Dental plaque formation

Poisson Analysis of Streptococcal Bond-strengthening on Saliva-coated Enamel

The forces responsible for bond-strengthening in initial oral bacterial adhesion are unknown. Since Lifshitz-Van der Waals and electrostatic forces work instantaneously upon approach, it is hypothesized that bond-strengthening is governed by hydrogen bonding. Poisson analysis of adhesion forces observed during the retraction of bacterial probes from surfaces in atomic force microscopy can be used to analyze the nature of the adhesion forces. Streptococcal adhesion forces increased from about −0.7 to −10.3 nN when the contact time between cell surfaces and salivary films on enamel was increased from 0 to 120 sec. Initial and final adhesion forces were stronger for initial colonizers of tooth surfaces ( S. mitis, S. sanguinis) than for later, more cariogenic, strains ( S. sobrinus, S. mutans). Retraction curves after increased contact times showed minor peaks, representative of hydrogen bonds, and Poisson analyses indicated repulsive non-specific forces of around +0.3 nN and slightly more attractive hydrogen-bonding forces (−1.0 nN) for initial than for late colonizers (−0.8 nN).

Bacterial and host interactions of oral streptococci

The oral microbial flora comprises one of the most diverse human-associated biofilms. Its development is heavily influenced by oral streptococci, which are considered the main group of early colonizers. Their initial attachment determines the composition of later colonizers in the oral biofilm and impacts the health or disease status of the host. Thus, the role of streptococci in the development of oral diseases is best described in the context of bacterial ecology, which itself is further influenced by interactions with host epithelial cells, the immune system, and salivary components. The tractability of the oral biofilm makes it an excellent model system for studies of complex, biofilm-associated polymicrobial diseases. Using this system, numerous cooperative and antagonistic bacterial interactions have been demonstrated to occur within the community and with the host. In this review, several recent identified interactions are presented.

Evaluation of bacteria-induced enamel demineralization using optical profilometry

OBJECTIVES

Streptococcus mutans is considered a major causative of tooth decay due to its ability to rapidly metabolize carbohydrates such as sucrose. One prominent excreted end product of sucrose metabolism is lactic acid. Lactic acid causes a decrease in the pH of the oral environment with subsequent demineralization of the tooth enamel. Biologically relevant bacteria-induced enamel demineralization was studied.

METHODS

Optical profiling was used to measure tooth enamel decay with vertical resolution under one nanometer and lateral features with optical resolution as a result of S. mutans biofilm exposure. Comparison measurements were made using AFM.

RESULTS

After 72h of biofilm exposure the enamel displayed an 8-fold increase in the observed roughness average (R(a)), as calculated over the entire measured array. Similarly, the average root mean square (RMS) roughness, R(RMS), of the enamel before and after biofilm exposure for 3 days displayed a 7-fold increase. Further, the direct effect of chemically induced enamel demineralization using biologically relevant organic acids was shown. Optical profiles of the enamel surface after addition of a 30% lactic acid solution showed a significant alteration in the surface topography with a corresponding increase in respective surface roughness statistics. Similar measurements with 10% citric acid over seconds and minutes give insight into the demineralization process by providing quantitative measures for erosion rates: comparing surface height and roughness as metrics.

SIGNIFICANCE

The strengths of optical profilometry as an analytical tool for understanding and analyzing biologically relevant processes such as biofilm induced tooth enamel demineralization were demonstrated.

Pathway analysis for intracellular Porphyromonas gingivalis using a strain ATCC 33277 specific database

BACKGROUND

Porphyromonas gingivalis is a Gram-negative intracellular pathogen associated with periodontal disease. We have previously reported on whole-cell quantitative proteomic analyses to investigate the differential expression of virulence factors as the organism transitions from an extracellular to intracellular lifestyle. The original results with the invasive strain P. gingivalis ATCC 33277 were obtained using the genome sequence available at the time, strain W83 [GenBank: AE015924]. We present here a re-processed dataset using the recently published genome annotation specific for strain ATCC 33277 [GenBank: AP009380] and an analysis of differential abundance based on metabolic pathways rather than individual proteins.

RESULTS

Qualitative detection was observed for 1266 proteins using the strain ATCC 33277 annotation for 18 hour internalized P. gingivalis within human gingival epithelial cells and controls exposed to gingival cell culture medium, an improvement of 7% over the W83 annotation. Internalized cells showed increased abundance of proteins in the energy pathway from asparagine/aspartate amino acids to ATP. The pathway producing one short chain fatty acid, propionate, showed increased abundance, while that of another, butyrate, trended towards decreased abundance. The translational machinery, including ribosomal proteins and tRNA synthetases, showed a significant increase in protein relative abundance, as did proteins responsible for transcription.

CONCLUSION

Use of the ATCC 33277 specific genome annotation resulted in improved proteome coverage with respect to the number of proteins observed both qualitatively in terms of protein identifications and quantitatively in terms of the number of calculated abundance ratios. Pathway analysis showed a significant increase in overall protein synthetic and transcriptional machinery in the absence of significant growth. These results suggest that the interior of host cells provides a more energy rich environment compared to the extracellular milieu. Shifts in the production of cytotoxic fatty acids by intracellular P. gingivalis may play a role in virulence. Moreover, despite extensive genomic re-arrangements between strains W83 and 33277, there is sufficient sequence similarity at the peptide level for proteomic abundance trends to be largely accurate when using the heterologous strain annotated genome as the reference for database searching.

The impact of the stone age diet on gingival conditions in the absence of oral hygiene

BACKGROUND

The objective of this study was to assess the oral microbiota and clinical data in subjects without access to traditional oral hygiene methods and who ate a diet available in the Stone Age.

METHODS

Ten subjects living in an environment replicating the Stone Age for 4 weeks were enrolled in this study. Bleeding on probing (BOP), gingival and plaque indices, and probing depth (PD) were assessed at baseline and at 4 weeks. Microbiologic samples were collected at the mesio-buccal subgingival aspects of all teeth and from the dorsum of the tongue and were processed by checkerboard DNA-DNA hybridization methods.

RESULTS

No subject had periodontitis. Mean BOP decreased from 34.8% to 12.6% (P <0.001). Mean gingival index scores changed from 0.38 to 0.43 (not statistically significant) and mean plaque scores increased from 0.68 to 1.47 (P <0.001). PD at sites of subgingival sampling decreased (mean difference: 0.2 mm; P <0.001). At week 4, the total bacterial count was higher (P <0.001) for 24 of 74 species, including Bacteroides ureolyticus, Eikenella corrodens, Lactobacillus acidophilus, Capnocytophaga ochracea, Escherichia coli, Fusobacterium nucleatum naviforme, Haemophilus influenzae, Helicobacter pylori, Porphyromonas endodontalis, Staphylococcus aureus (two strains), Streptococcus agalactiae, Streptococcus anginosis, and Streptococcus mitis. Bacterial counts from tongue samples were higher at baseline (P <0.001) for 20 species, including Tannerella forsythia (previously T. forsythensis), Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans; serotype a), and Streptococcus spp.

CONCLUSIONS

The experimental gingivitis protocol is not applicable if the diet (e.g., Stone Age) does not include refined sugars. Although plaque levels increased, BOP and PD decreased. Subgingival bacterial counts increased for several species not linked to periodontitis, whereas tongue bacterial samples decreased during the study period.

Activity of panduratin A isolated from Kaempferia pandurata Roxb. against multi-species oral biofilms in vitro

The formation of dental biofilm caused by oral bacteria on tooth surfaces is the primary step leading to oral diseases. This study was performed to investigate the preventive and reducing effects of panduratin A, isolated from Kaempferia pandurata Roxb., against multi-species oral biofilms consisting of Streptococcus mutans, Streptococcus sanguis and Actinomyces viscosus. Minimum inhibitory concentration (MIC) of panduratin A was determined by the Clinical and Laboratory Standards Institute (CLSI) broth microdilution assay. Prevention of biofilm formation was performed on 96-well microtiter plates by coating panduratin A in mucin at 0.5-40 microg/ml, followed by biofilm formation at 37 degrees C for 24 h. The reducing effect on the preformed biofilm was tested by forming the biofilm at 37 degrees C for 24 h, followed by treatment with panduratin A at 0.2-10 microg/ml for up to 60 min. Panduratin A showed a MIC of 1 microg/ml for multi-species strains. Panduratin A at 2 x MIC for 8 h exhibited bactericidal activity against multi-species planktonic cells for 8 h. At 8 x MIC, panduratin A was able to prevent biofilm formation by > 50%. Biofilm mass was reduced by > 50% after exposure to panduratin A at 10 microg/ml for 15 min. Panduratin A showed a dose-dependent effect in preventing and reducing the biofilm. These results suggest that panduratin A is applicable as a natural anti-biofilm agent to eliminate oral bacterial colonization during early dental plaque formation.

The degree of microbiome complexity influences the epithelial response to infection

Background

The human microflora is known to be extremely complex, yet most pathogenesis research is conducted in mono-species models of infection. Consequently, it remains unclear whether the level of complexity of a host's indigenous flora can affect the virulence potential of pathogenic species. Furthermore, it remains unclear whether the colonization by commensal species affects a host cell's response to pathogenic species beyond the direct physical saturation of surface receptors, the sequestration of nutrients, the modulation of the physico-chemical environment in the oral cavity, or the production of bacteriocins. Using oral epithelial cells as a model, we hypothesized that the virulence of pathogenic species may vary depending on the complexity of the flora that interacts with host cells.

Results

This is the first report that determines the global epithelial transcriptional response to co-culture with defined complex microbiota. In our model, human immortalized gingival keratinocytes (HIGK) were infected with mono- and mixed cultures of commensal and pathogenic species. The global transcriptional response of infected cells was validated and confirmed phenotypically. In our model, commensal species were able to modulate the expression of host genes with a broad diversity of physiological functions and antagonize the effect of pathogenic species at the cellular level. Unexpectedly, the inhibitory effect of commensal species was not correlated with its ability to inhibit adhesion or invasion by pathogenic species.

Conclusion

Studying the global transcriptome of epithelial cells to single and complex microbial challenges offers clues towards a better understanding of how bacteria-bacteria interactions and bacteria-host interactions impact the overall host response. This work provides evidence that the degree of complexity of a mixed microbiota does influence the transcriptional response to infection of host epithelial cells, and challenges the current dogma regarding the potential versus the actual pathogenicity of bacterial species. These findings support the concept that members of the commensal oral flora have evolved cellular mechanisms that directly modulate the host cell's response to pathogenic species and dampen their relative pathogenicity.

Characterization of hydrogen peroxide-induced DNA release by Streptococcus sanguinis and Streptococcus gordonii

Extracellular DNA (eDNA) is produced by several bacterial species and appears to contribute to biofilm development and cell-cell adhesion. We present data showing that the oral commensals Streptococcus sanguinis and Streptococcus gordonii release DNA in a process induced by pyruvate oxidase-dependent production of hydrogen peroxide (H(2)O(2)). Surprisingly, S. sanguinis and S. gordonii cell integrity appears unaffected by conditions that cause autolysis in other eDNA-producing bacteria. Exogenous H(2)O(2) causes release of DNA from S. sanguinis and S. gordonii but does not result in obvious lysis of cells. Under DNA-releasing conditions, cell walls appear functionally intact and ribosomes are retained over time. During DNA release, intracellular RNA and ATP are not coreleased. Hence, the release mechanism appears to be highly specific for DNA. Release of DNA without detectable autolysis is suggested to be an adaptation to the competitive oral biofilm environment, where autolysis could create open spaces for competitors to invade. Since eDNA promotes cell-to-cell adhesion, release appears to support oral biofilm formation and facilitates exchange of genetic material among competent strains.

Influence of a model human defensive peroxidase system on oral streptococcal antagonism

Streptococcus is a dominant genus in the human oral cavity, making up about 20 % of the more than 800 species of bacteria that have been identified, and about 80 % of the early biofilm colonizers. Oral streptococci include both health-compatible (e.g. Streptococcus gordonii and Streptococcus sanguinis) and pathogenic strains (e.g. the cariogenic Streptococcus mutans). Because the streptococci have similar metabolic requirements, they have developed defence strategies that lead to antagonism (also known as bacterial interference). S. mutans expresses bacteriocins that are cytotoxic toward S. gordonii and S. sanguinis, whereas S. gordonii and S. sanguinis differentially produce H(2)O(2) (under aerobic growth conditions), which is relatively toxic toward S. mutans. Superimposed on the inter-bacterial combat are the effects of the host defensive mechanisms. We report here on the multifarious effects of bovine lactoperoxidase (bLPO) on the antagonism between S. gordonii and S. sanguinis versus S. mutans. Some of the effects are apparently counterproductive with respect to maintaining a health-compatible population of streptococci. For example, the bLPO system (comprised of bLPO+SCN(-)+H(2)O(2)) destroys H(2)O(2), thereby abolishing the ability of S. gordonii and S. sanguinis to inhibit the growth of S. mutans. Furthermore, bLPO protein (with or without its substrate) inhibits bacterial growth in a biofilm assay, but sucrose negates the inhibitory effects of the bLPO protein, thereby facilitating adherence of S. mutans in lieu of S. gordonii and S. sanguinis. Our findings may be relevant to environmental pressures that select early supragingival colonizers.

The oral microbiota: living with a permanent guest

The oral cavity of healthy individuals contains hundreds of different bacterial, viral, and fungal species. Many of these can associate to form biofilms, which are resistant to mechanical stress or antibiotic treatment. Most are also commensal species, but they can become pathogenic in responses to changes in the environment or other triggers in the oral cavity, including the quality of an individual's personal hygiene. The complexity of the oral microbiome is being characterized through the newly developed tools of metagenomics. How the microbiome of the oral cavity contributes to health and disease is attracting the interest of a growing number of cell biologists, microbiologists, and immunologists.

Proteomics of Porphyromonas gingivalis within a model oral microbial community

BACKGROUND

Porphyromonas gingivalis is a periodontal pathogen that resides in a complex multispecies microbial biofilm community known as dental plaque. Confocal laser scanning microscopy showed that P. gingivalis can assemble into communities in vitro with Streptococcus gordonii and Fusobacterium nucleatum, common constituents of dental plaque. Whole cell quantitative proteomics, along with mutant construction and analysis, were conducted to investigate how P. gingivalis adapts to this three species community.

RESULTS

1156 P. gingivalis proteins were detected qualitatively during comparison of the three species model community with P. gingivalis incubated alone under the same conditions. Integration of spectral counting and summed signal intensity analyses of the dataset showed that 403 proteins were down-regulated and 89 proteins up-regulated. The proteomics results were inspected manually and an ontology analysis conducted using DAVID. Significant decreases were seen in proteins involved in cell shape and the formation of the cell envelope, as well as thiamine, cobalamin, and pyrimidine synthesis and DNA repair. An overall increase was seen in proteins involved in protein synthesis. HmuR, a TonB dependent outer membrane receptor, was up-regulated in the community and an hmuR deficient mutant was deficient in three species community formation, but was unimpaired in its ability to form mono- or dual-species biofilms.

CONCLUSION

Collectively, these results indicate that P. gingivalis can assemble into a heterotypic community with F. nucleatum and S. gordonii, and that a community lifestyle provides physiologic support for P. gingivalis. Proteins such as HmuR, that are up-regulated, can be necessary for community structure.

The two-component system BfrAB regulates expression of ABC transporters in Streptococcus gordonii and Streptococcus sanguinis

The putative two-component system BfrAB is involved in Streptococcus gordonii biofilm development. Here, we provide evidence that BfrAB regulates the expression of bfrCD and bfrEFG, which encode two ATP-binding cassette (ABC) transporters, and bfrH, which encodes a CAAX amino-terminal protease family protein. BfrC and BfrE are ATP-binding proteins, and BfrD, BfrF and BfrG are homologous membrane-spanning polypeptides. Similarly, BfrABss, the BfrAB homologous system in Streptococcus sanguinis, controls the expression of two bfrCD-homologous operons (bfrCDss and bfrXYss), a bfrH-homologous gene (bfrH1ss) and another CAAX amino-terminal protease family protein gene (bfrH2ss). Furthermore, we demonstrate that the purified BfrA DNA-binding domain from S. gordonii binds to the promoter regions of bfrCD, bfrEFG, bfrH, bfrCDss, bfrXYss and bfrH1ss in vitro. Finally, we show that the BfrA DNA-binding domain recognizes a conserved DNA motif with a consensus sequence of TTTCTTTAGAAATATTTTAGAATT. These data suggest, therefore, that S. gordonii BfrAB controls biofilm formation by regulating multiple ABC-transporter systems.

Phytotherapeutic prevention of dental biofilm formation

The antimicrobial and biofilm formation preventive properties of Mentha piperita and Rosmarinus officinalis essential oils and chlorhexidine were assessed against Streptococcus mutans and Streptococcus pyogenes. 26 and 20 compounds were identified by GC and GC-MS analysis in hydrodistilled oils from M. piperita and R. officinalis, respectively. The minimal bactericidal concentrations (MBC) of the M. piperita and R. officinalis oils and chlorhexidine were (6000, 2000, 8000 ppm) and (1000, 4000, 1000 ppm) for S. mutans and S. pyogenes, respectively. The decimal reduction time (D) of S. mutans exposed to the oils at their MBC levels was 2.8 min while chlorhexidine showed a longer time. The D values of S. pyogenes on exposure to the MBC levels of M. piperita and R. officinalis oils and of chlorhexidine were 2.14, 4.28 and 2.8 min, indicating a higher efficacy of M. piperita oil. Biofilm formation was performed by growing S. mutans culture with and without essential oils in LB medium in polystyrene tubes. In vitro biofilm inhibitory properties were in the order M. piperita > R. officinalis > chlorhexidine. In vivo experiments on the antibiofilm properties revealed that all concentrations of the oils were significantly (p < 0.001) more effective than chlorhexidine. In conclusion, essential oils may be considered as safe agents in the development of novel antibiofilm agents.

Adhesion of oral streptococci to all-ceramics dental restorative materials in vitro

In recent years, patients have benefited from the development of better and more esthetic materials, including all-ceramics dental restorative materials. Dental plaque formation on teeth and restorative materials plays an important role in the pathogenesis of oral diseases. This study investigates initial adhesion of stationary phase streptococcal species to different all-ceramics dental restorative materials. The saliva-coated materials were incubated with the bacteria for 1 h in an in vitro flow chamber which mimics environmental conditions in the oral cavity. Number and vitality of adhering bacteria were determined microscopically after staining. Surface roughness and the composition of the materials had no distinctive influence on bacterial adhesion. However, S. mutans and S. sobrinus adhered about tenfold less numerous to all materials than the other streptococcal species. Further, there was a correlation between bacterial vitality and materials' glass content. The results showed that early plaque formation was influenced predominantly by the presence of the salivary pellicle rather than by material dependent parameters whereas the composition of the all-ceramics appeared to have influenced the percentage of viable cells during the adhesion process. This presented in vitro technique may provide a useful model to study the influence of different parameters on adherence of oral streptococcal species.

Effects of Low-energy Shock Waves on Oral Bacteria

We have recently demonstrated that extracorporeal shock-wave therapy (ESWT) is effective in promoting the healing of dermal wounds and in regenerating alveolar bone lost through periodontal disease. The objective of the present study was to determine any antibacterial effect of ESWT on oral bacteria. Monoculture suspensions of 6 bacterial species were treated with 100 to 500 pulses of ESWT at energy flux densities (EFD) of 0.12 mJ/mm2, 0.22 mJ/mm2, and 0.3 mJ/mm2. Following treatment, aliquots were plated for viability determination and compared with untreated controls. ESWT showed a significant microbicidal effect for Streptococcus mutans and an unencapsulated strain of Porphyromonas gingivalis following as few as 100 pulses at 0.3 mJ/mm2 (p ≤ 0.001). In addition, a significant disruption of bacterial aggregates was observed at lower EFDs. No significant reduction in viability was observed for all other bacteria at EFDs and pulses tested (p > 0.05). These findings suggest that low-energy ESWT may be bactericidal for selected oral bacteria.

A new paradigm in the periodontal disease progression: gingival connective tissue remodeling with simultaneous collagen degradation and fibers thickening

Bacterial dental plaque is considered to be the main cause of periodontal diseases, but progression of the disease is also related to the host inflammatory response. The earliest affected tissue is the gingiva, but the specific mechanisms involved in the onset of this condition remain unclear. Frequently, collagen degradation is pointed as the main marker of periodontal disease progression, but the organization of the fibers in the gingival tissue is still unknown. The aim of the present study was to investigate the gingival extracellular matrix in a model of ligature-induced periodontal disease. Analysis of the microbiota indicated a progressive increase in the ratio of Gram-negative/Gram-positive microorganisms. There was no difference in the organization of reticulin fibers next to the epithelial basement membrane, whereas the arrangement of collagen fibers in the gingival connective tissue was significantly affected. Animals with inflammation presented a reduction of 35% in the total area occupied by collagen fibers. However, these fibers were thicker and more densely packed. These alterations involve type I, type III and type VI collagens as determined by immunohistochemistry. The results demonstrated the occurrence of marked reorganization of the gingival extracellular matrix in response to the inflammatory process, indicating a new paradigm in the periodontal disease progression: collagen degradation and fibers thickening, simultaneously.

Distribution of Cells between Solid/Liquid and Liquid/Liquid Interfaces

The use of aqueous two-phase systems (ATPSs) and each system's individual phase-forming species to prevent Streptococcus sanguis attachment onto hydroxyapatite discs was explored. The strategy that we followed was to attach the cells to a solid surface in the presence of an additional interface. Conditions under which, simultaneously, the phase-forming species form two phases and the cells proliferate were identified. Growth curves were constructed in the presence of various polymers and salts commonly used to prepare ATPSs. Several aqueous two-phase systems were selected such that bacterial growth was comparable to that observed in pure medium. Cells were allowed to attach to hydroxyapatite discs for 7 days in the presence of varying concentrations of media, media with polymer, media with salt, and media with ATPS. Streptococcus sanguis attachment to the disks was evaluated by scanning electron microscopy. The addition of a PEG/Na(2)SO(4) ATPS to high concentrations of yeast-tryptone (YT) media (>65%) and of a PEG/MgSO(4) ATPS to nutrient-limited media reduces surface coverage of S. sanguis to less than 10%. Comparison of the attachment levels for the systems containing PEG/Na(2)SO(4) to media containing the individual phase-forming species and to the YT reference systems indicated that nutrient availability did not affect attachment.

Binding of the Streptococcus gordonii DL1 surface protein Hsa to the host cell membrane glycoproteins CD11b, CD43, and CD50

Infective endocarditis is frequently attributed to oral streptococci. The mechanisms of pathogenesis, however, are not well understood, although interaction between streptococci and phagocytes are thought to be very important. A highly expressed surface component of Streptococcus gordonii, Hsa, which has sialic acid-binding activity, contributes to infective endocarditis in vivo. In the present study, we found that S. gordonii DL1 binds to HL-60 cells differentiated into monocytes, granulocytes, and macrophages. Using a glutathione S-transferase (GST) fusion to the NR2 domain, which is the sialic acid-binding region of Hsa, we confirmed that the Hsa NR2 domain also binds to differentiated HL-60 cells. To identify which sialoglycoproteins on the surface of differentiated HL-60 cells are receptors for Hsa, intrinsic membrane proteins were assessed by bacterial overlay and far-Western blotting. S. gordonii DL1 adhered to 100- to 150-kDa proteins, a reaction that was abolished by neuraminidase treatment. These sialoglycoproteins were identified as CD11b, CD43, and CD50 by GST pull-down assay and immunoprecipitation with each specific monoclonal antibody. These data suggest that S. gordonii DL1 Hsa specifically binds to three glycoproteins as receptors and that this interaction may be the initial bacterial binding step in infective endocarditis by oral streptococci.

Blocking of bacterial biofilm formation by a fish protein coating

Bacterial biofilm formation on inert surfaces is a significant health and economic problem in a wide range of environmental, industrial, and medical areas. Bacterial adhesion is generally a prerequisite for this colonization process and, thus, represents an attractive target for the development of biofilm-preventive measures. We have previously found that the preconditioning of several different inert materials with an aqueous fish muscle extract, composed primarily of fish muscle alpha-tropomyosin, significantly discourages bacterial attachment and adhesion to these surfaces. Here, this proteinaceous coating is characterized with regards to its biofilm-reducing properties by using a range of urinary tract infectious isolates with various pathogenic and adhesive properties. The antiadhesive coating significantly reduced or delayed biofilm formation by all these isolates under every condition examined. The biofilm-reducing activity did, however, vary depending on the substratum physicochemical characteristics and the environmental conditions studied. These data illustrate the importance of protein conditioning layers with respect to bacterial biofilm formation and suggest that antiadhesive proteins may offer an attractive measure for reducing or delaying biofilm-associated infections.

Inhibition of Experimental Periodontitis by a Topical Boron-based Antimicrobial

AN0128 is a boron-containing compound with antibacterial and anti-inflammatory properties. To test its potential effectiveness in treating periodontal disease, we induced experimental periodontitis in the rat by placing ligatures and assessed the impact of AN0128 and positive and negative controls by micro-CT and histologic measurements. The formation of an inflammatory infiltrate was measured in hematoxylin-and-eosin-stained sections. Daily application of AN0128 (1%) compared with controls reduced bone loss by 38 to 44% (P < 0.05), while vehicle alone had no effect (P > 0.05). The reduction in bone loss with AN0128 was similar to that achieved with a NSAID, ketorolac, and Total toothpaste containing triclosan. AN0128 also reduced the level of gingival inflammation 42% compared with the ligature only (P < 0.05), whereas vehicle alone had no effect (P > 0.05). The results indicate that AN0128 significantly reduces the formation of an inflammatory infiltrate and reduces bone loss, measured histologically and by micro-CT.

Adhesion ofStreptococcus sanguinis to glass surfaces measured by isothermal microcalorimetry (IMC)

Bacterial adhesion is the first step in the development of the oral biofilm, called dental plaque. Plaque is the cause of caries, periodontal diseases, and periimplantitis. Investigations of dental plaque, including bacterial adhesion, employ various in vivo and in vitro models using microscopic methods. Microcalorimetry offers another direct approach. The model organism Streptococcus sanguinis is one of the first colonizers adhering to the saliva-coated human tooth surfaces or dental materials within minutes after tooth cleaning. TAM III thermostats, equipped with microcalorimeters, were used for isothermal microcalorimetric (IMC) measurements of heat production as a function of time, expressed by power-time (p-t) curves. Continuous measurements of heat production of growing S. sanguinis cells showed their overall metabolic activity and were highly reproducible. For the adhesion experiments the bacteria were allowed to adhere to different amounts of glass beads. Growing S. sanguinis cells produced a characteristic p-t curve with a maximum of 500 microW at 4.5 h when reaching 10(9) cells ml(-1). The same number of stationary S. sanguinis cells, suspended in PBS produced only approximately 30 microW at 0.5 h due to adhesion. But the amount of heat increased with available glass surface area, indicating that a portion of the heat of adhesion was measured. Similar results were obtained with stationary S. sanguinis cells suspended in human saliva. This study shows that microcalorimetric evaluation of initial bacterial adhesion is indeed possible and may become a rapid, reproducible screening method to study adhesion of different bacteria to different dental materials or to modified surfaces.

Role of the Clp system in stress tolerance, biofilm formation, and intracellular invasion in Porphyromonas gingivalis

Clp proteases and chaperones are ubiquitous among prokaryotes and eukaryotes, and in many pathogenic bacteria the Clp stress response system is also involved in regulation of virulence properties. In this study, the roles of ClpB, ClpC, and ClpXP in stress resistance, homotypic and heterotypic biofilm formation, and intracellular invasion in the oral opportunistic pathogen Porphyromonas gingivalis were investigated. Absence of ClpC and ClpXP, but not ClpB, resulted in diminished tolerance to high temperatures. Response to oxidative stress was not affected by the loss of any of the Clp proteins. The clpC and clpXP mutants demonstrated elevated monospecies biofilm formation, and the absence of ClpXP also enhanced heterotypic P. gingivalis-Streptococcus gordonii biofilm formation. All clp mutants adhered to gingival epithelial cells to the same level as the wild type; however, ClpC and ClpXP were found to be necessary for entry into host epithelial cells. ClpB did not play a role in entry but was required for intracellular replication and survival. ClpXP negatively regulated the surface exposure of the minor fimbrial (Mfa) protein subunit of P. gingivalis, which stimulates biofilm formation but interferes with epithelial cell entry. Collectively, these results show that the Clp protease complex and chaperones control several processes that are important for the colonization and survival of P. gingivalis in the oral cavity.

Real-time monitoring of the development and stability of biofilms of Streptococcus mutans using the quartz crystal microbalance with dissipation monitoring

Quartz crystal microbalance with dissipation monitoring (QCM-D) was used for continuous in-situ monitoring of cell attachment and growth of Streptococcus mutans as biofilms. Cell attachment and proliferation were monitored within an overnight period of 20 h. Biofilms generated using a 'continuous flow' method had a greater mass and were more dissipative (more viscoelastic) than those established using an 'attach and flow' strategy. Cell numbers (as colony forming units, c.f.u.) in biofilms formed inside the QCM-D device after a 2-h attachment phase and during a 20-h growth period could be related to frequency (f) changes. The percentage surface coverage on the QCM-D crystals by bacteria was estimated using the surface analysis features of the atomic force microscope and image analysis software. Both mean percentage coverage and c.f.u increased after growth of S. mutans. The energy losses displayed by the increases in the dissipative factor (D) indicated an increase in 'softness' of the attached cells. The ratio of D/f was used to provide information of the way in which viscoelasticity changed per unit mass. Flow conditions over the cells on the surface appeared to be important in creating biofilms of a greater complexity and stability and the QCM-D enabled properties of cells during attachment and binding, proliferation and removal to be monitored continuously.

Bacterial colonization immediately after installation on oral titanium implants

BACKGROUND

Information on bacterial colonization immediately after dental implant insertion is limited.

AIMS

(1) To assess the early colonization on titanium implants immediately after placement and throughout the first 12 post-surgical weeks, (2) to compare the microbiota at interproximal subgingival implant and adjacent tooth sites.

MATERIAL AND METHODS

Subgingival plaque samples from implant and neighbouring teeth were studied by checkerboard DNA-DNA hybridization before surgery, 30 min after implant placement, and 1, 2, 4, 8, and 12 weeks after surgery.

RESULTS

Comparing bacterial loads at implant sites between 30 min after placement with 1-week data showed that only the levels of Veillonella parvula (P<0.05) differed with higher loads at week 1 post-surgically. Week 12 data demonstrated significantly higher bacterial loads for 15/40 species at tooth sites compared with pre-surgery (P-values varying between 0.05 and 0.01). Between the period immediately after surgery and 12 weeks at implant sites, 29/40 species was more commonly found at 12 weeks. Included among these bacteria at implant sites were Porphyromonas gingivalis (P<0.05), Tannerella forsythia, (P<0.01), and Treponema denticola (P<0.001). Immediately post-surgery 5.9% of implants, and 26.2% of teeth, and at week 12, 15% of implants, and 39.1% of teeth harbored Staphylococcus aureus. Comparing tooth and implant sites, significantly higher bacterial loads were found at tooth sites for 27/40 species after 30 min following implant placement. This difference increased to 35/40 species at 12 weeks post-surgically.

CONCLUSIONS

Bacterial colonization occurred within 30 min after implant placement. Early colonization patterns differed between implant and tooth surfaces.

Interaction of salivary alpha-amylase and amylase-binding-protein A (AbpA) of Streptococcus gordonii with glucosyltransferase of S. gordonii and Streptococcus mutans

Background

Glucosyltransferases (Gtfs), enzymes that produce extracellular glucans from dietary sucrose, contribute to dental plaque formation by Streptococcus gordonii and Streptococcus mutans. The alpha-amylase-binding protein A (AbpA) of S. gordonii, an early colonizing bacterium in dental plaque, interacts with salivary amylase and may influence dental plaque formation by this organism. We examined the interaction of amylase and recombinant AbpA (rAbpA), together with Gtfs of S. gordonii and S. mutans.

Results

The addition of salivary alpha-amylase to culture supernatants of S. gordonii precipitated a protein complex containing amylase, AbpA, amylase-binding protein B (AbpB), and the glucosyltransferase produced by S. gordonii (Gtf-G). rAbpA was expressed from an inducible plasmid, purified from Escherichia coli and characterized. Purified rAbpA, along with purified amylase, interacted with and precipitated Gtfs from culture supernatants of both S. gordonii and S. mutans. The presence of amylase and/or rAbpA increased both the sucrase and transferase component activities of S. mutans Gtf-B. Enzyme-linked immunosorbent assay (ELISA) using anti-Gtf-B antibody verified the interaction of rAbpA and amylase with Gtf-B. A S. gordonii abpA-deficient mutant showed greater biofilm growth under static conditions than wild-type in the presence of sucrose. Interestingly, biofilm formation by every strain was inhibited in the presence of saliva.

Conclusion

The results suggest that an extracellular protein network of AbpA-amylase-Gtf may influence the ecology of oral biofilms, likely during initial phases of colonization.

Efficacy of the de novo-derived antimicrobial peptide WLBU2 against oral bacteria

The efficacy of a novel synthetic antimicrobial peptide (WLBU2) was evaluated against three oral microorganisms (grown planktonically): Streptococcus gordonii, Fusobacterium nucleatum, and Porphyromonas gingivalis. WLBU2 killed all three species, with F. nucleatum being the most susceptible. WLBU2 also reduced the bacterial burden of S. gordonii and F. nucleatum biofilms.

Paenibacillus strain MP-1: a new source of mutanase

A mutan-degrading bacterium, closely related to Paenibacillus curdlanolyticus, was isolated from soil. It produced 0.4 U mutanase ml(-1 )in 2 days in shake-flask cultures when bacterial mutan was the sole carbon source. Mutanase activity was optimal at pH 6.2 and 45 degrees C over 1 h and was stable between pH 5.8 and 12 at 4 degrees C for 24 h and up to 40 degrees C for 1 h. Mutan produced by Streptococcus mutans was rapidly hydrolyzed by this enzyme. The hydrolysis of mutan (1 g l(-1)) resulted in 17% saccharification over 2 h and, at the same time, glucan was entirely solubilized.

Gingival epithelial cell transcriptional responses to commensal and opportunistic oral microbial species

Transcriptional profiling and ontology tools were utilized to define the biological pathways of gingival epithelial cells modulated by coculture with the oral commensal Streptococcus gordonii and the opportunistic commensal Fusobacterium nucleatum. Overall, F. nucleatum and S. gordonii perturbed the gingival epithelial cell transcriptome much less significantly than the oral pathogens Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans perturbed the transcriptome, indicating that there was a greater degree of host adaptation by the commensal species (M. Handfield, J. J. Mans, G. Zheng, M. C. Lopez, S. Mao, A. Progulske-Fox, G. Narasimhan, H. V. Baker, and R. J. Lamont, Cell. Microbiol. 7:811-823, 2005). The biological pathways significantly impacted by F. nucleatum and S. gordonii included the mitogen-activated protein kinase (MAPK) and Toll-like receptor signaling pathways. Differential regulation of GADD45 and DUSP4, key components of the MAPK pathway, was confirmed at the protein level by Western blotting. Modulation of the MAPK pathway is likely to affect host cell proliferation and differentiation. In addition, both the MAPK and Toll-like receptor pathways ultimately converge on cytokine gene expression. An enzyme-linked immunosorbent assay of secreted interleukin-6 (IL-6) and IL-8 demonstrated that F. nucleatum induced production of these cytokines, whereas S. gordonii inhibited secretion from the epithelial cells. Stimulation of secretion of proinflammatory cytokines from epithelial cells may reflect the invasive phenotype of F. nucleatum and contribute to the greater pathogenic potential of F. nucleatum than of S. gordonii.

Genome of the opportunistic pathogen Streptococcus sanguinis

The genome of Streptococcus sanguinis is a circular DNA molecule consisting of 2,388,435 bp and is 177 to 590 kb larger than the other 21 streptococcal genomes that have been sequenced. The G+C content of the S. sanguinis genome is 43.4%, which is considerably higher than the G+C contents of other streptococci. The genome encodes 2,274 predicted proteins, 61 tRNAs, and four rRNA operons. A 70-kb region encoding pathways for vitamin B(12) biosynthesis and degradation of ethanolamine and propanediol was apparently acquired by horizontal gene transfer. The gene complement suggests new hypotheses for the pathogenesis and virulence of S. sanguinis and differs from the gene complements of other pathogenic and nonpathogenic streptococci. In particular, S. sanguinis possesses a remarkable abundance of putative surface proteins, which may permit it to be a primary colonizer of the oral cavity and agent of streptococcal endocarditis and infection in neutropenic patients.

Streptococcus gordonii Hsa environmentally constrains competitive binding by Streptococcus sanguinis to saliva-coated hydroxyapatite

Competition between pioneer colonizing bacteria may determine polymicrobial succession during dental plaque development, but the ecological constraints are poorly understood. For example, more Streptococcus sanguinis than Streptococcus gordonii organisms are consistently isolated from the same intraoral sites, yet S. gordonii fails to be excluded and survives as a species over time. To explain this observation, we hypothesized that S. gordonii could compete with S. sanguinis to adhere to saliva-coated hydroxyapatite (sHA), an in vitro model of the tooth surface. Both species bound similarly to sHA, yet 10- to 50-fold excess S. gordonii DL1 reduced binding of S. sanguinis SK36 by 85 to >95%. S. sanguinis, by contrast, did not significantly compete with S. gordonii to adhere. S. gordonii competed with S. sanguinis more effectively than other species of oral streptococci and depended upon the salivary film on HA. Next, putative S. gordonii adhesins were analyzed for contributions to interspecies competitive binding. Like wild-type S. gordonii, isogenic mutants with mutations in antigen I/II polypeptides (sspAB), amylase-binding proteins (abpAB), and Csh adhesins (cshAB) competed effectively against S. sanguinis. By contrast, an hsa-deficient mutant of S. gordonii showed significantly reduced binding and competitive capabilities, while these properties were restored in an hsa-complemented strain. Thus, Hsa confers a selective advantage to S. gordonii over S. sanguinis in competitive binding to sHA. Hsa expression may, therefore, serve as an environmental constraint against S. sanguinis, enabling S. gordonii to persist within the oral cavity, despite the greater natural prevalence of S. sanguinis in plaque and saliva.

The effect of mouthrinses against oral microorganisms

This paper reviews the benefits of the use of antimicrobial mouthrinses for controlling dental biofilm. It is currently known that the human oral cavity is inhabited by approximately 600 to 700 different species of microorganisms, including bacteria, fungi and viruses, organized in biofilms. Biofilm accumulation represents the principal etiologic agent of oral diseases including caries and periodontal diseases. For that reason, prevention of biofilm accumulation has been shown to be associated with the control of diseases. Patient motivation and oral hygiene instruction are claimed to be a major factor influencing the degree of biofilm control. Therefore, mechanical home-care methods, including toothbrushing and flossing, represent the best way for patients to remove biofilm. For many patients, however, the elimination of all biofilm present in the oral cavity through home-care methods could be tedious and time-consuming. Additionally, some local conditions, including malpositioned teeth, presence of bridge-work or orthodontic appliances, among others, may render the mechanical control of biofilm especially difficult. Chemotherapeutic agents, including mouthrinses, could have a key role as adjuncts to daily home care, preventing and controlling supragingival plaque, gingivitis and oral malodor. Indeed, according to the ADA, the active ingredients of mouthwashes must demonstrate a therapeutic effect in vivo and in vitro to be classified as drugs. Several studies included in the present review have demonstrated the effectiveness of mouthrinses containing active ingredients such as chlorhexidine and essential oils in preventing and controlling both supragingival plaque and gingivitis, especially when used adjunctively to regular toothbrushing and flossing procedures.

Structural characterization of peptide-mediated inhibition of Porphyromonas gingivalis biofilm formation

Porphyromonas gingivalis is a periodontal pathogen whose primary niche is the anaerobic environment of subgingival dental plaque, but initial colonization of the oral cavity is likely to occur on supragingival surfaces that already support robust biofilm communities. Our studies have shown that P. gingivalis adheres to Streptococcus gordonii through interaction of the minor fimbrial antigen Mfa1 with a specific region of the streptococcal SspB polypeptide (residues 1167 to 1193) designated BAR. We show that a synthetic peptide comprising the BAR sequence potently inhibits P. gingivalis adherence to S. gordonii (50% inhibitory concentration = 1.3 microM) and prevents the development of P. gingivalis biofilms. However, a retroinverso peptide that possessed the same side chain topology as that of BAR was inactive, suggesting that interactions of Mfa1 with the peptide backbone of BAR are important for binding. A conformationally constrained analog of BAR inhibited P. gingivalis adherence and biofilm formation but at a lower specific activity than that of BAR. Therefore, to further define the structural features of the Mfa1-BAR interaction, we functionally screened combinatorial libraries of BAR in which active site residues (Asn1182, Thr1184, and Val1185) were replaced with each of the 19 common amino acids. Peptides containing positively charged amino acids at position 1182 or hydrophobic residues at position 1185 bound P. gingivalis more efficiently than did control peptides containing Asn and Val at these positions, suggesting that electrostatic and hydrophobic interactions may contribute to Mfa1-SspB binding. In contrast, replacement of Pro or Gly at these positions was detrimental to adherence, suggesting that perturbation of the BAR secondary structure influences activity. The net effect of substitutions for Thr1184 was less pronounced either positively or negatively than that at the other sites. These results define physicochemical characteristics of the interacting interface of Mfa1 and SspB and suggest that peptides or peptidomimetics with greater specific inhibitory activity than that of BAR can be developed. These compounds may represent potential therapeutics that target some of the first molecular interactions that allow P. gingivalis to colonize the oral cavity.

Porphyromonas gingivalis genes involved in community development with Streptococcus gordonii

Porphyromonas gingivalis, one of the causative agents of adult periodontitis, develops biofilm microcolonies on substrata of Streptococcus gordonii but not on Streptococcus mutans. P. gingivalis genome microarrays were used to identify genes differentially regulated during accretion of P. gingivalis in heterotypic biofilms with S. gordonii. Thirty-three genes showed up- or downregulation by array analysis, and differential expression was confirmed by quantitative reverse transcription-PCR. The functions of the regulated genes were predominantly related to metabolism and energy production. In addition, many of the genes have no current known function. The roles of two upregulated genes, ftsH (PG0047) encoding an ATP-dependent zinc metallopeptidase and ptpA (PG1641) encoding a putative tyrosine phosphatase, were investigated further by mutational analysis. Strains with mutations in these genes developed more abundant biofilms with S. gordonii than the parental strain developed. ftsH and ptpA may thus participate in a regulatory network that constrains P. gingivalis accumulation in heterotypic biofilms. This study provided a global analysis of P. gingivalis transcriptional responses in an oral microbial community and also provided insight into the regulation of heterotypic biofilm development.

Adherence and internalization of Streptococcus gordonii by epithelial cells involves beta1 integrin recognition by SspA and SspB (antigen I/II family) polypeptides

Streptococcus gordonii is a commensal bacterium that colonizes the hard and soft tissues present in the human mouth and nasopharynx. The cell wall-anchored polypeptides SspA and SspB expressed by S. gordonii mediate a wide range of interactions with host proteins and other bacteria. In this article we have determined the role of SspA and SspB proteins, which are members of the streptococcal antigen I/II (AgI/II) adhesin family, in S. gordonii adherence and internalization by epithelial cells. Wild-type S. gordonii DL1 expressing AgI/II polypeptides attached to and was internalized by HEp-2 cells, whereas an isogenic AgI/II- mutant was reduced in adherence and was not internalized. Association of S. gordonii DL1 with HEp-2 cells triggered protein tyrosine phosphorylation but no significant actin rearrangement. By contrast, Streptococcus pyogenes A40 showed 50-fold higher levels of internalization and this was associated with actin polymerization and interleukin-8 upregulation. Adherence and internalization of S. gordonii by HEp-2 cells involved beta1 integrin recognition but was not fibronectin-dependent. Recombinant SspA and SspB polypeptides bound to purified human alpha5beta1 integrin through sequences present within the NAV (N-terminal) region of AgI/II polypeptide. AgI/II polypeptides blocked interactions of S. gordonii and S. pyogenes with HEp-2 cells, and S. gordonii DL1 cells expressing AgI/II proteins inhibited adherence and internalization of S. pyogenes by HEp-2 cells. Conversely, S. gordonii AgI/II- mutant cells did not inhibit internalization of S. pyogenes. The results suggest that AgI/II proteins not only promote integrin-mediated internalization of oral commensal streptococci by host cells, but also potentially influence susceptibility of host tissues to more pathogenic bacteria.

Human T-cell responses to oral streptococci in human PBMC-NOD/SCID mice

We investigated cellular and humoral immune responses to oral biofilm bacteria, including Streptococcus mutans, Streptococcus anginosus, Streptococcus sobrinus, and Streptococcus sanguinis, in NOD/SCID mice immunized with human peripheral blood mononuclear cells (hu-PBMC-NOD/SCID mice) to explore the pathogenicity of each of those organisms in dental and oral inflammatory diseases. hu-PBMC-NOD/SCID mice were immunized by intraperitoneal injections with the whole cells of the streptococci once a week for 3 weeks. FACS analyses were used to determine the percentages of various hu-T cell types, as well as intracellular cytokine production of interleukin-4 and interferon-gamma. Serum IgG and IgM antibody levels in response to the streptococci were also determined by enzyme-linked immunosorbent assay. S. anginosus induced a significant amount of the proinflammatory cytokine interferon-gamma in CD4(+) and CD8(+) T cells in comparison with the other streptococci. However, there was no significant differences between the streptococci in interleukin-4 production by CD4(+) and CD8(+) T cells after inoculation. Further, S. mutans significantly induced human anti-S. mutans IgG, IgG(1), IgG(2), and IgM antibodies in comparison with the other organisms. In conclusion, S. anginosus up-regulated Th1 and Tc1 cells, and S. mutans led to increasing levels of their antibodies, which was associated with the induction of Th2 cells. These results may contribute to a better understanding of human lymphocyte interactions to biofilm bacteria, along with their impact on dental and mucosal inflammatory diseases, as well as endocarditis.

Streptococcus gordonii utilizes several distinct gene functions to recruit Porphyromonas gingivalis into a mixed community

Dental plaque biofilm formation proceeds through a developmental pathway initiated by the attachment of pioneer organisms, such as Streptococcus gordonii, to tooth surfaces. Through a variety of synergistic interactions, pioneer organisms facilitate the colonization of later arrivals including Porphyromonas gingivalis, a potential periodontal pathogen. We have investigated genes of S. gordonii required to support a heterotypic biofilm community with P. gingivalis. By screening a plasmid integration library of S. gordonii, genes were identified that are crucial for the accumulation of planktonic P. gingivalis cells into a multispecies biofilm. These genes were further investigated by specific mutation and complementation analyses. The biofilm-associated genes can be grouped into broad categories based on putative function as follows: (i) intercellular or intracellular signalling (cbe and spxB), (ii) cell wall integrity and maintenance of adhesive proteins (murE, msrA and atf), (iii) extracellular capsule biosynthesis (pgsA and atf), and (iv) physiology (gdhA, ccmA and ntpB). In addition, a gene for a hypothetical protein was identified. Biofilm visualization and quantification by confocal microscopy confirmed the role of these genes in the maturation of the multispecies community, including biofilm architectural development. The results suggest that S. gordonii governs the development of heterotypic oral biofilms through multiple genetic pathways.

Binding of the streptococcal surface glycoproteins GspB and Hsa to human salivary proteins

GspB and Hsa are homologous surface glycoproteins of Streptococcus gordonii that bind sialic acid moieties on platelet membrane glycoprotein Ibalpha. Since this species is an important member of the oral flora, we examined the direct binding of these adhesins to human salivary proteins. Both GspB and Hsa bound low-molecular-weight salivary mucin MG2 and salivary agglutinin. Hsa also bound several other salivary proteins, including secretory immunoglobulin A. Screening of six oral streptococcal isolates revealed that at least two of the strains expressed GspB homologues. These results indicate that GspB-like adhesins may be important for oral bacterial colonization.

Structure-function relationships of glucansucrase and fructansucrase enzymes from lactic acid bacteria

Lactic acid bacteria (LAB) employ sucrase-type enzymes to convert sucrose into homopolysaccharides consisting of either glucosyl units (glucans) or fructosyl units (fructans). The enzymes involved are labeled glucansucrases (GS) and fructansucrases (FS), respectively. The available molecular, biochemical, and structural information on sucrase genes and enzymes from various LAB and their fructan and alpha-glucan products is reviewed. The GS and FS enzymes are both glycoside hydrolase enzymes that act on the same substrate (sucrose) and catalyze (retaining) transglycosylation reactions that result in polysaccharide formation, but they possess completely different protein structures. GS enzymes (family GH70) are large multidomain proteins that occur exclusively in LAB. Their catalytic domain displays clear secondary-structure similarity with alpha-amylase enzymes (family GH13), with a predicted permuted (beta/alpha)(8) barrel structure for which detailed structural and mechanistic information is available. Emphasis now is on identification of residues and regions important for GS enzyme activity and product specificity (synthesis of alpha-glucans differing in glycosidic linkage type, degree and type of branching, glucan molecular mass, and solubility). FS enzymes (family GH68) occur in both gram-negative and gram-positive bacteria and synthesize beta-fructan polymers with either beta-(2-->6) (inulin) or beta-(2-->1) (levan) glycosidic bonds. Recently, the first high-resolution three-dimensional structures have become available for FS (levansucrase) proteins, revealing a rare five-bladed beta-propeller structure with a deep, negatively charged central pocket. Although these structures have provided detailed mechanistic insights, the structural features in FS enzymes dictating the synthesis of either beta-(2-->6) or beta-(2-->1) linkages, degree and type of branching, and fructan molecular mass remain to be identified.

Streptococci from root canals in teeth with apical periodontitis receiving endodontic treatment

OBJECTIVES

The object of this study was to investigate the diversity among streptococcal species isolated from root canals in conjunction with endodontic therapy and to characterize their production of extracellular proteins.

STUDY DESIGN

Consecutive root canal samples (RCS) taken as bacteriological controls during root canal treatment of teeth with apical periodontitis were analyzed in a total of 100 clinical cases. Bacteria were isolated and classified by selective media and gas liquid chromatography. Streptococcal strains were identified by carbohydrate fermentation, hydrolysis of aesculin/arginine, and production of enzymes. Releases of extracellular proteins by streptococci and Enterococcus spp in fluid culture media were examined with SDS-PAGE and 2-dimension gel electrophoresis (2 DE). Extracellular proteins produced were quantified and qualitatively analyzed. Specific proteins were targeted with Western immunoblot assays. Comparisons were made with type strains.

RESULTS

Of a total of 241 bacterial strains recovered in the first samples submitted, Streptococcus gordonii, S anginosus, and S oralis were the most frequently isolated streptococci. In 49 of 89 resubmitted samples showing bacterial growth, S gordonii and S oralis still predominated among streptococci. Other common bacterial isolates were Enterococcus spp, Lactobacillus paracasei, and Olsenella uli. Quantitative and qualitative differences in extracellular protein production were observed among clinical isolates and laboratory streptococcal strains. In similar conditions for growth, S intermedius, S anginosus, S oralis, and S gordonii were strong producers of extracellular proteins (>3.0 microg/mL), while Enterococcus spp and S mutans were weak. Whole cell protein extracts showed a different profile from that of extracellular proteins. The chaperone protein DnaK was recognized to be produced extracellularly by S gordonii, S oralis, S anginosus, and S parasanguis.

CONCLUSIONS

Being strong producers of extracellular proteins and by virtue of common presence in teeth undergoing endodontic therapy, S gordonii, S anginosus, and S oralis may be of pathogenic significance in posttreatment apical periodontitis.

The immunoreactivity of systemic antibodies to Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis in adult periodontitis

Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis secrete several potent virulence factors and are known to be two of the major periodontal pathogens. In the present case-control study, the systemic immunoreactivity to A. actinomycetemcomitans exotoxins, cytolethal distending toxin (Cdt) and leukotoxin was analyzed in adult subjects with periodontitis and in periodontally healthy controls. Furthermore, systemic immunoreactivity to P. gingivalis was analyzed in these subjects. Reactivity to the A. actinomycetemcomitans toxins was determined in bioassays that quantified neutralizing antibodies, and P. gingivalis antibodies were detected by enzyme-linked immunosorbent assay (ELISA). The results showed a significantly enhanced immunoreactivity to P. gingivalis in the subjects with periodontitis, while the reactivity to A. actinomycetemcomitans leukotoxin showed no significant difference between patients and controls. However, combined immunoreactivity to leukotoxin and Cdt was more prevalent in the subjects with periodontitis than in the controls. In addition, immunoreactivity to leukotoxin correlated to periodontitis in men but not in women. In conclusion, data from the present study indicate that immunoreactivity to P. gingivalis is frequent in adult periodontitis, while the role of A. actinomycetemcomitans seems to be more complex and depends on gender of the infected subject as well as the virulence of the bacteria.

Short fimbriae of Porphyromonas gingivalis and their role in coadhesion with Streptococcus gordonii

Porphyromonas gingivalis, one of the causative agents of adult periodontitis, attaches and forms biofilms on substrata of Streptococcus gordonii. Coadhesion and biofilm development between these organisms requires the interaction of the short fimbriae of P. gingivalis with the SspB streptococcal surface polypeptide. In this study we investigated the structure and binding activities of the short fimbriae of P. gingivalis. Electron microscopy showed that isolated short fimbriae have an average length of 103 nm and exhibit a helical structure with a pitch of ca. 27 nm. Mfa1, the major protein subunit of the short fimbriae, bound to SspB protein, and this reaction was inhibited by purified recombinant Mfa1 and monospecifc anti-Mfa1 serum in a dose-dependent manner. Complementation of a polar Mfa1 mutant with the mfa1 gene restored the coadhesion phenotype of P. gingivalis. Hence, the Mfa1 structural fimbrial subunit does not require accessory proteins for binding to SspB. Furthermore, the interaction of Mfa1 with SspB is necessary for optimal coadhesion between P. gingivalis and S. gordonii.