Diversity in Antagonistic Interactions between Commensal Oral Streptococci and Streptococcus mutans

Arginine metabolism via the arginine deiminase system (ADS) of oral bacteria generates ammonia, which can increase the pH of oral biofilms and decrease the risk for dental caries. Antagonistic interactions between ADS-positive and cariogenic bacteria in oral biofilms may be an important ecological determinant of caries. This study investigated the antagonistic potential and mechanisms of clinical isolates of arginolytic streptococci on and by Streptococcus mutans UA159, a well-characterized cariogenic human isolate. Low-passage isolates of Streptococcus gordonii, Streptococcus sanguinis, Streptococcus parasanguinis, Streptococcus australis, and Streptococcus cristatus inhibited the growth of S. mutans to various degrees when they were inoculated on growth media first or simultaneously with S. mutans. The antagonistic effects of arginolytic strains against S. mutans and the production of H2O2 by these strains were enhanced during growth in a less-rich medium or when galactose was substituted for glucose as the primary carbohydrate source. Pyruvate oxidase was the dominant pathway for H2O2 production by arginolytic strains, but lactate oxidase activity was also detected in some strains of S. gordonii and S. cristatus. UA159 inhibited the growth of all tested arginolytic strains when inoculated first, especially in aerobic conditions. However, the antagonistic effects of S. mutans on certain strains of S. gordonii and S. australis were not observed during anaerobic growth in the presence of arginine. Thus, arginolytic commensal streptococci may have a synergistically positive impact on the ecology of oral biofilms by moderating biofilm pH while antagonizing the growth and virulence of caries pathogens.

Effect of Vital Tooth Bleaching on Surface Roughness and Streptococcal Biofilm Formation on Direct Tooth-Colored Restorative Materials

OBJECTIVE

To compare the effect of simulated bleaching with a 10% carbamide peroxide (CP) or a 40% hydrogen peroxide (HP) system on surface roughness of resin composite and resin-modified glass ionomer cement (RMGI) and streptococcal biofilm formation on these surfaces.

METHODS AND MATERIALS

Specimens of nanofilled resin composite and RMGI (n=108 each) were randomly divided into three groups (n=36 each): no treatment control, 10% CP, and 40% HP. The surface roughness values (Ra) were measured before and after treatments. The specimens in each group were randomly divided into three subgroups (n=12) and incubated with Streptococcus mutans, Streptococcus sanguinis, and trypticase soy broth control for 24 hours. Biofilm formation was quantified by crystal violet staining, and the structure was visualized by scanning electron microscopy. The differences between the mean changes in Ra between the 10% CP and 40% HP groups of each material were evaluated with an independent t-test. The quantity of biofilm formation on each material was analyzed with one-way analysis of variance with the post hoc Tukey test ( α=0.05).

RESULTS

Surface roughness significantly increased after bleaching in all groups. There was no significant difference between the 10% CP and 40% HP groups of each material. For S. mutans biofilm formation, bleaching with 10% CP and 40% HP increased biofilm on both materials compared to controls. However, S. sanguinis biofilm formation was significantly higher on bleached resin composite but not on RMGI specimens.

CONCLUSIONS

Simulated bleaching with 10% CP or 40% HP increased both surface roughness and biofilm formation on resin composite and RMGI, except for S. sanguinis biofilm on RMGI.

The road less traveled - defining molecular commensalism with Streptococcus sanguinis

The commensal oral microbial flora has evolved with the human host to support colonization of the various intraoral sites without triggering a significant immune response. In exchange, the commensal microbes provide critical protection against invading pathogens. The intrinsic ability of the oral flora to create a symbiotic microbial community with the host can be disturbed, selecting for the overgrowth of a dysbiotic community that can result in dental diseases, such as caries and periodontitis. Although the mechanisms of molecular pathogenesis in oral diseases are well characterized, much less is known about the molecular mechanisms used by the commensal flora to maintain oral health. Here we focus on the commensal species Streptococcus sanguinis, which is found in abundance in the early oral biofilm and is strongly correlated with oral health. Streptococcus sanguinis exhibits a variety of features that make it ideally suited as a model organism to explore the molecular basis for commensalism. As such, this review will describe our current mechanistic understanding of S. sanguinis commensalism and speculate upon its molecular traits that may be exploitable to maintain or restore oral health under conditions that would otherwise lead to disease.

Effects of Repeated Screw Tightening on Implant Abutment Interfaces in Terms of Bacterial and Yeast Leakage in Vitro: One-Time Abutment Versus the Multiscrewing Technique

Screw loosening can damage the interfaces of implant components, resulting in susceptibility to contamination of the internal parts by microorganisms. The aim of this study was to investigate the impact of abutment screw retightening on the leakage of two different types of bacteria, Streptococcus sanguinis and Fusobacterium nucleatum, and of the yeast Candida albicans. Two types of implant-abutment systems with tube-in-tube interfaces were tested. Groups A and B each used a different type of system that consisted of 20 different pieces that were assembled according to the manufacturer's torque recommendations; four samples in each group were closed just one time, four samples three times, four samples five times, four samples seven times, and four samples nine times. The implants of groups A and B were contaminated with 0.1 μL of microbial solution just before being assembled for the last time to minimize the possibility of contamination. Results showed a direct correlation between the number of colony-forming units grown in the plates and the closing/opening cycles of the implant-abutment systems. Within the limitations of this study, the results indicate the possibility that repeated closing/opening cycles of the implant-abutment unit may influence bacterial/yeast leakage, most likely as a consequence of decreased precision of the coupling between the abutment and the internal part of the dental implant. These findings suggest that a one-time abutment technique may avoid microbiologic leakage in cases of implant-abutment systems with tube-in-tube interfaces.

Interference of Antimicrobial Activity of Combinations of Oral Antiseptics Against Streptococcus mutans, Streptococcus sanguinis, and Lactobacillus acidophilus

PURPOSE

The purpose of this study was to compare the effects of combinations of sodium fluoride and antiseptic compounds on the growth of Streptococcus mutans, Streptococcus sanguinis, and Lactobacillus acidophilus.

METHODS

The agar diffusion assay was used to determine bacterial growth inhibition.

RESULTS

Of the combinations tested, 0.1 percent sodium fluoride and five percent povidone iodine produced synergistic antibacterial effects against S. mutans and S. sanguinis. The combination of 10 percent povidone iodine and 0.5 percent sodium hypochlorite produced additive antibacterial effects against L. acidophilus. Interference was seen in some combinations such as 0.01 percent chlorhexidine and 0.25 percent sodium lauryl sulphate, 0.5 percent sodium hypochlorite and 10 percent povidone iodine, and 0.01 percent cetyl pyridium chloride and 0.1 percent sodium fluoride. However, 0.1 percent sodium fluoride combined with 0.01 percent chlorhexidine did not interfere with the antibacterial effects of chlorhexidine against S. mutans or S. sanguinis.

CONCLUSIONS

Combinations of common antiseptics and fluoride compounds can produce interference, synergistic, or additive effects. The combination of 0.1 percent sodium fluoride and five percent povidone iodine had the greatest potential for suppression of S. mutans.

Characterization of the arginolytic microflora provides insights into pH homeostasis in human oral biofilms

A selected group of oral bacteria commonly associated with dental health is capable of producing alkali via the arginine deiminase system (ADS), which has a profound impact on the pH of human oral biofilms. An increased risk for dental caries has been associated with reduced ADS activity of the bacteria in oral biofilms. Arginolytic bacterial strains from dental plaque samples of caries-free and caries-active adults were isolated and characterized to investigate the basis for differences in plaque ADS activity between individuals. Fifty-six ADS-positive bacterial strains were identified by 16S rRNA gene sequencing, and their ADS activity levels were compared under standard growth conditions. The spectrum of bacterial ADS activity ranged from 45.2 to 688.0 units (mg protein)(-1). Although Streptococcus sanguinis was the most prevalent species, other Streptococcus sp. were also represented. Biochemical assays carried out using 27 ADS-positive strains under conditions known to induce or repress ADS gene expression showed substantial variation in arginolytic activity in response to pH, oxygen and the availability of carbohydrate or arginine. This study reveals that the basis for the wide spectrum of arginolytic expression observed among clinical strains is, at least in part, attributable to differences in the regulation of the ADS within and between species. The results provide insights into the microbiological basis for intersubject differences in ADS activity in oral biofilms and enhance our understanding of dental caries as an ecologically driven disease in which arginine metabolism moderates plaque pH and promotes dental health.

Propolis varnish: antimicrobial properties against cariogenic bacteria, cytotoxicity, and sustained-release profile

Varnishes are preparations that differ in the polymeric matrix and therapeutical agents. In dentistry they are used to prevent caries. In this study we developed a propolis varnish, considering propolis properties against cariogenic bacteria. To a chitosan polymeric base (CHV) was added ethanolic propolis extract in different concentrations: PV1 (5%), PV2 (10%), and PV3 (15%). Antimicrobial activity was carried out against Streptococcus mutans (SM), Streptococcus sanguinis (SG), Streptococcus salivarius (SS), and Lactobacillus casei (LC) through agar diffusion method. The three propolis concentrations incorporated were effective in inhibiting the growth of all microorganisms, but without significant difference between the zones of inhibition observed. Cytotoxicity assay was done by MTT method. Data were analyzed by one-way ANOVA and Bonferroni test. None of the varnishes were cytotoxic, keeping 80% of viable cells, while CHV allowed cellular proliferation (120%). Sustained-release test was carried out by applying 40 μ L of each varnish in the buccal surface of bovine teeth and kept in an ethanol/water solution removed in regular times. According to the "independent model approach," the release profiles were distinct from each varnish and the most prolonged was PV3 (8 weeks). Varnish formulations had satisfactory antimicrobial activity against cariogenic bacteria and have a low cytotoxicity (<50%).

SpxA1 involved in hydrogen peroxide production, stress tolerance and endocarditis virulence in Streptococcus sanguinis

Streptococcus sanguinis is one of the most common agents of infective endocarditis. Spx proteins are a group of global regulators that negatively or positively control global transcription initiation. In this study, we characterized the spxA1 gene in S. sanguinis SK36. The spxA1 null mutant displayed opaque colony morphology, reduced hydrogen peroxide (H₂O₂) production, and reduced antagonistic activity against Streptococcus mutans UA159 relative to the wild type strain. The ΔspxA1 mutant also demonstrated decreased tolerance to high temperature, acidic and oxidative stresses. Further analysis revealed that ΔspxA1 also exhibited a ∼5-fold reduction in competitiveness in an animal model of endocarditis. Microarray studies indicated that expression of several oxidative stress genes was downregulated in the ΔspxA1 mutant. The expression of spxB and nox was significantly decreased in the ΔspxA1 mutant compared with the wild type. These results indicate that spxA1 plays a major role in H₂O₂ production, stress tolerance and endocarditis virulence in S. sanguinis SK36. The second spx gene, spxA2, was also found in S. sanguinis SK36. The spxA2 null mutant was found to be defective for growth under normal conditions and showed sensitivity to high temperature, acidic and oxidative stresses.

An electron microscopy study of the diversity of Streptococcus sanguinis cells induced by lysozyme in vitro

Bacterial virulence could be altered by the antimicrobial agents of the host. Our aim was to identify the damage and survival of Streptococcus sanguinis induced by lysozymes in vitro and to analyse the potential of oral microorganisms to shirk host defences, which cause infective endocarditis. S. sanguinis ATCC 10556 received lysozyme at concentrations of 12.5, 25, 50 and 100 microg/ml. Cells were examined by electron microscopy. The survival was assessed by colony counting and construction of a growth curve. Challenged by lysozymes, cells mainly exhibited cell wall damage, which seemed to increase with increasing lysozyme concentration and longer incubation period in the presence of ions. Cells with little as well as apparent lesion were observed under the same treatment set, and anomalous stick and huge rotund bodies were occasionally observed. After the removal of the lysozyme, some damaged cells could be reverted to its original form with brain heart infusion (BHI), and their growth curve was similar to the control cells. After further incubation in BHI containing lysozyme, S. sanguinis cell damage stopped progressing, and their growth curve was also similar to the control cells. The results suggested that the S. sanguinis lesions caused by the lysozyme in the oral cavity may be nonhomogeneous and that some damaged cells could self-repair and survive. It also indicated that S. sanguinis with damaged cell walls may survive and be transmitted in the bloodstream.

Effect of lactoperoxidase on the antimicrobial effectiveness of the thiocyanate hydrogen peroxide combination in a quantitative suspension test

BACKGROUND

The positive antimicrobial effects of increasing concentrations of thiocyanate (SCN-) and H2O2 on the human peroxidase defence system are well known. However, little is known about the quantitative efficacy of the human peroxidase thiocyanate H2O2 system regarding Streptococcus mutans and sanguinis, as well as Candida albicans. The aim of this study was to evaluate the effect of the enzyme lactoperoxidase on the bactericidal and fungicidal effectiveness of a thiocyanate-H2O2 combination above the physiological saliva level. To evaluate the optimal effectiveness curve, the exposure times were restricted to 1, 3, 5, and 15 min.

RESULTS

The bactericidal and fungicidal effects of lactoperoxidase on Streptococcus mutans and sanguinis and Candida albicans were evaluated by using two test mixtures of a 2.0% (w/v; 0.34 M) thiocyanate and 0.4% (w/v; 0.12 M) hydrogen peroxide solution, one without and one with lactoperoxidase. Following the quantitative suspension tests (EN 1040 and EN 1275), the growth of surviving bacteria and fungi in a nutrient broth was measured. The reduction factor in the suspension test without lactoperoxidase enzyme was < 1 for all three tested organisms. Thus, the mixtures of 2.0% (w/v; 0.34 M) thiocyanate and 0.4% (w/v; 0.12 M) hydrogen peroxide had no in vitro antimicrobial effect on Streptococcus mutans and sanguinis or Candida albicans. However, the suspension test with lactoperoxidase showed a high bactericidal and fungicidal effectiveness in vitro.

CONCLUSION

The tested thiocyanate and H2O2 mixtures showed no relevant antimicrobial effect. However, by adding lactoperoxidase enzyme, the mixtures became not only an effective bactericidal (Streptococcus mutans and sanguinis) but also a fungicidal (Candida albicans) agent.

Effect of xylitol/chlorhexidine versus xylitol or chlorhexidine as single rinses on initial biofilm formation of cariogenic streptococci

OBJECTIVES

Oral bacteria implying a natural resistance may deteriorate the antibacterial efficacy of chlorhexidine on cariogenic microorganisms. Xylitol, mostly applied via chewing gum, is known to possess favorable plaque-reducing properties. The aim of this study was to investigate the effect of a xylitol rinse formulated as pure solution or combined with chlorhexidine on the viability of Streptococcus sanguis (early colonizer of human teeth) and Streptococcus mutans (the most causal strain for caries) during initial steps of biofilm formation.

METHOD AND MATERIALS

After exposure to the test solutions, the bacteria suspended in human sterile saliva were allowed to attach to human enamel slides for 60 minutes in a preclinical flow chamber system. The bacterial vitality of suspended and attached cells was monitored using 2 fluorescent DNA stains by epifluorescence microscopy. Further parameters measured were the total bacterial cell counts on enamel slides and growth of suspended streptococci.

RESULTS

The sensitivity of S mutans to pure chlorhexidine or in combination with xylitol is contrary to the natural resistance of S sanguis to chlorhexidine. The combination of xylitol/chlorhexidine showed a statistically significant antivital effect on S sanguis cells compared to the pure agents xylitol and chlorhexidine. The bacterial cell density on enamel and bacterial reproduction on agar plates were similarly affected by the combination of xylitol/chlorhexidine or the single substances.

CONCLUSION

The newly discovered synergistic antivital effect of xylitol combined with chlorhexidine may contribute to the favorable potential of xylitol use for the improvement of new formulations of caries-preventive mouthrinses.

The effect of saliva or serum on bacterial and Candida albicans colonization on type I collagen

Colonization of Candida albicans on oral surfaces can serve as a reservoir for disseminated infections, such as aspiration pneumonia and gastrointestinal infection, particularly in the immunocompromised host. Therefore, the aim of this study was to investigate the effects of salivary and serum pellicles on C. albicans, Streptococcus mutans, S. sanguis, Lactobacillus and Actinomyces colonization on type I collagen, a major organic component of periodontal ligaments. The colonization potential of two isolates each of C. albicans, S. mutans and S. sanguis, and a single isolate each of Lactobacillus and Actinomyces to uncoated (control), saliva-coated or serum-coated type I collagen plates (surface area 143 mm(2), Cell Disk; Sumitomo, Tokyo, Japan) was examined using a bioluminescent adenosine triphosphate assay based on firefly luciferase-luciferin system. The results revealed that with mutans streptococci, a saliva pellicle was significantly more effective in promoting bacterial colonization compared with the pellicle-free collagen disc, and the serum-coated sample significantly inhibited the colonization of streptococci (anova; P < 0b01). In contrast, in the case of C. albicans, Lactobacillus and Actinomyces isolates, a serum pellicle was significantly more effective in promoting the colonization, followed by saliva pellicle and uncoated specimen (anova; P < 0b01). These results suggested that crevicular fluid rich in seruminous components would promote the colonization of Candida, Lactobacillus and Actinomyces on type I collagen as opposed to streptococci which showed greater avidity to saliva-coated collagen.

Resistance to acidic and alkaline environments in the endodontic pathogen Enterococcus faecalis

BACKGROUND/AIMS

This study aimed to investigate the biochemical mechanisms employed by the endodontic pathogen Enterococcus faecalis to confer acid- and alkali-resistance and to compare these with the mechanisms of representative oral streptococci.

METHODS

E. faecalis JCM8728, Streptococcus mutans NCTC10449 and Streptococcus sanguinis ATCC10556 were used to assess both acid- and alkali-resistance by examining: (i) growth in complex media; (ii) stability of intracellular pH (pH(in)); (iii) cell durability to leakage of preloaded BCECF (2',7'-bis-(2-carboxyethyl)-5,6-carboxy-fluorescein); and (iv) cell permeability to SYTOX-Green.

RESULTS

Growth was initiated by E. faecalis at pH 4.0-11.0, by S. mutans at pH 4.0-9.0 and by S. sanguinis at pH 5.0-9.0. The pH(in) was similar to the extracellular pH in S. mutans and S. sanguinis at pH 5-10, while the pH(in) of E. faecalis was maintained at approximately 7.5-8.5 when extracellular pH was 7.5-10 and was maintained at levels equivalent to the extracellular pH when pH < 7.5. Cell membranes of E. faecalis were resistant to BCECF leakage when extracellular pH was 2.5-12 and to SYTOX-Green permeability at pH 4-10. The cell membrane durability to extracellular pH in E. faecalis was higher than that observed in the Streptococcus strains.

CONCLUSION

Compared to S. mutans, E. faecalis was found to be equally resistant to acid and more resistant to alkalis. The results suggest that pH-resistance in E. faecalis is attributed to membrane durability against acid and alkali, in addition to cell membrane-bound proton-transport systems. These characteristics may account for why E. faecalis is frequently isolated from acidic caries lesions and from persistently infected root canals where calcium hydroxide medication is ineffective.

Role of Streptococcus sanguinis sortase A in bacterial colonization

Streptococcus sanguinis, a normal inhabitant of the human oral cavity, has low cariogenicity, though colonization on tooth surfaces by this bacterium initiates aggregation by other oral bacteria and maturation of dental plaque. Additionally, S. sanguinis is frequently isolated from infective endocarditis patients. We investigated the functions of sortase A (SrtA), which cleaves LPXTG-containing proteins and anchors them to the bacterial cell wall, as a possible virulence factor of S. sanguinis. We identified the srtA gene of S. sanguinis by searching a homologous gene of Streptococcus mutans in genome databases. Next, we constructed an srtA-deficient mutant strain of S. sanguinis by insertional inactivation and compared it to the wild type strain. In the case of the mutant strain, some surface proteins could not anchor to the cell wall and were partially released into the culture supernatant. Furthermore, adherence to saliva-coated hydroxyapatite beads and polystyrene plates, as well as adherence to and invasion of human epithelial cells were reduced significantly in the srtA-deficient strain when compared to the wild type. In addition, antiopsonization levels and bacterial survival of the srtA-deficient mutant were decreased in human whole blood. This is the first known study to report that SrtA contributes to antiopsonization in streptococci. Our results suggest that SrtA anchors surface adhesins as well as some proteins that function as antiopsonic molecules as a means of evading the human immune system. Furthermore, they demonstrate that SrtA of S. sanguinis plays important roles in bacterial colonization.

Interaction between GIC and S. sanguis biofilms: Antibacterial properties and changes of surface hardness

OBJECTIVE

The aim of this study was to investigate the interaction of Streptococcus sanguis with two glass-ionomer formulations (GIC:A containing fluoride and GIC:B without fluoride) with particular reference to bacterial growth and changes in hardness of the cement with respect to time.

MATERIALS AND METHODS

Discs of two water activated glass-ionomer cements were prepared according to the manufacturer's instruction. Hydroxyapatite discs (HA) were used as controls. 3D laser scanning technique was used to characterize surface roughness and area of the substrate prior to growing biofilms. Surface hardness was evaluated before and after biofilm growth. A constant depth film fermenter system (CDFF) was used to grow S. sanguis biofilms on the specimens in a similar manner to that described previously by Wilson et al. in 1995. For susceptibility measurement, specimens were removed from CDFF aseptically over periods up to 14d after the first colonization with bacteria. Counts of viable bacterial in the accumulating biofilm layer on each surface were measured and converted to colony forming units per unit surface area. To determine the effect of storage media, hardness discs were exposed to distilled water, lactic acid pH 4, lactic acid pH 5, citric acid pH 5, artificial saliva and S. sanguis biofilms. Twenty-four hours after preparing and subsequent autoclaving, specimens were transferred to a vessel containing 40 ml storage medium. The specimens were investigated for periods up to 7d.

RESULTS

The viable counts of S. sanguis per mm2 on GIC:A were significantly less than those on HA and GIC:B during the first 5d (p<0.05). The viable counts of bacteria on the surface of GIC:B were lower during the initial 5d when compared to HA. Exposure of GIC:A and GIC:B to different medium produced softening to the surface of cement. It is apparent that the effects of the biofilms are significantly greater than storage in water but similar to storage in lactic acid pH 5.

CONCLUSIONS

This investigation showed that the growth of S. sanguis biofilms were significantly affected by both glass-ionomer formulations, the greater reduction being noted on the surface of the fluoride containing GIC. S. sanguis biofilms produced reduction on the surface hardness of the cement equivalent to that seen after immersion in lactic acid at pH 5. This indicates that while S. sanguis biofilm is affected by the GIC, there is also a decrease in hardness of the cement indicating some cement degradation.

Multivariate analysis of surface physico-chemical properties controlling biofilm formation on orthodontic adhesives prior to and after fluoride and chlorhexidine treatment

Biofilm formation on orthodontic adhesives is a serious clinical problem, as it leads to enamel demineralization around fixed orthodontic appliances, often leaving white spot lesions after their removal. The aim of this work was to determine the influence of surface physico-chemical properties of four commonly used orthodontic adhesives (Concise, Fuji ORTHO LC, Ketac Cem mu, and Transbond XT) on early bacterial biofilm formation. In addition, effects of two commercially available mouthrinses (0.05% sodium fluoride and 0.2% chlorhexidine gluconate) on these properties and biofilm formation were determined. Water contact angles on the adhesives decreased after fluoride and chlorhexidine treatment, concurrent with an increase in carbon and a decrease in oxygen surface concentrations, except for Transbond, as determined by X-ray photoelectron spectroscopy. No fluorine was detected on any of the adhesive surfaces after fluoride treatment, while all surfaces showed chlorine after chlorhexidine treatment. Surface roughness of the adhesives measured using three-dimensional optical profilometry was around 4 microm and found not to be a factor governing early biofilm formation. Multiple linear regression analysis indicated that early biofilm formation by Streptococcus sanguis could be explained in a model comprising hydrophobicity and the prevalence of oxygen- and nitrogen-rich components on the adhesive surfaces.

Antibacterial effect of two mineral trioxide aggregate (MTA) preparations against Enterococcus faecalis and Streptococcus sanguis in vitro

The antibacterial effects of gray-colored MTA (GMTA) and white-colored MTA (WMTA) against Enterococcus faecalis and Streptococcus sanguis were assessed in vitro using the tube dilution test. Broth tubes were prepared and divided into experimental and control groups. Aliquots of each of the tested microorganisms were taken from a stock culture and added to each experimental and positive control group. All groups were incubated at 37 degrees C and evaluated for turbidity at 0, 1, 24, 48, and 72-hour time periods. A direct correlation was found between GMTA and WMTA concentrations and their antibacterial effect. Tubes containing GMTA in concentrations of 50, 25, and 12.5 mg/ml did not show E. faecalis growth at any of the time periods tested whereas tubes containing WMTA showed E. faecalis growth at all concentrations and time periods tested. Statistically significant differences were found between tubes containing GMTA in concentrations of 50, 25 and 12.5 mg/ml and tubes containing similar concentrations of WMTA (p < 0.001). Tubes containing GMTA in concentrations of 50, 25, 12.5, 6.25, and 3.12 mg/ml and tubes containing WMTA in concentrations of 50, 25, and 12.5 mg/ml did not show S. sanguis growth at any of the time periods tested. Statistically significant differences were found between tubes containing GMTA in concentrations 6.25 and 3.12 mg/ml and tubes containing similar concentrations of WMTA (p < 0.001). It appears that the susceptibility of E. faecalis and S. sanguis to MTA differed and that GMTA requires lower concentrations than WMTA to exert the same antibacterial effect against each of the microorganisms tested.

Competition and coexistence between Streptococcus mutans and Streptococcus sanguinis in the dental biofilm

The human mucosal surface is colonized by the indigenous microflora, which normally maintains an ecological balance among different species. Certain environmental or biological factors, however, may trigger disruption of this balance, leading to microbial diseases. In this study, we used two oral bacterial species, Streptococcus mutans and Streptococcus sanguinis (formerly S. sanguis), as a model to probe the possible mechanisms of competition/coexistence between different species which occupy the same ecological niche. We show that the two species engage in a multitude of antagonistic interactions temporally and spatially; occupation of a niche by one species precludes colonization by the other, while simultaneous colonization by both species results in coexistence. Environmental conditions, such as cell density, nutritional availability, and pH, play important roles in determining the outcome of these interactions. Genetic and biochemical analyses reveal that these interspecies interactions are possibly mediated through a well-regulated production of chemicals, such as bacteriocins (produced by S. mutans) and hydrogen peroxide (produced by S. sanguinis). Consistent with the phenotypic characteristics, production of bacteriocins and H2O2 are regulated by environmental conditions, as well as by juxtaposition of the two species. These sophisticated interspecies interactions could play an essential part in balancing competition/coexistence within multispecies microbial communities.

[Study of antibacterial effect of Galla Chinensis on the bacteria biofilm in chemostat]

OBJECTIVE

To compare the antibacterial effect of Galla Chinensis with that of chlorhexidine by means of chemostat and provide experimental foundation for caries prevention with Chinese medicine instead of chemicals in future.

METHOD

A multispecies consortium biofilm (BF) model was construted in the chemostat. The growth-inhibition on bacterial biofilm coated on HA was investigated by means of the colony-forming units (CFU). Acid-inhibition was inspected by continual pH-recording in the flow cells. And the profile on the biofilm treated by both experimental medicines was observed with the scanning electromicroscopy (SEM).

RESULT

Both of the experimental medicines could inhibit the growth of the BF bacteria. And Galla Chinensis had no obvious influence on the ecological composing of the BF bacteria. Both of the experimental medicines could inhibit the acid producion of experimental bacteria. But the final pH of Galla Chinensis was lower than that of chlorhexidine. A typical biofilm formed on HA was observed by SEM. Both of Galla chinensis and chlorhexidine could inhibit the production of extracellular matrix and make the BF profile on the surface of the HA clearer and simpler.

CONCLUSION

Galla Chinensis had definite antibacterial effect. No obvious difference is found between Galla Chinensis (4 g x L(-1)) and chlorhexidine (0.5 g x L(-1)). Therefore, it is possible for Chinese medicine to gradually replace the chemical medicine in clinic and it will give a new choice for caries prevention.

Biofilm-specific surface properties and protein expression in oral Streptococcus sanguis

OBJECTIVE

Oral streptococci are primary colonisers of the tooth surface and are abundant in dental plaque biofilms. Bacteria growing in these relatively dense, surface-associated communities are phenotypically quite distinct from their planktonic counterparts. The purpose of the present study was to develop a method to investigate biofilm-specific surface protein expression by Streptococcus sanguis to help provide a better understanding of the critical events in plaque development.

DESIGN

Biofilm cells were grown on the surface of glass beads in a biofilm device fed with mucin-containing artificial saliva. Planktonic cells were grown in continuous culture at approximately the same growth rate. Surface hydrophobicity of biofilm and planktonic cells was determined by hexadecane partitioning, and expression of streptococcal fibronectin adhesin CshA was determined in ELISA using specific antiserum. Antisera raised to glutaraldehyde-fixed whole biofilm or planktonic grown cells were used to screen an expression library of S. sanguis genomic DNA, and isolated clones were sequenced.

RESULTS

Phenotypic analysis of biofilm and planktonic cells confirmed that mode of growth affected surface properties of S. sanguis. Thus, hydrophobicity and CshA expression was significantly elevated in biofilm cells. Library screening with biofilm antiserum yielded 32 recombinant clones representing 21 different S. sanguis proteins involved in adhesion and colonisation, carbohydrate utilisation or bacterial metabolism. In differential analysis of four selected Escherichia coli clones, biofilm antiserum reacted five times stronger than planktonic antiserum with cell-free extracts of clones encoding homologues of CshA and Cna collagen adhesin of Staphylococcus aureus, suggesting that these surface proteins are up-regulated in biofilm cells. In contrast, both antisera reacted equally strongly with cell-free extracts of the remaining two clones (encoding dihydrofolate synthase and an unknown protein).

CONCLUSIONS

The method described represents a useful means for determining bacterial protein expression in biofilms based on a combination of molecular and immunological techniques. Surface expression of putative fibronectin and collagen adhesins was up-regulated in biofilm cells.

Effectiveness of Sodium Hypochlorite in Preventing Inoculation of Periapical Tissues With Contaminated Patency Files

The aim of this study was to analyze the effectiveness of 5.25% sodium hypochlorite (NaOCI) in preventing inoculation of periapical tissues with contaminated patency files. Twenty-eight extracted human permanent teeth with single canals were used in the study. Group I teeth were filled with NaOCl, and #15 stainless steel files contaminated with Streptococcus sanguis (ATCC #10556) were allowed to pass through the NaOCI into the culture medium. The teeth in group II were also filled with NaOCl, but the contaminated files used in group II canals were immersed in NaOCl for 10 s prior to being placed into the canals and cultured. The negative control group used sterile files (0% growth), the first positive control group used contaminated patency files in teeth with empty canals (100% growth), and the second positive control group placed contaminated files into broth next to teeth filled with NaOCl (to evaluate potential chlorine leakage; 100% growth). The experimental results showed no positive growth of S. sanguis for groups I and II, indicating that the NaOCl present in the canal after irrigation was sufficient to kill the test organism.

The acid-tolerant microbiota associated with plaque from initial caries and healthy tooth surfaces

The intent of this study was to compare the inherent acid tolerance of bacteria in samples of dental plaque from tooth sites in subjects with and without initial caries. Plaque was collected from approximal surfaces showing early enamel caries and from healthy tooth surfaces in the same subjects, as well as from enamel surfaces of caries-free individuals. In addition to plating on blood agar, the plaque samples were plated directly on non-selective solid agar medium buffered to pH 7.0, 6.0, 5.5, 5.0, 4.5 and 4.0 to avoid any loss of adaptation to acid during primary isolation of plaque bacteria. The results showed that approximately 50% of the total cultivable plaque microbiota from caries, as well as healthy tooth sites, was able to grow at pH 5.5 and 1% at pH 5.0, pH values regarded as critical for the demineralization of tooth enamel. At pH 5.0, members of the genus Streptococcus were the dominant group, but mutans streptococci accounted for less than half of the streptococcal viable count. The other acid-tolerant streptococcal isolates included Streptococcus anginosus, Streptococcus constellatus, Streptococcus gordinii, Streptococcus intermedius, Streptococcus mitis, Streptococcus oralis, Streptococcus salivarius and SStreptococcus sanguis. Analysis of the results indicated that the mutans streptococci in dental plaque were highly variable with respect to acid tolerance, and that both caries and healthy sites harboured significant numbers of mutans streptococci that were not acid-tolerant.

Reduction of viable bacteria in dentinal tubules treated with clindamycin or tetracycline

AIM

We sought to evaluate and compare the antibacterial effect of clindamycin and tetracycline in bovine dentinal tubules.

METHODS

Dentinal tubules of 32 cylindrical bovine root specimens were infected with Streptococcus sanguis N1. Clindamycin 2% or tetracycline 2% (Ledermix) was placed in the root canal for 1 week. Powder dentin samples obtained from within the canal lumina by using International Standards Organization No. 25 to No. 31 burs were examined for the presence of vital bacteria after the brain-heart infusion plates were inoculated and the colony-forming units were counted. The potent effect of the medicaments was also evaluated through the use of the agar diffusion test.

RESULTS

Heavy bacterial infection was observed in the control bovine root specimens at the layer close to the lumen. This decreased rapidly from layer to layer up to the deepest layer tested (300-400 microm), which contained several hundred colony-forming units. Clindamycin significantly reduced the amount of viable bacteria in each dentin layer compared with the positive control and tetracycline (P <.01). The agar diffusion test, wherein dilutions in increments of 1/3 and 1/9 were used, revealed that both medicaments had antibacterial activity, but clindamycin was significantly better. In the 1/27 dilution, clindamycin had a minor effect and tetracycline had no effect at all.

CONCLUSION

Under the experimental conditions used in this study, the commercial preparations of clindamycin were more effective than those of tetracycline (Ledermix) in the agar diffusion test and clindamycin penetrated into dentinal tubules up to 400 microm. Thus, it has the potential to serve as an effective intracanal medicament in persistent infections when other medicaments fail.

In vitro assay for the screening of the plaque-reducing activity of antimicrobial agents

Bacteria grown in biofilms are less susceptible to antimicrobial agents than planktonic bacteria. One of the most common biofilms in humans is dental plaque. To investigate the antimicrobial activity against dental bacteria grown in biofilms, biofilms were generated with Streptococcus sanguis on hydroxyapatite disks to mimic the tooth surface. After 48 h of aerobic incubation at 37 degrees C in a continuous flow culture, a biofilm consisting of Streptococcus sanguis became visible on the surface of the disks. The disks were removed from the growth chamber and placed in different vessels containing either chlorhexidine digluconate (CAS 55-56-1, 0.1% or 1.0%), polyvinylpyrrolidone iodine (1.5% or 7.5%), or octenidine dihydrochloride (CAS 70775-75-6, 0.05% or 0.1%) for 5 or 30 min. In addition, the antiseptics were applied to the bacterial suspension in the growth chamber. A significant difference was observed in the antimicrobial activity against bacteria in the suspension liquid compared to the bacteria grown in biofilms. The best reduction factors were obtained with chlorhexidine (1.0%, 30 min) for either sessile (3.97 Ig) or planktonic bacteria (> or = 5.58 Ig). Clear relationships between the doses and times of action were found for the assessed agents. Therefore, the authors conclude that the present in vitro assay is a quick and cost-effective model to screen the activity of antimicrobial agents against bacteria grown in biofilms.

Will triclosan in toothpaste select for resistant oral streptococci?

The aims of the study were to determine the in vitro sensitivity of triclosan against viridans streptococci and the impact of triclosan on the normal oral microflora. Nine subjects used a triclosan-containing toothpaste for 2 weeks. Saliva samples were collected on days 0 and 14 and were analyzed quantitatively. The minimum inhibitory concentrations of triclosan and of several antimicrobial agents were determined for the streptococci isolated on days 0 and 14. No major changes occurred in the normal oral microflora during the study period. There were no differences in susceptibility between streptococcal strains collected at days 0 and 14 against triclosan or antimicrobial agents. Short-term use of triclosan has no major impact on normal oral microflora or on streptococcal susceptibility of antimicrobial agents. The effects of long-term use should be evaluated.

In vitro testing of xylitol as an anticariogenic agent

A number of studies involving xylitol chewing gum have demonstrated that xylitol is both noncariogenic and anticariogenic. The ability of xylitol to act as an anticariogenic agent most likely is due to its ability to be transported into caries-causing oral bacteria and inhibiting fermentation either by depleting the cell of high-energy phosphate or by poisoning the glycolytic system. In vitro tests were conducted to determine the concentration of xylitol required to inhibit the growth of three strains of oral streptococcus (S. mutans, S. salivarius, and S. sanguis). All three strains were inhibited significantly at xylitol concentrations of 12.5% and higher; however, only S. mutans was inhibited significantly at a xylitol concentration of 1.56%.

The relationship between odontogenic bacteraemia and orthodontic treatment procedures

The purpose of this research was to estimate the prevalence and intensity of bacteraemia associated with orthodontic treatment procedures. The four procedures investigated were: an upper alginate impression, separator placement, band placement, and adjustment of an archwire on a fixed appliance. Eighty-one children undergoing general anaesthesia (GA) for dento-alveolar surgery related to their orthodontic treatment were randomly allocated to the impression or separator group. A further 61 children, receiving treatment in the Outpatient Department, were included and randomly allocated to the banding or archwire adjustment groups. A cannula was inserted into either the left or right antecubital fossa using an aseptic technique. A baseline 6 ml sample of blood was taken before treatment and a second 6 ml sample was taken 30 seconds after the procedure. There was no significant difference in the number of positive blood cultures between baseline (nine, 23 per cent), and following an upper alginate impression (twelve, 31 per cent); between baseline (twelve, 27 per cent), and placement of a separator (fifteen, 36 per cent); between baseline (nine, 36 per cent), and fitting or placement of a band (eleven, 44 per cent); or between baseline (twelve, 33 per cent), and archwire adjustment (seven, 19.4 per cent). For the separator group only the mean total number of aerobic and anaerobic bacteria combined, isolated from the blood samples (cfu of bacteria per ml of blood), was significantly greater following the placement of a separator (2.2, SD 9.1), compared with baseline (0.9, SD 0.2; P < 0.02). This investigation demonstrates that the only orthodontic treatment procedure that causes a significant bacteraemia is the placement of a separator.

Particulate Bioglass reduces the viability of bacterial biofilms formed on its surface in an in vitro model

45S5 Bioglass is a bioactive implant material which, in its particulate form, is used in the repair of periodontal defects. The surface reactions undergone by this material in an aqueous environment may exert an antibacterial effect that would be beneficial to periodontal surgical treatment. Biofilms of Streptococcus sanguis, an early plaque former, and mixed species biofilms from a salivary inoculum grown under conditions similar to those associated with periodontal implants, were grown on particulate Bioglass in a constant depth film fermenter (CDFF). Control biofilms were grown on inert glass particulates. At sample times of 3, 24 and 48 hours the viability of biofilms of S. sanguis grown on Bioglass was significantly lower than for those grown on inert glass. In the experiments with subgingivally-modelled mixed species biofilms, the total anaerobic counts were significantly lower on Bioglass after 24 and 48 hours, but not 96 or 168 hours, compared to inert glass. Thus, particulate Bioglass has the potential to reduce bacterial colonisation of its surface in vivo, a feature relevant to post-surgical periodontal wound healing.

The effect of tissue molecules on bacterial invasion of dentine

Bacterial invasion of dentinal tubules is a critical step in the pathogenesis of dental caries and pulp and periapical disease. The purpose of this study was to determine the effect some molecules commonly found in saliva and dentinal tubule fluid may have on the bacterial invasion of dentine. The results showed that invasion of Streptococcus gordonii or Enterococcus faecalis cells was inhibited when the bacterial cells were in solution with mucin, immunoglobulin G (IgG) and serum, and this was related to bacterial cell aggregation, as a result of interaction with agglutinins, and/or inhibition of collagen binding. When dentine was soaked in growth media containing fibrinogen, IgG, albumin or serum prior to inoculation, bacterial invasion was inhibited. It is suggested that this may be due to reduced dentine permeability as a consequence of the deposition of the compounds within dentinal tubules.

[The influence of two implant materials on the growth of three subgingival predominant bacteria]

OBJECTIVE

Commercially pure titanium and titanium alloy as dental implants have show impressive clinical results. Despite the high success rates, some implants do fail. Compared to those studies on osseointegration of implants, the information pertaining to their failure is little. Further studies on the relationship between implant material and micro-organism are needed. The purpose of this investigation is to study the effect of two commonly used implant materials Titanium (TA2) and Ti-6AI-4V alloy (TC4) on the growth behaviour of three subgingival predominant bacteria Streptococcus sanguis (S. s), Porphyromanus gingivalis (P. g), Fusobacterium nucleatum (F. n) and their mixture.

METHODS

Under anaerobic condition, bacterial suspensions of S.s, P.g, F.n and their mixture were incubated together with the two implant materials respectively, setting the same bacterial suspensions as controls. After 2, 7 and 14 days, the bacterial growth amount was assayed by means of clone forming unit (CFU) method. The pH value of the bacterial suspension was determined by pH-Meter.

RESULTS

The results showed that there was no difference in amount of bacterial growth or pH value between TA2 group and TC4 group (P > 0.05). There was also no statistically significant change as to the proportion of individual bacteria in bacterial mixture or the pH value of culture suspension.

CONCLUSION

Under the condition of this investigation, the two studies implant materials have no examined influences on the growth of the subgingival bacteria and the pH value of their culture environment.

Antimicrobial activity of four root canal sealers against endodontic pathogens

The antibacterial effects of various types of widely used endodontic sealers have not been compared systematically on facultative or obligate anaerobic endodontic pathogens. The aim of this study was to evaluate the antimicrobial properties of four commonly used endodontic sealers: two epoxy-resin-based sealers (AH26, AH plus), one zinc-oxide eugenol-based sealer (N2), and one calcium hydroxide-based sealer (Sealapex). The testing microbes were four facultative anaerobic species (Streptococcus mutans, Streptococcus sanguis, Escherichia coli, and Staphylococcus aureus) and four obligate anaerobic species (Porphyromonas gingivalis, Porphyromonas endodontalis, Fusobacterium nucleatum, and Prevotella intermedia). The freshly mixed sealers were placed into the prepared wells of agar plates inoculated with the test microorganisms. After varying periods of incubation (2 days for facultative anaerobic species and 7 days for obligate anaerobic species), the zones of growth inhibition were observed and measured. All the sealers were distinctly different from each other in their antimicrobial activity. The sealers showed different inhibitory effects depending on the types and bacterial strains. N2 containing formaldehyde and eugenol proved to be the most effective against the microorganisms. The extreme antimicrobial potency of this root canal sealer must be weighted against its pronounced tissue toxic effect.

The predominant microflora of nursing caries lesions

The predominant microflora recovered from infected dentine of 52 carious teeth from 14 children with nursing caries was determined using both selective and non-selective media for the isolation of specific genera and acidified media (pH 5.2) to isolate the predominant aciduric microorganisms, and compared with the microflora of sound enamel surfaces in caries-free children. Streptococcus mutans formed a significantly greater proportion of the lesion flora while Streptococcus oralis, Streptococcus sanguis and Streptococcus gordonii formed a significantly greater proportion of the plaque flora from sound tooth surfaces. The proportions of Actinomyces naeslundii and Actinomyces odontolyticus were significantly greater in the plaque samples than in the lesion samples. Actinomyces israelii formed 18.2% of the flora from the lesions, but was not isolated from the plaque samples. The proportions of Candida albicans, Lactobacillus spp. and Veillonella spp. were also significantly greater in the carious dentine than in the plaque samples. The most frequently isolated lactobacilli were Lactobacillus casei, Lactobacillus fermentum and Lactobacillus rhamnosus. The predominant aciduric flora was S. oralis, S. mutans and A. israelii and these taxa were also isolated from a similar proportion of the lesions at pH 7.0. Strains of S. mutans, L. casei, L. fermentum and L. rhamnosus isolated from individual carious teeth were genotyped using PCR-based methods. Each species was genotypically heterogeneous and different genotypes were recovered from different carious teeth in the same child. These data indicate that the microflora of lesions in the same child is microbiologically diverse and support a non-specific aetiology for nursing caries in which the physiological characteristics of the infecting flora, not its composition, is the major determinant underlying the disease process.

Cariogenic potential of lactosylfructoside as determined by acidogenicity of oral streptococci in vitro and human dental plaque in situ

The cariogenic potential of lactosylfructoside [O-beta-D-galactopyranosyl-(1-->4)-O-alpha-D-glucopyranosyl-(1<-->2)-beta-D-fructofuranoside] was estimated by experiments on oral streptococci in vitro and human dental plaque in situ. Lactosylfructoside was unable to support growth of the strains of Streptococcus mutans and S. sobrinus used in this study. However, it was able to support growth of strains of S. sanguis, S. mitis and S. oralis. Acid was produced rapidly by cell suspensions of S. oralis ATCC 10557 incubated with lactosylfructoside. Application of 5% w/v solution decreased the pH of human dental plaque. The minimum pH value was below 5.3. The results suggest that lactosylfructoside is as acidogenic as lactose and could be cariogenic if it is consumed frequently and retained for a long period in the mouth.

The ability of direct fluorescence-based, two-colour assays to detect different physiological states of oral streptococci

AIMS

To investigate the ability of six fluorescent-based, two-colour viability assays to detect different physiological growth stages of two oral streptococci species.

METHODS AND RESULTS

The growth of Streptococcus sanguinis and Strep. mutans from 0 to 73 h culture periods was monitored by cell labelling with six mixtures of fluorescent stains, in addition to the growth parameters optical density (O.D.), log values of the total cell counts (log BC ml(-1)) and of the colony-forming units (log cfu ml(-1)).

CONCLUSION

In comparison with the corresponding cfu values as control, the vitality proportions determined by the Syto 9/PI test best reflected the dynamic growth pattern of both test strains. The direct fluorescent-based, two-colour assay Syto 9/PI provides valuable information about microbial viability stages.

SIGNIFICANCE AND IMPACT OF THE STUDY

The detection of viable but non-culturable bacteria requires more precise direct methods such as the fluorescent staining technique presented here, in addition to the classical plate count method.

Antibacterial activity of particulate Bioglass® against supra- and subgingival bacteria

Particulate Bioglass is a bioactive material used in the repair of periodontal defects. This material undergoes a series of surface reactions in an aqueous environment which lead to osseointegration. The aim of this study was to determine whether these reactions exerted an antibacterial effect on a range of oral bacteria. Streptococcus sanguis, Streptococcus mutans and Actinomyces viscosus were suspended in nutrient broth (NB), artificial saliva (AS) or Dulbecco's modified eagle medium plus 10% foetal calf serum (DMEM + 10%FCS), with or without particulate Bioglass. All bacteria showed reduced viability following exposure to Bioglass in all the media after 1 h. This antibacterial effect increased after 3 h. Porphyromonas gingivalis, Fusobacterium nucleatum, Prevotella intermedia and Actinobacillus actinomycetemcomitans were suspended in either BM broth or 40% horse serum (HS) in RPMI. A considerable reduction in viability was observed with all bacteria tested, in both media, compared to inert glass controls. In further experiments it was found that the viability of S. sanguis was significantly reduced following exposure to NB pre-incubated with Bioglass. Additionally, it was found that neutralisation of this highly alkaline solution eliminated the antibacterial effect. Moreover, a solution of NB and NaOH (of equivalent pH) exerted an antibacterial effect of similar magnitude to that of the solution pre-incubated with Bioglass. Thus, particulate Bioglass exerts an antibacterial effect on certain oral bacteria, possibly by virtue of the alkaline nature of its surface reactions. This may reduce bacterial colonisation of its surface in vivo.

Utilization and acid production of beta-galactosyllactose by oral streptococci and human dental plaque

Beta-galactosyllactose is a trisaccharide containing the beta-galactosidic linkage at the nonreducing end. The purpose of this study was to determine whether certain oral streptococci could utilize four kinds of beta-galactosyllactoses. Three of four beta-galactosyllactoses were unable to support growth of the oral streptococci and to be a substrate for producing acid from the cell suspensions and dental plaque. 4'-beta-Galactosyllactose supported growth of Streptococcus sanguis ATCC 35105, ATCC 49298, Streptococcus mitis ATCC 15914, Streptococcus oralis ATCC 35037, ATCC 10557 and Streptococcus milleri 10707 and produced acid from dental plaque. Although beta-galactosidase activities were observed in all the strains, 4'-beta-galactosyllactose could not be used as a carbon source for the growth of mutans streptococci. Enzymes metabolizing 4'-beta-galactosyllactose were induced when S. oralis ATCC 10557 was cultured in medium containing galactose. These results suggested that 4'-beta-galactosyllactose could be as cariogenic as lactose if it is consumed frequently and retained for a long period in the mouth.

The clinical and microbiological effects of systemic ornidazole in sites with and without subgingival debridement in early-onset periodontitis patients

BACKGROUND

The purpose of this study was to evaluate the clinical and microbiological effects of systemic ornidazole (ORN) in sites with or without subgingival debridement in early-onset periodontitis (EOP) patients.

METHODS

Two pooled bacterial samples consisting of 4 sites each (scaled and non-scaled sites) were obtained from 30 individuals exhibiting EOP. All patients received oral hygiene instruction (OHI), supragingival scaling and ORN. Subgingival scaling and root planing (SRP) was carried out only in scaled sites. Bacterial samples were taken at baseline (BL) and 1 week and 2, 6, and 12 months after systemic ornidazole administration (500 mg/bid for 7 days). One more sample was taken at scaled sites, one week after SRP.

RESULTS

One week following SRP (scaled sites) Gram-negative facultative and anaerobic rods were significantly reduced while Gram-positive facultative cocci were significantly increased. After ORN administration, P. gingivalis, P. denticola, P. intermedia, B. forsythus, C. rectus, and S. sputigena were no longer detectable in either scaled or non-scaled sites. A statistically significant long-term (2, 6, and 12 months) reduction of P. gingivalis, P. intermedia, P. loescheii, B. forsythus, and C. rectus and a pronounced increase of S. milleri, S. oralis, and S. sanguis counts in both scaled and non-scaled sites were detected in comparison to baseline. A sustained reduction of bleeding tendency and of probing depth was also observed in both scaled and non-scaled sites.

CONCLUSIONS

ORN combined with SRP effects beneficial shifts in the bacterial population associated with substantial clinical improvement, thereby indicating that ORN is effective adjunct in the treatment of EOP deep periodontal pockets where anaerobic bacteria are predominant.

Sensitization of Actinomyces naeslundii and Streptococcus sanguis in biofilms and suspensions to acid damage by fluoride and other weak acids

Fluoride and other weak acids, such as benzoate, indomethacin, salicylate and sorbate, were found to be sensitizers for acid killing of cells of Actinomyces naeslundii ATCC 19246 and Streptococcus sanguis NCTC 10904 in suspensions or in mono-organism biofilms on glass slides. These bacteria are among the more acid-sensitive organisms from dental plaque and were killed when acidified to pH values between 3.5 and 4.0. Biofilm cells were more resistant than cells in suspensions, especially in terms of the fraction of the initial population surviving acidification. The mechanism for sensitization to acid killing by fluoride and the other weak acids involved enhanced transmembrane transport of protons, reflected by increases in measured proton permeabilities of the cells. Thus, the weak acids thwarted the functions of F(H+)-ATPases in extruding protons and protecting cells against acid damage. Fluoride sensitization of biofilms or cells in suspensions to acid damage occurred rapidly. There was a delay in sensitization of biofilms by indomethacin and higher molecular weight acids which was interpreted in terms of diffusion limitation of sensitizer penetration. Overall, it seemed that weak-acid sensitization to acid killing is a general phenomenon that occurs not just for oral bacteria but also for organisms in food, soil, and other acidified environments.

Investigation of bacteremia following orthodontic debanding

The aim of this study was to investigate the prevalence of bacteremia after orthodontic debanding and debonding. The study group comprised 30 patients (10 men, 20 women). All were treated using the Edgewise technique. Patients with acceptable oral hygiene and fixed appliances in both jaws were included in the study group. Blood samples were obtained using a strict aseptic technique before and after removal of bands and brackets. A 6.6% bacteremia prevalence was observed in both preoperative and postoperative blood samples.

Effects of organic acid anions on growth, glycolysis, and intracellular pH of oral streptococci

Oral streptococci produce large quantities of organic acids as the end-products of carbohydrate fermentation. In an approach to determine if oral streptococci exhibit differential sensitivities to organic acid anions, we determined the effects of formate, lactate, and acetate on intracellular pH maintenance, glycolysis, and growth of Streptococcus mutans and Streptococcus sanguis. Growth was determined as maximum culture optical density in the presence of the organic acid anions at pH 7.1, 6.7, 6.3, and 6.1, and the effects of the anions on glycolytic activity and intracellular pH were determined at pH 7.0 and 5.0. At pH 7.1, the organic acid anions had little effect on growth of either species. At the lower pH values, all of the anions reduced the maximum culture optical density of both species in a pH- and concentration-dependent manner, with S. sanguis being more sensitive to growth inhibition than S. mutans. The organic acid anions had little or no effect on glycolytic activity of either species at pH 7.0. However, all of the organic acid anions tested reduced glycolytic activity at pH 5.0 in a concentration-dependent manner, with S. sanguis being more sensitive than S. mutans. The inhibition of glycolysis could be related to the pKa of the organic acid, with formate and lactate being more inhibitory than acetate. The organic acid anions decreased the intracellular pH of S. mutans and S. sanguis, glycolyzing at an extracellular pH of 5.0, such that the reduction in glycolytic activity caused by the organic acid anions could be directly attributed to the fall in intracellular pH. In conclusion, the production of lactic acid in plaque would not only lower pH, thereby having a disadvantageous effect on less aciduric oral streptococci, such as S. sanguis, but would also increase their sensitivity to the effects of low pH, helping S. mutans to become more dominant.

The transfer of bacteria to, and survival on, dental records

The purpose of this study was to ascertain whether viable bacteria could be transferred from gloves to laboratory cards in dental records and, if so, to determine whether bacteria could survive on the paper. The thumbs and forefingers of two types of glove (Biogel D and Microtouch) were inoculated with Streptococcus sanguis and left for various periods of time. A sterile dental laboratory card was then held with the gloves and the number of bacteria surviving on the card determined after various periods of incubation of the card at room temperature. Bacteria were transferred to the laboratory cards and remained viable for up to 72 h. More viable bacteria were transferred from the Microtouch gloves than from the Biogel D gloves, and this was attributable, in part, to the latter gloves exerting a bactericidal effect. The results demonstrated that bacteria can be transferred from gloves to laboratory cards and that these organisms can remain viable for long periods of time. Dental records may, therefore, represent a possible route of cross-infection.

Efficacy of levofloxacin in the treatment of experimental endocarditis caused by viridans group streptococci

Levofloxacin was investigated against viridans group streptococci in vitro and in rats with experimental aortic endocarditis. The MIC(90)s of levofloxacin and ciprofloxacin for 20 independent isolates of such bacteria were 1 and 8 mg/L, respectively. Rats were infected with two types of organism: either fully susceptible to levofloxacin MIC < or = 0.5 mg/L) or borderline susceptible (MIC 1-2 mg/L). Fully levofloxacin-susceptible bacteria comprised one penicillin-susceptible (MIC 0.004 mg/L) Streptococcus gordonii, and one penicillin-tolerant as well as one intermediate penicillin-resistant (MIC 0.125 mg/L) isogenic strains. Borderline levofloxacin-susceptible bacteria comprised one penicillin-susceptible Streptococcus sanguis and one highly penicillin-resistant Streptococcus mitis (MIC 2 mg/L). Rats were treated for 5 days with drug dosages simulating the following treatments in humans: (i) levofloxacin 500 mg orally once a day (q24 h), (ii) levofloxacin 500 mg orally twice a day (q12 h), (iii) levofloxacin 1 g orally q24 h, (iv) ciprofloxacin 750 mg orally q12 h, and (v) ceftriaxone 2 g iv q24 h. Levofloxacin was equivalent or superior to ceftriaxone, and was successful in treating experimental endocarditis irrespective of penicillin resistance. Nevertheless, standard levofloxacin treatment equivalent to 500 mg q24 h in human was less effective than twice daily 500 mg or once daily 1 g doses against borderline-susceptible organisms. Ciprofloxacin, used as a negative control, was ineffective and selected for resistant isolates. This underlines the importance of MIC determinations when treating severe streptococcal infection with quinolones. In the case of borderline-susceptible pathogens, total daily doses of 1 g of levofloxacin should be considered.

Severe, rapidly progressing peri-implantitis

The replacement of teeth by means of titanium implants is a safe and predictable procedure in most patients. Some studies show that a small number of patients lose the majority of their implants. Unfortunately, it is impossible to identify these patients prior to surgery. It is important to report such cases so that we may, in the future, be able to identify them before surgery. The present case showed a severe and rapid exfoliation of titanium implants. Out of 8 implants inserted in the anterior lower jaw of this patient, only two maintained osseointegration over a 2-year period.

Increased levels of transforming growth factor beta 1 and basic fibroblast growth factor in patients on CAPD: a study during non-infected steady state and peritonitis

Long-term influence of continuous ambulatory peritoneal dialysis (CAPD) on concentrations of transforming growth factor beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) in the peritoneal effluent, and the effect of peritonitis on these cytokines were investigated. TGF-beta1 and bFGF were assayed in effluent samples from dialysate bags collected during the initial week of treatment with CAPD and at 5 months. To determine the effect of peritonitis, dialysate bags were collected on admission to the hospital and on days 3 and 10 and also during non-infected steady state. Serum was drawn prior to infection and on days 1 and 10. TGF-beta1 increased more than threefold during the longitudinal follow-up period, median concentrations of 35 pg/ml to 106 pg/ml (P<0.05). No change in bFGF was seen during this initial 5 months. TGF-beta1 was increased on the first day of peritonitis (median concentration 169 pg/ml) and reached its maximum on day 3 of infection, (median concentration 216 pg/ml) (P<0.05 vs non-infected state, median concentration 39 pg/ml). Basic FGF reached a maximum on day three of infection (median concentration 7.7 pg/ml; P=0.01 vs non-infected state) and then slowly declined. In conclusion, TGF-beta1 is influenced by CAPD treatment per se, and together with bFGF is increased during peritonitis, indicating its importance in the peritoneum and its potential involvement in the development of tissue fibrosis and eventually ultrafiltration failure.

Influence of growth mode and sucrose on susceptibility of Streptococcus sanguis to amine fluorides and amine fluoride-inorganic fluoride combinations

This study evaluated the susceptibility to amine fluorides (AmFs) of planktonic and biofilm cultures of Streptococcus sanguis grown with and without sucrose. Cultures were incubated with AmFs (250 mg of fluoride liter-1) for 1 min. The susceptibility of biofilms was less than that of the planktonic form and was further decreased by growth in the presence of sucrose.

Assessing the relationship between dental disease and coronary heart disease in elderly U.S. veterans

Several recent studies have shown a link between dental disease and coronary heart disease. The authors studied 320 U.S. veterans in a convenience sample to assess the relationship between oral health and systemic diseases among older people. They present cross-sectional data confirming that a statistically significant association exists between a diagnosis of coronary heart disease and certain oral health parameters, such as the number of missing teeth, plaque benzoyl-DL-arginine-naphthylamide test scores, salivary levels of Streptococcus sanguis and complaints of xerostomia. The oral parameters in these subjects were independent of and more strongly associated with coronary heart disease than were recognized risk factors, such as serum cholesterol levels, body mass index, diabetes and smoking status. However, because of the convenience sample studied, these findings cannot be generalized to other populations.

Development of a novel in vitro co-culture system for studying host response to native bacterial antigens

We have developed a novel co-culture system in which murine splenocytes are cultured with live bacteria in the presence of a bacteriostatic antibiotic. Superantigens, like staphylococcal enterotoxin B (SEB) are important factors in bacterial pathogenicity. Research has shown that superantigens affect numerous immune cell types, either directly or indirectly, yet their involvement in pathogenic mechanisms remains poorly defined. In these studies, we utilize the co-culture system to study how superantigen pretreatment affects interferon-gamma (IFN-gamma) production by splenocytes co-cultured with gram-positive bacteria. Streptococcus mutans, S. sanguis and Bacillus subtilis were tested for susceptibility to a panel of antibiotics. Spectinomycin was found to maintain a bacteriostatic state of approximately 10(5) bacteria ml(-1) at optimal concentrations for each bacterial strain. Co-culturing splenocytes with bacteria did not affect splenocyte viability and cultured splenocytes responded to mitogenic stimulation as expected. Two days after SEB pretreatment, isolated splenocytes cultured with either Streptococcus species produced 10-15 times more IFN-gamma than splenocytes from sham-injected controls; however, no differences in CD4+ or CD8+ T cell populations appeared in cultures with or without bacteria. Splenocytes isolated four days after SEB treatment did not produce significant amounts of IFN-gamma in co-culture. Co-cultures containing live bacteria produced four times more IFN-gamma than cultures containing heat-killed bacteria. Splenocytes depleted of natural killer (NK) cells prior to SEB treatment produced 25% less IFN-gamma after 20 h co-culturing with S. mutans. T lymphocytes were identified to be the major producer of IFN-gamma at this time point by intracellular cytokine staining. Apparently SEB exposure primes a response to live bacteria and the response is evident two days after initial exposure. The in vitro co-culture system allows us to observe host responses to bacteria in the context of the multicellular interdependent immune response. With this assay we can more closely 'mimic' in vivo events, particularly immune cell interactions in microfloral environments, to study how the pathogenic effects of superantigens alter this response.

The effect of fluoride on Streptococcus sanguis 7863 IgA1 protease production and activity

Fluoride was found to affect the production of the bacterial IgA1 protease but to have no effect on IgA1 protease activity. The concentrations of fluoride that do affect Streptococcus sanguis growth and IgA1 protease production are higher than those normally seen in vivo under normal circumstances. The concentrations of fluoride in dental plaque following use of a fluoride rinse or dentifrice would be sufficient to reduce Strep. sanguis IgA1 protease production.

Effects of triclosan and triclosan monophosphate on maximum specific growth rates, biomass and hydrolytic enzyme production of Streptococcus sanguis and Capnocytophaga gingivalis in continuous culture

Dental plaque species, Streptococcus sanguis and Capnocytophaga gingivalis, were grown in continuous culture with progressively increasing concentrations of triclosan or its phosphorylated derivative, triclosan monophosphate (TMP). For both organisms, the maximum specific growth rates decreased with increasing concentrations of triclosan or TMP until complete inhibition of growth occurred, which for S. sanguis was at 20 mg/L and 50 mg/L, and for C. gingivalis was at 10 mg/L and 5 mg/L for triclosan and TMP respectively. For both species, biomass levels remained approximately constant or, in some cases, increased slightly at low levels of triclosan or TMP. However, biomass levels then decreased significantly as the triclosan or TMP concentrations approached lethal levels. For S. sanguis, levels of hydrolytic enzymes (acid phosphatase, leucine aminopeptidase and esterase) generally remained approximately constant or increased with increasing concentrations of triclosan or TMP until close to inhibitory levels where enzyme levels were reduced. The ratio of extracellular soluble enzymes to cell-bound enzymes remained constant or increased slightly with increasing levels of triclosan or TMP. For C. gingivalis, production of hydrolytic enzymes (neutral phosphatase, leucine aminopeptidase and trypsin-like protease) remained constant or were reduced when grown with low levels of triclosan and TMP but in some cases increased with higher levels of agents. The proportion of extracellular soluble activity increased significantly when concentrations of agent neared inhibitory levels. The results taken together show that the physiology of cells is significantly altered and that hydrolytic enzymes are released from the cells when these are grown in the presence of increasing concentrations of triclosan or TMP. Enzyme release is more pronounced in the Gram-negative C. gingivalis and indicates that triclosan or TMP can cause membrane perturbation with subsequent release of membrane-located (S. sanguis) or periplasmic (C. gingivalis) hydrolytic enzymes. S. sanguis was more sensitive to triclosan than TMP while C. gingivalis was more sensitive to TMP. This suggests that, in C. gingivalis, TMP may diffuse into the cell wall more easily than triclosan and then be converted to triclosan by phosphatase activity within the cell wall complex, where it may give rise to high localized concentrations and subsequent cell damage.

Thermophysiology of Streptococcus mutans and related lactic-acid bacteria

The temperature ranges for growth of Streptococcus mutans GS-5 and S. sobrinus 6715 were found to be very narrow, from about 30 to 47 degrees C, with optimal growth around 37 degrees C. Thus, the organisms showed little potential to grow in the environment outside of the animal host. In contrast wider ranges were found for Enterococcus hirae, S. rattus and S. sanguis. Detailed study of S. mutans GS-5 showed that energetic coupling, reflected in yields of biomass per mol of glucose utilized, were not greatly affected by changes in temperature within the growth range. However, since glycolysis occurred over a wider temperature range (about 10 to 52 degrees C) than growth, yield values dropped to zero at temperatures above or below the growth range. The temperature range for glycolysis could be related to temperature sensitivity of the phosphoenolypyruvate: sugar phosphotransferase system for sugar uptake. F-ATPases were active over a similar range of temperatures, but with a broad optimal range from about 30 to 50 degrees C. Proton permeability of S. mutans increased steadily with temperature in a manner similar to that of other mesophilic bacteria, such as Escherichia coli. Growth of the bacteria in media supplemented with various fatty acids had major effects on proton permeabilities but the effects were not well reflected by changes in growth or glycolysis of the bacteria. The overall conclusions were that S. mutans is a typical mesophile in relation to membrane and catabolic functions but its narrow temperature range for growth is related to temperature sensitivities of anabolic systems.