTases in general.     

Effects of NaF and SnF2 on growth, acid and glucan production of several oral streptococci

The effects of low concentrations of these fluorides on Streptococcus sobrinus, Streptococcus mutans, Streptococcus salivarius, Streptococcus mitior and Streptococcus sanguis were investigated. Without fluoride, mutans streptococci (Strep. mutans and Strep. sobrinus) produced more acid than the other strains; both fluorides reduced acid production in all strains. NaF had little effect on growth; SnF2 decreased growth in all strains, most evidently in the Strep. mutans. In all growth conditions, Strep. sobrinus produced the most alkali-soluble glucan. Both fluorides enhanced alkali-soluble glucan production in mutans streptococci while only SnF2 enhanced this in the other streptococci.     

Noncariogenicity of erythritol as a substrate.

Erythritol is a sugar alcohol produced by Aureobasidium sp. from glucose. It is 75-80% as sweet as sucrose and is also nonhygroscopic. The aim of this study was to evaluate this sugar substitute from a cariological point of view. Erythritol was neither utilized as a substrate for the lactic acid production nor for plaque formation of mutans streptococci (serotypes a-h) and certain oral microorganisms. It was not utilized for water-insoluble glucan synthesis or cellular adherence by glucosyltransferase from Streptococcus mutans PS-14 (c) and Streptococcus sobrinus 6715 (g). Finally, a significantly lower caries score (3.1 +/- 0.5; mean +/- SEM) was observed in specific pathogen-free rats infected with S. sobrinus 6715 and fed with a diet containing 26% erythritol, as compared to control rats fed with a diet containing 26% sucrose (60.5 +/- 2.0). Also, rats provided a diet containing 56% erythritol chocolate (23.8% erythritol) and challenged with S. mutans PS-14 exhibited a significantly lower caries score (6.7 +/- 0.8) compared to the sucrose chocolate group (82.8 +/- 2.8). The main conclusion from this study is therefore that erythritol is a promising sugar substitute from a cariological point of view.     

Non-cariogenicity of erythritol as a substrate

Erythritol is a sugar alcohol which is obtained through a cultivation of glucose and Aureobasidium sp. The sugar is about 70-80% as sweet as sucrose and is also non-hygroscopic. The effect of erythritol on cariogenicities of mutans streptococci (serotype a-h) and certain oral microorganisms was studies. Erythritol was not utilized as a substrate for the growth, lactic acid production and plaque formation of mutans streptococci (serotype a-h). It did not serve as a substrate for cellular aggregation of mutants streptococci (serotype d, g, h) and was not utilized water-insoluble glucan synthesis and cellular adherence by glucosyltransferase from S. mutans PS-14 (c) or S. sorbrinus 6715 (g). Erythritol was not also utilized for the growth and lactic acid production of certain oral microorganisms although some growth was seen with Actinomyces viscosus. SPF SD rats infected with S. sobrinus 6715 were fed a diet containing 26% erythritol or 26% sucrose for 53 days. A significantly (p less than 0.01) lower caries score (mean +/- SE; 3.1 +/- 0.5) was observed in the rat fed a diet containing erythritol than the control (60.5 +/- 2.0). The caries inhibition rate is 94.9%. Also, rats infected with S. mutans PS-14 were fed a diet containing 56% erythritol chocolate or 56% sucrose chocolate for 58 days. The mean total caries score of rats fed a diet containing 56% erythritol chocolate was 6.7 +/- 0.8, while the mean total caries score of rats fed a diet containing 56% sucrose chocolate was 82.8 +/- 2.8. The value between both groups was significant at 0.01 level, and the caries inhibition rate is 91.9%.     

Detection of mutans streptococci by latex agglutination test and its application as a caries-activity test

The number of mutans streptococci in saliva and dental plaque has been reported to correlate with the incidence of dental caries. This report describes a simple and rapid diagnostic method for the detection of mutans streptococci in dental plaque using latex agglutination (LA) test. Latex particles (0.876 microns, diameter) were sensitized with partially purified antibodies against whole cells of Streptococcus mutans MT8148 (c), MT703R (e) and OMZ175 (f) and Streptococcus sobrinus B13 (d) and 6715 (g). Whole cells of mutans streptococci or dental plaque was extracted with a mixture of 8M sodium nitrite (5 microliters) and 2M acetic acid (5 microliters) for five minutes and neutralized with 2M sodium hydroxide (10 microliters), and the extract and the sensitized latex suspension (20 microliters) were mixed and the grade of agglutination reaction was read macroscopically after ten minutes standing at room temperature. The LA tests could detect 1.0 10ng of purified serotype antigen and 10(5)-10(6) CFU of live cells of mutans streptococci and specifically distinguish not only the mutans streptococci from the other streptococci but also S. mutans from S. sobrinus. However, cross-reactions were still observed among the serotypes c, e and f of S. mutans or between the serotypes d and g of S. sobrinus. Plaque samples were collected from 168 children (2 to 12 years of age) and the 0.1 mg (wet weight) were applied to the LA tests. At the same time, the total number of mutans streptococci in plaque and the serotypes of each isolate were determined. The results of LA reaction correlated significantly with the number of mutans streptococci in plaque (chi-square analysis; p less than 0.0001). The LA tests discriminated between S. mutans and S. sobrinus in dental plaque. It was found that the latex particles sensitized with anti-serotype c and/or e S. mutans antibodies were most effective in demonstrating mutans streptococci, and they were used in the following studies. The results of LA reaction correlated significantly with both the number of decayed tooth surfaces and the number of decayed and filled tooth surfaces. These results suggest that the LA test in mutans streptococci can be useful for the detection of mutans streptococci in dental plaque and also as a caries-activity test at dental clinics.     

Effects of oral streptococci on biofilm formation by cariogenic bacteria in dual species cultures

The effects of oral commensal streptococci (Streptococcus sanguinis, Streptococcus gordonii, Streptococcus mitis, and Streptococcus salivarius) on biofilm formation by cariogenic mutans streptococci (Streptococcus mutans and Streptococcus sobrinus) were investigated. Cell suspensions were cultured on 96-well microtiter plates coated with or without salivary components (SC), and in flow cell systems coated with SC in tryptic soy broth including 0.25% sucrose without dextrose (TSB). The resultant biofilm formations were stained using safranin or a LIVE/DEAD BacLight Viability Kit, and examined with absorbance at 492 nm or using confocal laser scanning microscopy. Mutans streptococci and S. sanguinis biofilms were formed significantly on the polystyrene surfaces in TSB. Further, in combination cultures, S. sanguinis formed a sufficient biofilm when cultured with S. mutans. However, when S. sanguinis was cultured with S. sobrinus, biofilm formation was slightly inhibited. S. gordonii also inhibited biofilm formation in the culture with S. sobrinus, but not when cultured with S. mutans. S. mitis and S. salivarius collapsed the biofilm morphology and inhibited volume development in some conditions when cultured with S. mutans or S. sobrinus. Biofilm formation by mutans streptococci was challenged and collapsed on the whole by culturing with each of the other oral streptococci. These results indicate that co-culturing of multiple species of mutans streptococci and other oral streptococci has physical effects related to previous attachment and colonization on the surface, as well as biological effects to regulate biofilm formation.     

Dental caries in congenitally athymic rats

The importance of the immune response in dental infection was evaluated in heterozygous (rnu/+) normal and homozygous (rnu/rnu) congenitally athymic "nude" Rowett rats. Animals of both types were infected, or immunized and infected, with mutans streptococci (Streptococcus sobrinus strain 6715). The mean numbers of S. sobrinus cells recovered from the nude rats were higher than those from comparable (immune/nonimmune) normal rats in 10 of 12 possible comparisons. Also, S. sobrinus constituted a greater percentage of the total streptococci in the nude rats compared with normal animals (6 of 6 possible comparisons). Antibody to S. sobrinus whole cells or to S. sobrinus glucosyltransferase from nude rats in serum or in saliva was significantly lower (or absent) than that of comparable normal rats. This was seen after infection, but was most pronounced after immunization (and infection). Dental caries was also significantly elevated in the congenitally athymic animals. Immunologic deficiency of congenitally athymic rats can lead to a greater infection level with mutans streptococci and increased dental caries.     

Mutans streptococci, lactobacilli and caries experience in 12-year-old Icelandic urban children, 1984 and 1991

Abstract In order to evaluate changes in salivary counts of cariogenic bacteria and relate these to trends in caries experience, stimulated saliva was collected from a 20% random sample of 12-yr-old residents of Reykjavik. Iceland (252 children) in 1991 under conditions consistent with those of a survey conducted in 1984. The mean and median counts of salivary mutans streptococci and lactobacilli remained similar in the two studies. However, the frequency distribution at lower levels of mutans streptococci differed significantly between 1991 and 1984, e.g. in the present study 25.8% of the children had < 10⁵ compared with 13.8% in the study 1984. The mean caries prevalence in the permanent dentition (DFS_tot) was 11.0, which is significantly lower than in 1984 (mean DFS_tot 28.8). A significant difference in caries prevalence was found at various levels of salivary mutans streptococci. Strep. mutans (serotype c/e/f) was carried by all mutans streptococci-positive children, save one child, who carried only Strep. sobrinus. The proportion of 12-yr-olds who carried Strep, sobrinus had decreased significantly to 15.7% from 34.0% in 1984. Significantly more children with Strep. sobrinus showed high levels of total mutans streptococci than children with only Strep. mutans. As the case was in 1984 significantly more Strep. sobrinus carriers had a high level of salivary lactobacilli as well as higher caries prevalence than the children who did not carry this species.