Microbiology of the early colonization of human enamel and root surfaces in vivo

Partial denture metal framework may harbor potentially pathogenic bacteria

PURPOSE

The aim of this study was to characterize and compare bacterial diversity on the removable partial denture (RPD) framework over time.

MATERIALS AND METHODS

This descriptive pilot study included five women who were rehabilitated with free-end mandibular RPD. The biofilm on T-bar clasps were collected 1 week (t₁) and 4 months (t₂) after the RPD was inserted (t₀). Bacterial 16S rDNA was extracted and PCR amplified. Amplicons were cloned; clones were submitted to cycle sequencing, and sequences were compared with GenBank (98% similarity).

RESULTS

A total of 180 sequences with more than 499 bp were obtained. Two phylogenetic trees with 84 (t₁) and 96 (t₂) clones represented the bacteria biofilm at the RPD. About 93% of the obtained phylotypes fell into 25 known species for t₁ and 17 for t₂, which were grouped in 5 phyla: Firmicutes (t₁=82%; t₂=60%), Actinobacteria (t₁=5%; t₂=10%), Bacteroidetes (t₁=2%; t₂=6%), Proteobacteria (t₁=10%; t₂=15%) and Fusobacteria (t₁=1%; t₂=8%). The libraries also include 3 novel phylotypes for t₁ and 11 for t₂. Library t₂ differs from t₁ (P=.004); t₁ is a subset of the t₂ (P=.052). Periodontal pathogens, such as F. nucleatum, were more prevalent in t₂.

CONCLUSION

The biofilm composition of the RPD metal clasps changed along time after RPD wearing. The RPD framework may act as a reservoir for potentially pathogenic bacteria and the RPD wearers may benefit from regular follow-up visits and strategies on prosthesis-related oral health instructions.

Microbial Diversity in the Early In Vivo-Formed Dental Biofilm

Although the mature dental biofilm composition is well studied, there is very little information on the earliest phase of in vivo tooth colonization. Progress in dental biofilm collection methodologies and techniques of large-scale microbial identification have made new studies in this field of oral biology feasible. The aim of this study was to characterize the temporal changes and diversity of the cultivable and noncultivable microbes in the early dental biofilm. Samples of early dental biofilm were collected from 11 healthy subjects at 0, 2, 4, and 6 h after removal of plaque and pellicle from tooth surfaces. With the semiquantitative Human Oral Microbiome Identification Microarray (HOMIM) technique, which is based on 16S rRNA sequence hybridizations, plaque samples were analyzed with the currently available 407 HOMIM microbial probes. This led to the identification of at least 92 species, with streptococci being the most abundant bacteria across all time points in all subjects. High-frequency detection was also made with Haemophilus parainfluenzae, Gemella haemolysans, Slackia exigua, and Rothia species. Abundance changes over time were noted for Streptococcus anginosus and Streptococcus intermedius (P = 0.02), Streptococcus mitis bv. 2 (P = 0.0002), Streptococcus oralis (P = 0.0002), Streptococcus cluster I (P = 0.003), G. haemolysans (P = 0.0005), and Stenotrophomonas maltophilia (P = 0.02). Among the currently uncultivable microbiota, eight phylotypes were detected in the early stages of biofilm formation, one belonging to the candidate bacterial division TM7, which has attracted attention due to its potential association with periodontal disease.

The Sialic Acid Binding Protein, Hsa, in Streptococcus gordonii DL1 also Mediates Intergeneric Coaggregation with Veillonella Species

Dental biofilm development involves initial colonization of the tooth’s surface by pioneer colonizers, followed by cell-cell coaggregation between the pioneer and later colonizers. Streptococcus gordonii is one of the pioneer colonizers. In addition to its role in oral biofilm development, S. gordonii also is a pathogen in infective endocarditis in susceptible humans. A surface adhesin, Hsa, has been shown to play a critical role in colonization of S. gordonii on the heart tissue; however, its role in oral biofilm development has not been reported. In this study we demonstrate that Hsa is essential for coaggregation between S. gordonii and Veillonella sp., which are bridging species connecting the pioneer colonizers to the late colonizers. Interestingly, the same domains shown to be required for Hsa binding to sialic acid on the human cell surface are also required for coaggregation with Veillonella sp. However, sialic acid appeared not to be required for this intergeneric coaggregation. This result suggests that although the same domains of Hsa are involved in binding to eukaryotic as well as Veillonella cells, the binding mechanism is different. The gene expression pattern of hsa was also studied and shown not to be induced by coaggregation with Veillonella sp.

Identifying essential Streptococcus sanguinis genes using genome-wide deletion mutation

Essential genes in pathogens are important for the development of antibacterial drugs. In this report, we described a protocol to identify essential genes in the Streptococcus sanguinis SK36 strain using genome-wide deletion mutation. A fusion PCR-based method is used to construct gene deletion fragments, which contain kanamycin resistance cassettes with two flanking arms of DNA upstream and downstream of the target gene. The linear fused PCR amplicons were transformed into S. sanguinis SK36 cells. No kanamycin-resistant transformants suggested the gene essentiality because the deletion of the essential gene renders a lethal phenotype of the transformants. The putative essential genes were further confirmed by independent transformations up to five attempts. The false nonessential genes were also identified by removing double-band mutants.

Low-dose irradiation affects the functional behavior of oral microbiota in the context of mucositis

The role of host-microbe interactions in the pathobiology of oral mucositis is still unclear; therefore, this study aimed to unravel the effect of irradiation on behavioral characteristics of oral microbial species in the context of mucositis. Using various experimental in vitro setups, the effects of irradiation on growth and biofilm formation of two Candida spp., Streptococcus salivarius and Klebsiella oxytoca in different culture conditions were evaluated. Irradiation did not affect growth of planktonic cells, but reduced the number of K. oxytoca cells in newly formed biofilms cultured in static conditions. Biofilm formation of K. oxytoca and Candida glabrata was affected by irradiation and depended on the culturing conditions. In the presence of mucins, these effects were lost, indicating the protective nature of mucins. Furthermore, the Galleria melonella model was used to study effects on microbial virulence. Irradiated K. oxytoca microbes were more virulent in G. melonella larvae compared to the nonirradiated ones. Our data indicate that low-dose irradiation can have an impact on functional characteristics of microbial species. Screening for pathogens like K. oxytoca in the context of mucosits could be useful to allow early detection and immediate intervention.

The interaction between Streptococcus spp. and Veillonella tobetsuensis in the early stages of oral biofilm formation

Dental plaque is a multispecies oral biofilm, the development of which is initiated by adherence of the pioneer Streptococcus spp. Oral Veillonella spp., including V. atypica, V. denticariosi, V. dispar, V. parvula, V. rogosae, and V. tobetsuensis, are known as early colonizers in oral biofilm formation. These species have been reported to co-aggregate with Streptococcus spp. in a metabolic cooperation-dependent manner to form biofilms in human oral cavities, especially in the early stages of biofilm formation. However, in our previous study, Streptococcus gordonii showed biofilm formation to the greatest extent in the presence of V. tobetsuensis, without co-aggregation between species. These results suggest that V. tobetsuensis produces signaling molecules that promote the proliferation of S. gordonii in biofilm formation. It is well known in many bacterial species that the quorum-sensing (QS) system regulates diverse functions such as biofilm formation. However, little is known about the QS system with autoinducers (AIs), between Veillonella and Streptococcus. Recently, AI-1 and AI-2 were detected and identified in the culture supernatants of V. tobetsuensis as strong signaling molecules in biofilm formation with S. gordonii. In particular, the supernatant from V. tobetsuensis showed the highest AI-2 activity among 6 oral Veillonella species, indicating that AIs, mainly AI-2, produced by V. tobetsuensis may be important factors and may facilitate biofilm formation of S. gordonii. Clarifying the mechanism that underlies the QS system between S. gordonii and V. tobetsuensis may lead to the development of novel methods for the prevention of oral infectious diseases caused by oral biofilms.

Effect of fluoride and chlorhexidine digluconate mouthrinses on plaque biofilms

Objective : To develop a model in which to investigate the architecture of plaque biofilms formed on enamel surfaces in vivo and to compare the effects of anti-microbial agents of relevance for caries on biofilm vitality. Materials and Methodology : Enamel discs mounted on healing abutments in the pre-molar region were worn by three subjects for 7 days. Control discs were removed before subjects rinsed with 0.1% chlorhexidine digluconate (CHX) or 0.2% sodium fluoride (NaF) for 1 minute. Biofilms were stained with Baclight Live/Dead and z-stacks of images created using confocal scanning laser micoscopy. The levels of vital and dead/damaged bacteria in the biofilms, assessed as the proportion of green and red pixels respectively, were analysed using ImageTrak^® software. Results : The subjects showed individual differences in biofilm architecture. The thickness of the biofilms varied from 28-96µm although cell density was always the greatest in the middle layers. In control biofilms, the overall levels of vitality were high (71-98%) especially in the area closest to the enamel interface. Rinsing with either CHX or NaF caused a similar reduction in overall vitality. CHX exerted an effect throughout the biofilm, particularly on the surface of cell clusters whereas NaF caused cell damage/death mainly in the middle to lower biofilm layers. Conclusion : We describe a model that allows the formation of mature, undisturbed oral biofilms on human enamel surfaces in vivo and show that CHX and NaF have a similar effect on overall vitality but differ in their sites of action.

Proteome analysis identifies the Dpr protein of Streptococcus mutans as an important factor in the presence of early streptococcal colonizers of tooth surfaces

Oral streptococci are primary colonizers of tooth surfaces and Streptococcus mutans is the principal causative agent of dental caries in humans. A number of proteins are involved in the formation of monospecies biofilms by S. mutans. This study analyzed the protein expression profiles of S. mutans biofilms formed in the presence or absence of S. gordonii, a pioneer colonizer of the tooth surface, by two-dimensional gel electrophoresis (2-DE). After identifying S. mutans proteins by Mass spectrometric analysis, their expression in the presence of S. gordonii was analyzed. S. mutans was inoculated with or without S. gordonii DL1. The two species were compartmentalized using 0.2-μl Anopore membranes. The biofilms on polystyrene plates were harvested, and the solubilized proteins were separated by 2-DE. When S. mutans biofilms were formed in the presence of S. gordonii, the peroxide resistance protein Dpr of the former showed 4.3-fold increased expression compared to biofilms that developed in the absence of the pioneer colonizer. In addition, we performed a competition assay using S. mutans antioxidant protein mutants together with S. gordonii and other initial colonizers. Growth of the dpr-knockout S. mutans mutant was significantly inhibited by S. gordonii, as well as by S. sanguinis. Furthermore, a cell viability assay revealed that the viability of the dpr-defective mutant was significantly attenuated compared to the wild-type strain when co-cultured with S. gordonii. Therefore, these results suggest that Dpr might be one of the essential proteins for S. mutans survival on teeth in the presence of early colonizing oral streptococci.

A YadA-like autotransporter, Hag1 in Veillonella atypica is a multivalent hemagglutinin involved in adherence to oral streptococci, Porphyromonas gingivalis, and human oral buccal cells

Dental biofilm development is a sequential process, and adherence between microbes and the salivary pellicle (adhesion) as well as among different microbes (co-adhesion or coaggregation) plays a critical role in building a biofilm community. The Veillonella species are among the most predominant species in the oral cavity and coaggregate with many initial, early, middle, and late colonizers. Similar to oral fusobacteria, they are also considered bridging species in biofilm development. However, the mechanism of this ability has yet to be reported, due to the previous lack of a genetic transformation system in the entire genus. In this study, we used our recently discovered transformable Veillonella strain, Veillonella atypica OK5, to probe the mechanism of coaggregation between Veillonella species and other oral bacteria. By insertional inactivation of all eight putative hemagglutinin genes, we identified one gene, hag1, which is involved in V. atypica coaggregation with the initial colonizers Streptococcus gordonii, Streptococcus oralis and Streptococcus cristatus, and the periodontal pathogen Porphyromonas gingivalis. The hag1 mutant also abolished adherence to human buccal cells. Inhibition assays using various chemical or physiological treatments suggest different mechanisms being involved in coaggregation with different partners. The entire hag1 gene was sequenced and shown to be the largest known bacterial hemagglutinin gene.

Identification and analysis of potential targets in Streptococcus sanguinis using computer aided protein data analysis

PURPOSE

Streptococcus sanguinis is a Gram-positive, facultative aerobic bacterium that is a member of the viridans streptococcus group. It is found in human mouths in dental plaque, which accounts for both dental cavities and bacterial endocarditis, and which entails a mortality rate of 25%. Although a range of remedial mediators have been found to control this organism, the effectiveness of agents such as penicillin, amoxicillin, trimethoprim-sulfamethoxazole, and erythromycin, was observed. The emphasis of this investigation was on finding substitute and efficient remedial approaches for the total destruction of this bacterium.

MATERIALS AND METHODS

In this computational study, various databases and online software were used to ascertain some specific targets of S. sanguinis. Particularly, the Kyoto Encyclopedia of Genes and Genomes databases were applied to determine human nonhomologous proteins, as well as the metabolic pathways involved with those proteins. Different software such as Phyre2, CastP, DoGSiteScorer, the Protein Function Predictor server, and STRING were utilized to evaluate the probable active drug binding site with its known function and protein-protein interaction.

RESULTS

In this study, among 218 essential proteins of this pathogenic bacterium, 81 nonhomologous proteins were accrued, and 15 proteins that are unique in several metabolic pathways of S. sanguinis were isolated through metabolic pathway analysis. Furthermore, four essentially membrane-bound unique proteins that are involved in distinct metabolic pathways were revealed by this research. Active sites and druggable pockets of these selected proteins were investigated with bioinformatic techniques. In addition, this study also mentions the activity of those proteins, as well as their interactions with the other proteins.

CONCLUSION

Our findings helped to identify the type of protein to be considered as an efficient drug target. This study will pave the way for researchers to develop and discover more effective and specific therapeutic agents against S. sanguinis.

Proteins, pathogens, and failure at the composite-tooth interface

In the United States, composites accounted for nearly 70% of the 173.2 million composite and amalgam restorations placed in 2006 (Kingman et al., 2012), and it is likely that the use of composite will continue to increase as dentists phase out dental amalgam. This trend is not, however, without consequences. The failure rate of composite restorations is double that of amalgam (Ferracane, 2013). Composite restorations accumulate more biofilm, experience more secondary decay, and require more frequent replacement. In vivo biodegradation of the adhesive bond at the composite-tooth interface is a major contributor to the cascade of events leading to restoration failure. Binding by proteins, particularly gp340, from the salivary pellicle leads to biofilm attachment, which accelerates degradation of the interfacial bond and demineralization of the tooth by recruiting the pioneer bacterium Streptococcus mutans to the surface. Bacterial production of lactic acid lowers the pH of the oral microenvironment, erodes hydroxyapatite in enamel and dentin, and promotes hydrolysis of the adhesive. Secreted esterases further hydrolyze the adhesive polymer, exposing the soft underlying collagenous dentinal matrix and allowing further infiltration by the pathogenic biofilm. Manifold approaches are being pursued to increase the longevity of composite dental restorations based on the major contributing factors responsible for degradation. The key material and biological components and the interactions involved in the destructive processes, including recent advances in understanding the structural and molecular basis of biofilm recruitment, are described in this review. Innovative strategies to mitigate these pathogenic effects and slow deterioration are discussed.

Proteomics of Fusobacterium nucleatum within a model developing oral microbial community

Fusobacterium nucleatum is a common oral organism that can provide adhesive and metabolic support to developing periodontal bacterial communities. It is within the context of these communities that disease occurs. We have previously reported whole cell proteomics analyses of Porphyromonas gingivalis and Streptococcus gordonii in early-stage communities with each other and with F. nucleatum, modeled using 18 h pellets. Here, we report the adaptation of F. nucleatum to the same experimental conditions as measured by differential protein expression. About 1210 F. nucleatum proteins were detected in single species F. nucleatum control samples, 1192 in communities with P. gingivalis, 1224 with S. gordonii, and 1135 with all three species. Quantitative comparisons among the proteomes revealed important changes in all mixed samples with distinct responses to P. gingivalis or S. gordonii alone and in combination. The results were inspected manually and an ontology analysis conducted using DAVID (Database for annotation, visualization, and integrated discovery). Extensive changes were detected in energy metabolism. All multispecies comparisons showed reductions in amino acid fermentation and a shift toward butanoate as a metabolic byproduct, although the two organism model community with S. gordonii showed increases in alanine, threonine, methionine, and cysteine pathways, and in the three species samples there were increases in lysine and methionine. The communities with P. gingivalis or all three organisms showed reduced glycolysis proteins, but F. nucleatum paired with S. gordonii displayed increased glycolysis/gluconeogenesis proteins. The S. gordonii containing two organism model also showed increases in the ethanolamine pathway while the three species sample showed decreases relative to the F. nucleatum single organism control. All of the nascent model communities displayed reduced translation, lipopolysaccharide, and cell wall biosynthesis, DNA replication and DNA repair.

Adherence of human oral keratinocytes and gingival fibroblasts to nano-structured titanium surfaces

Background

A key element for long-term success of dental implants is integration of the implant surface with the surrounding host tissues. Modification of titanium implant surfaces can enhance osteoblast activity but their effects on soft-tissue cells are unclear. Adherence of human keratinocytes and gingival fibroblasts to control commercially pure titanium (CpTi) and two surfaces prepared by anodic oxidation was therefore investigated. Since implant abutments are exposed to a bacteria-rich environment in vivo, the effect of oral bacteria on keratinocyte adhesion was also evaluated.

Methods

The surfaces were characterized using scanning electron microscopy (SEM). The number of adhered cells and binding strength, as well as vitality of fibroblasts and keratinocytes were evaluated using confocal scanning laser microscopy after staining with Live/Dead Baclight. To evaluate the effect of bacteria on adherence and vitality, keratinocytes were co-cultured with a four-species streptococcal consortium.

Results

SEM analysis showed the two anodically oxidized surfaces to be nano-structured with differing degrees of pore-density. Over 24 hours, both fibroblasts and keratinocytes adhered well to the nano-structured surfaces, although to a somewhat lesser degree than to CpTi (range 42-89% of the levels on CpTi). The strength of keratinocyte adhesion was greater than that of the fibroblasts but no differences in adhesion strength could be observed between the two nano-structured surfaces and the CpTi. The consortium of commensal streptococci markedly reduced keratinocyte adherence on all the surfaces as well as compromising membrane integrity of the adhered cells.

Conclusion

Both the vitality and level of adherence of soft-tissue cells to the nano-structured surfaces was similar to that on CpTi. Co-culture with streptococci reduced the number of keratinocytes on all the surfaces to approximately the same level and caused cell damage, suggesting that commensal bacteria could affect adherence of soft-tissue cells to abutment surfaces in vivo.

Application of metagenomics in understanding oral health and disease

Oral diseases including periodontal disease and caries are some of the most prevalent infectious diseases in humans. Different microbial species cohabitate and form a polymicrobial biofilm called dental plaque in the oral cavity. Metagenomics using next generation sequencing technologies has produced bacterial profiles and genomic profiles to study the relationships between microbial diversity, genetic variation, and oral diseases. Several oral metagenomic studies have examined the oral microbiome of periodontal disease and caries. Gene annotations in these studies support the association of specific genes or metabolic pathways with oral health and with specific diseases. The roles of pathogenic species and functions of specific genes in oral disease development have been recognized by metagenomic analysis. A model is proposed in which three levels of interactions occur in the oral microbiome that determines oral health or disease.

The impact of dairy consumption on salivary inoculum

Quantitative levels of harmful oral microbes present following complex surgical excisions of head and neck cancer are important since wounds are often contaminated through direct connection to the oral cavity and its flora. This possibility is especially important in irradiated patients who have decreased protective salivary function. In addition, high oral microbial levels increase and intensify oral mucositis leading to significant morbidity in patients treated with radiation therapy. One previously untested surgical teaching to decrease the bacterial inoculum present in the oral cavity is to counsel patients against consuming otherwise nutritious dairy products, as they are thought to coat the oral cavity with rate-limiting nutrients vital for bacterial growth. This risk may extend to individuals with chronic laryngeal penetration or aspiration, since salivary bacterial load might represent a lethal threat in the presence of marginal pulmonary reserve. A crossover study using six healthy adult volunteers and six patients who had previously undergone radiation therapy to an oropharyngeal primary site was performed. Saliva samples were quantitatively cultured in both groups with and without the consumption of dairy products at 1-h and 5-h intervals. Analysis of quantitative cultures demonstrated that the consumption of dairy products had no influence on bacterial levels present in previously radiated subjects and nonirradiated controls. Additionally, the consumption of dairy did not affect the composition of microbes present. Due to the lack of changes in both quantity and composition of oral bacteria seen in this study, patients would not benefit from the avoidance of dairy products.

Mass Spectrometric Analysis of Whole Secretome and Amylase-precipitated Secretome Proteins from Streptococcus gordonii

Oral biofilm (dental plaque) is formed by the initial adhesion of “pioneer species” to salivary proteins that form the dental pellicle on the tooth surface. One such pioneer species, Streptococcus gordonii, is known to bind salivary amylase through specific amylase-binding proteins such as amylase-binding protein A (AbpA). Recent studies have demonstrated that once bound, salivary amylase appears to modulate gene expression in S. gordonii. However, it is not known if this amylase-induced gene expression leads to secretion of proteins that play a role in plaque biofilm formation. In this study we examined the differences in secreted proteomes between S. gordonii KS1 (wild type) and AbpA-deficient (ΔAbpA) strains. We also examined the differentially precipitated secretome proteins following incubation with salivary amylase. The culture supernatants from KS1 and ΔAbpA were analyzed by nano-LC/MS/MS to characterize the whole secreted proteomes of the KS1 and ΔAbpA. A total of 107 proteins were identified in the KS1 and ΔAbpA secretomes of which 72 proteins were predicted to have an N-terminal signal peptide for secretion. Five proteins were differentially expressed between the KS1 and ΔAbpA secretomes; AbpA and sortase B were expressed exclusively by KS1, whereas Gdh, AdcA and GroEL were expressed only by ΔAbpA. Incubation of culture supernatants from KS1 and ΔAbpA with amylase (50 μg/ml) at room temperature for 2 h resulted in the differential precipitation of secretome proteins. Hypothetical protein (SGO_0483), cation-transporting ATPase YfgQ (Aha1), isocitrate dehydrogenase (Icd), sortase A (SrtA), beta-N-acetylhexosaminidase (SGO_0405), peptide chain release factor 1(PrfA) and cardiolipin synthase (SGO_2037) were precipitated by amylase from the KS1 culture supernatant. Among the identified secreted proteins and amylase-precipitated proteins, transcriptional regulator LytR (SGO_0535) and cation-transporting ATPase YfgQ (Aha1) are potential signaling proteins.

Salivary pellicles on titanium and their effect on metabolic activity in Streptococcus oralis

BACKGROUND

Titanium implants in the oral cavity are covered with a saliva-derived pellicle to which early colonizing microorganisms such as Streptococcus oralis can bind. The protein profiles of salivary pellicles on titanium have not been well characterized and the proteins of importance for binding are thus unknown. Biofilm bacteria exhibit different phenotypes from their planktonic counterparts and contact with salivary proteins may be one factor contributing to the induction of changes in physiology. We have characterized salivary pellicles from titanium surfaces and investigated how contact with uncoated and saliva-coated titanium surfaces affects metabolic activity in adherent cells of S. oralis.

METHODS

Salivary pellicles on smooth titanium surfaces were desorbed and these, as well as purified human saliva, were subjected to two-dimensional gel electrophoresis and mass spectroscopy. A parallel plate flow-cell model was used to study binding of a fresh isolate of S. oralis to uncoated and saliva-coated titanium surfaces. Metabolic activity was assessed using the BacLight CTC Vitality Kit and confocal scanning laser microscopy. Experiments were carried out in triplicate and the results analyzed using Student's t-test or ANOVA.

RESULTS

Secretory IgA, α-amylase and cystatins were identified as dominant proteins in the salivary pellicles. Selective adsorption of proteins was demonstrated by the enrichment of prolactin-inducible protein and absence of zinc-α₂-glycoprotein relative to saliva. Adherence of S. oralis to titanium led to an up-regulation of metabolic activity in the population after 2 hours. In the presence of a salivary pellicle, this effect was enhanced and sustained over the following 22 hour period.

CONCLUSIONS

We have shown that adherence to smooth titanium surfaces under flow causes an up-regulation of metabolic activity in the early oral colonizer S. oralis, most likely as part of an adaptation to the biofilm mode of life. The effect was enhanced by a salivary pellicle containing sIgA, α-amylase, cystatins and prolactin-inducible protein which was, for the first time, identified as an abundant component of salivary pellicles on titanium. Further studies are needed to clarify the mechanisms underlying the effect of surface contact on metabolic activity as well as to identify the salivary proteins responsible for enhancing the effect.

Mechanistic model of Rothia mucilaginosa adaptation toward persistence in the CF lung, based on a genome reconstructed from metagenomic data

The impaired mucociliary clearance in individuals with Cystic Fibrosis (CF) enables opportunistic pathogens to colonize CF lungs. Here we show that Rothia mucilaginosa is a common CF opportunist that was present in 83% of our patient cohort, almost as prevalent as Pseudomonas aeruginosa (89%). Sequencing of lung microbial metagenomes identified unique R. mucilaginosa strains in each patient, presumably due to evolution within the lung. The de novo assembly of a near-complete R. mucilaginosa (CF1E) genome illuminated a number of potential physiological adaptations to the CF lung, including antibiotic resistance, utilization of extracellular lactate, and modification of the type I restriction-modification system. Metabolic characteristics predicted from the metagenomes suggested R. mucilaginosa have adapted to live within the microaerophilic surface of the mucus layer in CF lungs. The results also highlight the remarkable evolutionary and ecological similarities of many CF pathogens; further examination of these similarities has the potential to guide patient care and treatment.

Wound biofilms: lessons learned from oral biofilms

Biofilms play an important role in the development and pathogenesis of many chronic infections. Oral biofilms, more commonly known as dental plaque, are a primary cause of oral diseases including caries, gingivitis, and periodontitis. Oral biofilms are commonly studied as model biofilm systems as they are easily accessible; thus, biofilm research in oral diseases is advanced with details of biofilm formation and bacterial interactions being well elucidated. In contrast, wound research has relatively recently directed attention to the role biofilms have in chronic wounds. This review discusses the biofilms in periodontal disease and chronic wounds with comparisons focusing on biofilm detection, biofilm formation, the immune response to biofilms, bacterial interaction, and quorum sensing. Current treatment modalities used by both fields and future therapies are also discussed.

Microbial analysis of bite marks by sequence comparison of streptococcal DNA

Bite mark injuries often feature in violent crimes. Conventional morphometric methods for the forensic analysis of bite marks involve elements of subjective interpretation that threaten the credibility of this field. Human DNA recovered from bite marks has the highest evidentiary value, however recovery can be compromised by salivary components. This study assessed the feasibility of matching bacterial DNA sequences amplified from experimental bite marks to those obtained from the teeth responsible, with the aim of evaluating the capability of three genomic regions of streptococcal DNA to discriminate between participant samples. Bite mark and teeth swabs were collected from 16 participants. Bacterial DNA was extracted to provide the template for PCR primers specific for streptococcal 16S ribosomal RNA (16S rRNA) gene, 16S–23S intergenic spacer (ITS) and RNA polymerase beta subunit (rpoB). High throughput sequencing (GS FLX 454), followed by stringent quality filtering, generated reads from bite marks for comparison to those generated from teeth samples. For all three regions, the greatest overlaps of identical reads were between bite mark samples and the corresponding teeth samples. The average proportions of reads identical between bite mark and corresponding teeth samples were 0.31, 0.41 and 0.31, and for non-corresponding samples were 0.11, 0.20 and 0.016, for 16S rRNA, ITS and rpoB, respectively. The probabilities of correctly distinguishing matching and non-matching teeth samples were 0.92 for ITS, 0.99 for 16S rRNA and 1.0 for rpoB. These findings strongly support the tenet that bacterial DNA amplified from bite marks and teeth can provide corroborating information in the identification of assailants.

Taking the starch out of oral biofilm formation: molecular basis and functional significance of salivary α-amylase binding to oral streptococci

α-Amylase-binding streptococci (ABS) are a heterogeneous group of commensal oral bacterial species that comprise a significant proportion of dental plaque microfloras. Salivary α-amylase, one of the most abundant proteins in human saliva, binds to the surface of these bacteria via specific surface-exposed α-amylase-binding proteins. The functional significance of α-amylase-binding proteins in oral colonization by streptococci is important for understanding how salivary components influence oral biofilm formation by these important dental plaque species. This review summarizes the results of an extensive series of studies that have sought to define the molecular basis for α-amylase binding to the surface of the bacterium as well as the biological significance of this phenomenon in dental plaque biofilm formation.

Microscope-based imaging platform for large-scale analysis of oral biofilms

A microscopic method for noninvasively monitoring oral biofilms at the macroscale was developed to describe the spatial distribution of biofilms of different bacterial composition on bovine enamel surfaces (BES). For this purpose, oral biofilm was grown in situ on BES that were fixed at approximal sites of individual upper jaw acrylic devices worn by a volunteer for 3 or 5 days. Eubacteria, Streptococcus spp., and Fusobacterium nucleatum were stained using specific fluorescence in situ hybridization (FISH) probes. The resulting fluorescence signals were subsequently tested by confocal laser scanning microscopy (CLSM) and monitored by an automated wide-field microscope-based imaging platform (Scan∧R). Automated image processing and data analysis were conducted by microscope-associated software and followed by statistical evaluation of the results. The full segmentation of biofilm images revealed a random distribution of bacteria across the entire area of the enamel surfaces examined. Significant differences in the composition of the microflora were recorded across individual as well as between different enamel surfaces varying from sparsely colonized (47.26%) after 3 days to almost full surface coverage (84.45%) after 5 days. The enamel plates that were positioned at the back or in the middle of the oral cavity were found to be more suitable for the examination of biofilms up to 3 days old. In conclusion, automated microscopy combined with the use of FISH can enable the efficient visualization and meaningful quantification of bacterial composition over the entire sample surface. Due to the possibility of automation, Scan∧R overcomes the technical limitations of conventional CLSM.

Proteomics of Streptococcus gordonii within a model developing oral microbial community

Background

Streptococcus gordonii is one of several species that can initiate the formation of oral biofilms that develop into the complex multispecies microbial communities referred to as dental plaque. It is in the context of dental plaque that periodontal pathogens such as Porphyromonas gingivalis cause disease. We have previously reported a whole cell quantitative proteomics investigation of P. gingivalis in a model dental plaque community of S. gordonii, P. gingivalis, and Fusobacterium nucleatum. Here we report the adaptation of S. gordonii to the same model.

Results

1122 S. gordonii proteins were detected in S. gordonii control samples, 915 in communities with F. nucleatum, 849 with P. gingivalis, and 649 with all three organisms. Quantitative comparisons showed extensive proteome changes in association with F. nucleatum or P. gingivalis individually or both P. gingivalis and F. nucleatum together. The changes were species specific, though the P. gingivalis interaction may be dominant, indicated by large differences between the proteomes with F. nucleatum or P. gingivalis but limited changes between communities with P. gingivalis or both P. gingivalis and F. nucleatum. The results were inspected manually and an ontology analysis conducted using DAVID. Extensive changes were seen in nutrition pathways with increases in energy metabolism and changes in the resulting byproducts, while the acid and sugar repressed PTS (phosphoenolpyruvate dependent phosphotransferase system) sugar transport systems showed decreases. These results were seen across all the multispecies samples, though with different profiles according to the partner species. F. nucleatum association decreased proteins for the metabolic end products acetate and ethanol but increased lactate, the primary source of acidity from streptococcal cultures. P. gingivalis containing samples had a reduction in levels of proteins for ethanol and formate but increased proteins for both acetate and lactate production. The communities also showed increases in exopolysaccharide synthesis, amino acid biosynthesis, and oxidative stress protection and decreases in adhesion and transporter proteins.

Conclusion

This study showed that S. gordonii demonstrates species specific responses during interactions with F. nucleatum or P. gingivalis. Extensive changes were seen in energy metabolism and byproduct production implicating nutrient transfer as an important community interaction.

Pathogenicity of exopolysaccharide-producing Actinomyces oris isolated from an apical abscess lesion

Aim

To demonstrate a capacity for producing exopolysaccharides (EPSs) and an ability to form biofilm on abiotic materials of Actinomyces oris strain K20.

Methodology

The productivity of EPSs and the ability to form biofilm of strain K20 were evaluated by measuring viscosity of spent culture media and by scanning electron microscopy (SEM) and the biofilm assay on microtitre plates, respectively. High-performance liquid chromatography was used to determine the chemical composition of the viscous materials. To examine the role of the viscous materials attributable to the pathogenicity in this organism, the ability of strain K20 to induce abscess formation was compared in mice to that of ATCC 27044.

Results

The viscosity of the spent culture media of K20 was significantly higher than that of ATCC 27044. Strain K20 showed dense meshwork structures around the cells and formed biofilms on microtitre plates, whereas ATCC 27044 did not. Chemical analysis of the viscous materials revealed that they were mainly composed of neutral sugars with mannose constituting 77.5% of the polysaccharides. Strain K20 induced persistent abscesses in mice lasting at least 5 days at a concentration of 10⁸ cells mL⁻¹, whereas abscesses induced by ATCC 27044 healed and disappeared or decreased in size at day 5.

Conclusions

Strain K20 produced EPSs, mainly consisting of mannose, and formed biofilms. This phenotype might play an important role for A. oris to express virulence through the progression of apical periodontitis.

Photodynamic inactivation of Streptococcus mutans and Streptococcus sanguinis biofilms in vitro

The purpose of this study was to evaluate specific effects of photodynamic inactivation (PDI) using erythrosine (ER) and Rose Bengal (RB) photosensitizers and a blue light-emitting diode (LED) on the viability of Streptococcus mutans and Streptococcus sanguinis biofilms. Biofilms were grown in acrylic disks immersed in broth to production of biofilms, inoculated with microbial suspension (10(6) cells/mL) and incubated for 48 h. After the formation of biofilms, the effects of the photosensitizers ER and RB at a concentration of 5 μM for 5 min and blue LED (455 ± 20 nm) for 180 s, photosensitizers alone and conjugated were evaluated. Next, the disks were placed in tubes with sterile physiological solution (0.9 % sodium chloride) and sonicated for to disperse the biofilms. Tenfold serial dilutions were carried and aliquots seeded in brain heart infusion agar which were then incubated for 48 h. Then the numbers colony-forming units per milliliter (CFU/mL; log10) were counted and analyzed statistically (ANOVA, Tukey test, P ≤ 0.05). Significant decreases in the viability of all microorganisms were observed for biofilms exposed to PDI mediated by both photosensitizers. The reductions with RB and ER were, 0.62 and 0.52 log10 CFU mL(-1) for S. mutans biofilms (p=0.001), and 0.95 and 0.88 log10 CFU mL(-1) for S. sanguinis biofilms (p=0.001), respectively. The results showed that biofilms formed in vitro by S. mutans and S. sanguinis, were sensitive to PDI using a blue LED associated with photosensitizers ER or RB, indicating its use in the control of caries and periodontal diseases.

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.

Autoinducer-2 influences interactions amongst pioneer colonizing streptococci in oral biofilms

Streptococcus gordonii and Streptococcus oralis are among the first bacterial species to colonize clean tooth surfaces. Both produce autoinducer-2 (AI-2): a family of inter-convertible cell-cell signal molecules synthesized by the LuxS enzyme. The overall aim of this work was to determine whether AI-2 alters interspecies interactions between S. gordonii DL1 and S. oralis 34 within dual-species biofilms in flowing human saliva. Based upon AI-2 bioluminescence assays, S. gordonii DL1 produced more AI-2 activity than S. oralis 34 in batch culture, and both were able to remove AI-2 activity from solution. In single-species, saliva-fed flowcell systems, S. oralis 34 formed scant biofilms that were similar to the luxS mutant. Conversely, S. gordonii DL1 formed confluent biofilms while the luxS mutant formed architecturally distinct biofilms that possessed twofold greater biovolume than the wild-type. Supplementing saliva with 0.1-10 nM chemically synthesized AI-2 (csAI-2) restored the S. gordonii DL1 luxS biofilm phenotype to that which was similar to the wild-type; above or below this concentration range, biofilms were architecturally similar to that formed by the luxS mutant. In dual-species biofilms, S. gordonii DL1 was always more abundant than S. oralis 34. Compared with dual-species, wild-type biofilms, the biovolume occupied by S. oralis 34 was reduced by greater than sevenfold when neither species produced AI-2. The addition of 1 nM csAI-2 to the dual-species luxS-luxS mutant biofilms re-established the biofilm phenotype to resemble that of the wild-type pair. Thus, this work demonstrates that AI-2 can alter the biofilm structure and composition of pioneering oral streptococcal biofilms. This may influence the subsequent succession of other species into oral biofilms and the ecology of dental plaque.

Streptococcus cristatus ArcA interferes with Porphyromonas gingivalis pathogenicity in mice

BACKGROUND AND OBJECTIVE

Porphyromonas gingivalis has been implicated as one of the major pathogens in chronic periodontitis, an infectious disease affecting the majority of the adult population. We have previously demonstrated that a surface protein, arginine deiminase (ArcA), of Streptococcus cristatus represses production of P. gingivalis long fimbriae and interrupts the formation of P. gingivalis biofilms in vitro. Our in vivo studies have also shown that the distribution of P. gingivalis and S. cristatus in human subgingival plaque is negatively correlated. The objective of this study was to determine if S. cristatus ArcA inhibits P. gingivalis colonization and attenuates its subsequent pathogenesis in alveolar bone loss in the murine oral cavity.

MATERIAL AND METHODS

A wild-type strain of S. cristatus (CC5A) and its arcA knockout mutant (ArcAE) were used as initial colonizers in the oral cavity of BALB/cByJ mice. Colonization of P. gingivalis on the existing S. cristatus biofilms was assessed by quantitative PCR, and P. gingivalis-induced alveolar bone loss was measured 6 wk after P. gingivalis infection.

RESULTS

The presence of S. cristatus CC5A, but not its arcA mutant, attenuated P. gingivalis colonization in the murine oral cavity. In addition, P. gingivalis-induced alveolar bone loss was significantly lower in mice initially infected with S. cristatus CC5A than in those infected with the arcA mutant.

CONCLUSION

This study provides direct evidence that S. cristatus ArcA has an inhibitory effect on P. gingivalis colonization, which may in turn attenuate the pathogenicity of P. gingivalis.

Acetyl-11-keto-β-boswellic acid (AKBA); targeting oral cavity pathogens

BACKGROUND

Boswellic acids mixture of triterpenic acids obtained from the oleo gum resin of Boswellia serrata and known for its effectiveness in the treatment of chronic inflammatory disease including peritumor edema. Boswellic acids have been extensively studied for a number of activities including anti inflammatory, antitumor, immunomodulatory, and inflammatory bowel diseases. The present study describes the antimicrobial activities of boswellic acid molecules against oral cavity pathogens. Acetyl-11-keto-β-boswellic acid (AKBA), which exhibited the most potent antibacterial activity, was further evaluated in time kill studies, mutation prevention frequency, postantibiotic effect (PAE) and biofilm susceptibility assay against oral cavity pathogens.

FINDINGS

AKBA exhibited an inhibitory effect on all the oral cavity pathogens tested (MIC of 2-4 μg/ml). It exhibited concentration dependent killing of Streptococcus mutans ATCC 25175 up to 8 × MIC and also prevented the emergence of mutants of S.mutans ATCC 25175 at 8× MIC. AKBA demonstrated postantibiotic effect (PAE) of 5.7 ± 0.1 h at 2 × MIC. Furthermore, AKBA inhibited the formation of biofilms generated by S.mutans and Actinomyces viscosus and also reduced the preformed biofilms by these bacteria.

CONCLUSIONS

AKBA can be useful compound for the development of antibacterial agent against oral pathogens and it has great potential for use in mouthwash for preventing and treating oral infections.

pH landscapes in a novel five-species model of early dental biofilm

BACKGROUND

Despite continued preventive efforts, dental caries remains the most common disease of man. Organic acids produced by microorganisms in dental plaque play a crucial role for the development of carious lesions. During early stages of the pathogenetic process, repeated pH drops induce changes in microbial composition and favour the establishment of an increasingly acidogenic and aciduric microflora. The complex structure of dental biofilms, allowing for a multitude of different ecological environments in close proximity, remains largely unexplored. In this study, we designed a laboratory biofilm model that mimics the bacterial community present during early acidogenic stages of the caries process. We then performed a time-resolved microscopic analysis of the extracellular pH landscape at the interface between bacterial biofilm and underlying substrate.

METHODOLOGY/PRINCIPAL FINDINGS

Strains of Streptococcus oralis, Streptococcus sanguinis, Streptococcus mitis, Streptococcus downei and Actinomyces naeslundii were employed in the model. Biofilms were grown in flow channels that allowed for direct microscopic analysis of the biofilms in situ. The architecture and composition of the biofilms were analysed using fluorescence in situ hybridization and confocal laser scanning microscopy. Both biofilm structure and composition were highly reproducible and showed similarity to in-vivo-grown dental plaque. We employed the pH-sensitive ratiometric probe C-SNARF-4 to perform real-time microscopic analyses of the biofilm pH in response to salivary solutions containing glucose. Anaerobic glycolysis in the model biofilms created a mildly acidic environment. Decrease in pH in different areas of the biofilms varied, and distinct extracellular pH-microenvironments were conserved over several hours.

CONCLUSIONS/SIGNIFICANCE

The designed biofilm model represents a promising tool to determine the effect of potential therapeutic agents on biofilm growth, composition and extracellular pH. Ratiometric pH analysis using C-SNARF-4 gives detailed insight into the pH landscape of living biofilms and contributes to our general understanding of metabolic processes in in-vivo-grown bacterial biofilms.

Early microbial succession in redeveloping dental biofilms in periodontal health and disease

BACKGROUND AND OBJECTIVE

The development of dental biofilms after professional plaque removal is very rapid. However, it is not clear whether most bacterial species return at similar rates in periodontally healthy and periodontitis subjects or if there are differences in bacterial recolonization between supragingival and subgingival biofilms in periodontal health and disease.

MATERIAL AND METHODS

Supragingival and subgingival plaque samples were taken separately from 28 teeth in 38 healthy and 17 periodontitis subjects immediately after professional cleaning. Samples were taken again from seven teeth in randomly selected quadrants after 1, 2, 4 and 7 d of no oral hygiene and analyzed using checkerboard DNA-DNA hybridization. The percentage of DNA probe counts were averaged within subjects at each time-point. Ecological succession was determined using a modified moving-window analysis.

RESULTS

Succession in supragingival biofilms from subjects with periodontitis and from healthy individuals was similar. At 1 d, Streptococcus mitis and Neisseria mucosa showed increased proportions, followed by Capnocytophaga gingivalis, Eikenella corrodens, Veillonella parvula and Streptococcus oralis at 1-4 d. At 4-7 d, Campylobacter rectus, Campylobacter showae, Prevotella melaninogenica and Prevotella nigrescens became elevated. Subgingival plaque redevelopment was slower and very different from supragingival plaque redevelopment. Increased proportions were first observed for S. mitis, followed by V. parvula and C. gingivalis and, at 7 d, by Capnocytophaga sputigena and P. nigrescens. No significant increase in the proportions of periodontal pathogens was observed in any of the clinical groups or locations.

CONCLUSION

There is a defined order in bacterial species succession in early supragingival and subgingival biofilm redevelopment after professional cleaning.

The pathogenic persona of community-associated oral streptococci

The mitis group streptococci (MGS) are widespread in the oral cavity and are traditionally associated with oral health. However, these organisms have many attributes that contribute to the development of pathogenic oral communities. MGS adhere rapidly to saliva-coated tooth surfaces, thereby providing an attachment substratum for more overtly pathogenic organisms such as Porphyromonas gingivalis, and the two species assemble into heterotypic communities. Close physical association facilitates physiologic support, and pathogens such as Aggregatibacter actinomycetemcomitans display resource partitioning to favour carbon sources generated by streptococcal metabolism. MGS exchange information with community members through a number of interspecies signalling systems including AI-2 and contact dependent mechanisms. Signal transduction systems induced in P. gingivalis are based on protein dephosphorylation mediated by the tyrosine phosphatase Ltp1, and converge on a LuxR-family transcriptional regulator, CdhR. Phenotypic responses in P. gingivalis include regulation of hemin uptake systems and gingipain activity, processes that are intimately linked to the virulence of the organism. Furthermore, communities of S. gordonii with P. gingivalis or with A. actinomycetemcomitans are more pathogenic in animal models than the constituent species alone. We propose that MGS should be considered accessory pathogens, organisms whose pathogenic potential only becomes evident in the context of a heterotypic microbial community.

New cell surface protein involved in biofilm formation by Streptococcus parasanguinis

Dental biofilm formation is critical for maintaining the healthy microbial ecology of the oral cavity. Streptococci are predominant bacterial species in the oral cavity and play important roles in the initiation of plaque formation. In this study, we identified a new cell surface protein, BapA1, from Streptococcus parasanguinis FW213 and determined that BapA1 is critical for biofilm formation. Sequence analysis revealed that BapA1 possesses a typical cell wall-sorting signal for cell surface-anchored proteins from Gram-positive bacteria. No functional orthologue was reported in other streptococci. BapA1 possesses nine putative pilin isopeptide linker domains which are crucial for pilus assembly in a number of Gram-positive bacteria. Deletion of the 3' portion of bapA1 generated a mutant that lacks surface-anchored BapA1 and abolishes formation of short fibrils on the cell surface. The mutant failed to form biofilms and exhibited reduced adherence to an in vitro tooth model. The BapA1 deficiency also inhibited bacterial autoaggregation. The N-terminal muramidase-released-protein-like domain mediated BapA1-BapA1 interactions, suggesting that BapA1-mediated cell-cell interactions are important for bacterial autoaggregation and biofilm formation. Furthermore, the BapA1-mediated bacterial adhesion and biofilm formation are independent of a fimbria-associated serine-rich repeat adhesin, Fap1, demonstrating that BapA1 is a new streptococcal adhesin.

Novel model for multispecies biofilms that uses rigid gas-permeable lenses

Oral biofilms comprise complex multispecies consortia aided by specific inter- and intraspecies interactions occurring among commensals and pathogenic bacterial species. Oral biofilms are primary initiating factors of periodontal disease, although complex multifactorial biological influences, including host cell responses, contribute to the individual outcome of the disease. To provide a system to study initial stages of interaction between oral biofilms and the host cells that contribute to the disease process, we developed a novel in vitro model system to grow biofilms on rigid gas-permeable contact lenses (RGPLs), which enable oxygen to permeate through the lens material. Bacterial species belonging to early- and late-colonizing groups were successfully established as single- or three-species biofilms, with each group comprising Streptococcus gordonii, Streptococcus oralis, and Streptococcus sanguinis; S. gordonii, Actinomyces naeslundii, and Fusobacterium nucleatum; or S. gordonii, F. nucleatum, and Porphyromonas gingivalis. Quantification of biofilm numbers by quantitative PCR (qPCR) revealed substantial differences in the magnitude of bacterial numbers in single-species and multispecies biofilms. We evaluated cell-permeable conventional nucleic acid stains acridine orange, hexidium iodide, and Hoechst 33258 and novel SYTO red, blue, and green fluorochromes for their effect on bacterial viability and fluorescence yield to allow visualization of the aggregates of individual bacterial species by confocal laser scanning microscopy (CLSM). Substantial differences in the quantity and distribution of the species in the multispecies biofilms were identified. The specific features of these biofilms may help us better understand the role of various bacteria in local challenge of oral tissues.

Oral multispecies biofilm development and the key role of cell-cell distance

Growth of oral bacteria in situ requires adhesion to a surface because the constant flow of host secretions thwarts the ability of planktonic cells to grow before they are swallowed. Therefore, oral bacteria evolved to form biofilms on hard tooth surfaces and on soft epithelial tissues, which often contain multiple bacterial species. Because these biofilms are easy to study, they have become the paradigm of multispecies biofilms. In this Review we describe the factors involved in the formation of these biofilms, including the initial adherence to the oral tissues and teeth, cooperation between bacterial species in the biofilm, signalling between the bacteria and its role in pathogenesis, and the transfer of DNA between bacteria. In all these aspects distance between cells of different species is integral for oral biofilm growth.

Inhibition of Streptococcus mutans biofilm formation by Streptococcus salivarius FruA

The oral microbial flora consists of many beneficial species of bacteria that are associated with a healthy condition and control the progression of oral disease. Cooperative interactions between oral streptococci and the pathogens play important roles in the development of dental biofilms in the oral cavity. To determine the roles of oral streptococci in multispecies biofilm development and the effects of the streptococci in biofilm formation, the active substances inhibiting Streptococcus mutans biofilm formation were purified from Streptococcus salivarius ATCC 9759 and HT9R culture supernatants using ion exchange and gel filtration chromatography. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry analysis was performed, and the results were compared to databases. The S. salivarius HT9R genome sequence was determined and used to indentify candidate proteins for inhibition. The candidates inhibiting biofilms were identified as S. salivarius fructosyltransferase (FTF) and exo-beta-d-fructosidase (FruA). The activity of the inhibitors was elevated in the presence of sucrose, and the inhibitory effects were dependent on the sucrose concentration in the biofilm formation assay medium. Purified and commercial FruA from Aspergillus niger (31.6% identity and 59.6% similarity to the amino acid sequence of FruA from S. salivarius HT9R) completely inhibited S. mutans GS-5 biofilm formation on saliva-coated polystyrene and hydroxyapatite surfaces. Inhibition was induced by decreasing polysaccharide production, which is dependent on sucrose digestion rather than fructan digestion. The data indicate that S. salivarius produces large quantities of FruA and that FruA alone may play an important role in multispecies microbial interactions for sucrose-dependent biofilm formation in the oral cavity.

Point-of-care salivary microbial tests for detection of cariogenic species--clinical relevance thereof--review

Dental caries is a highly prevalent multifactorial disease that can result in serious health impairment. It was shown that oral bacteria play a significant role in caries development. Point-of-care (POC) salivary microbial tests for detection of cariogenic species have been investigated as a potential tool for caries risk assessment. This review aims to evaluate clinical relevance of these tests in the light of recent scientific evidence. Methodology involved PubMed search using key words salivary microbial tests, cariogenic bacteria and caries risk prediction. Articles obtained by the search were cross-referenced to obtain further sources. Specificity and negative-predictive value of these tests are higher than their sensitivity and positive value. Predictive power of the POC salivary microbial tests as a single predictor is generally weak, although it increases when included in multifactorial models for caries prediction. Literature findings support the use of these tests for screening of at-risk individuals in a population of young preschool children without visible caries and for motivation of subjects on individual level. POC salivary microbial tests are simple and inexpensive and, therefore, may be advantageous from public health perspective.

The Actinomyces oris type 2 fimbrial shaft FimA mediates co-aggregation with oral streptococci, adherence to red blood cells and biofilm development

Interbacterial interactions between oral streptococci and actinomyces and their adherence to tooth surface and the associated host cells are key early events that promote development of the complex oral biofilm referred to as dental plaque. These interactions depend largely on a lectin-like activity associated with the Actinomyces oris type 2 fimbria, a surface structure assembled by sortase (SrtC2)-dependent polymerization of the shaft and tip fimbrillins, FimA and FimB respectively. To dissect the function of specific fimbrillins in various adherence processes, we have developed a convenient new technology for generating unmarked deletion mutants of A. oris. Here, we show that the fimB mutant, which produced type 2 fimbriae composed only of FimA, like the wild type co-aggregated strongly with receptor-bearing streptococci, agglutinated with sialidase-treated red blood cells, and formed monospecies biofilm. In contrast, the fimA and srtC2 mutants lacked type 2 fimbriae and were non-adherent in each of these assays. Plasmid-based expression of the deleted gene in respective mutants restored adherence to wild-type levels. These findings uncover the importance of the lectin-like activity of the polymeric FimA shaft rather than the tip. The multivalent adhesive function of FimA makes it an ideal molecule for exploring novel intervention strategies to control plaque biofilm formation.

Exopolysaccharides produced by Streptococcus mutans glucosyltransferases modulate the establishment of microcolonies within multispecies biofilms

Streptococcus mutans is a key contributor to the formation of the extracellular polysaccharide (EPS) matrix in dental biofilms. The exopolysaccharides, which are mostly glucans synthesized by streptococcal glucosyltransferases (Gtfs), provide binding sites that promote accumulation of microorganisms on the tooth surface and further establishment of pathogenic biofilms. This study explored (i) the role of S. mutans Gtfs in the development of the EPS matrix and microcolonies in biofilms, (ii) the influence of exopolysaccharides on formation of microcolonies, and (iii) establishment of S. mutans in a multispecies biofilm in vitro using a novel fluorescence labeling technique. Our data show that the ability of S. mutans strains defective in the gtfB gene or the gtfB and gtfC genes to form microcolonies on saliva-coated hydroxyapatite surfaces was markedly disrupted. However, deletion of both gtfB (associated with insoluble glucan synthesis) and gtfC (associated with insoluble and soluble glucan synthesis) is required for the maximum reduction in EPS matrix and biofilm formation. S. mutans grown with sucrose in the presence of Streptococcus oralis and Actinomyces naeslundii steadily formed exopolysaccharides, which allowed the initial clustering of bacterial cells and further development into highly structured microcolonies. Concomitantly, S. mutans became the major species in the mature biofilm. Neither the EPS matrix nor microcolonies were formed in the presence of glucose in the multispecies biofilm. Our data show that GtfB and GtfC are essential for establishment of the EPS matrix, but GtfB appears to be responsible for formation of microcolonies by S. mutans; these Gtf-mediated processes may enhance the competitiveness of S. mutans in the multispecies environment in biofilms on tooth surfaces.

Structure and molecular characterization of Streptococcus pneumoniae capsular polysaccharide 10F by carbohydrate engineering in Streptococcus oralis

Although closely related at the molecular level, the capsular polysaccharide (CPS) of serotype 10F Streptococcus pneumoniae and coaggregation receptor polysaccharide (RPS) of Streptococcus oralis C104 have distinct ecological roles. CPS prevents phagocytosis of pathogenic S. pneumoniae, whereas RPS of commensal S. oralis functions as a receptor for lectin-like adhesins on other members of the dental plaque biofilm community. Results from high resolution NMR identified the recognition region of S. oralis RPS (i.e. Galfbeta1-6GalNAcbeta1-3Galalpha) in the hexasaccharide repeat of S. pneumoniae CPS10F. The failure of this polysaccharide to support fimbriae-mediated adhesion of Actinomyces naeslundii was explained by the position of Galf, which occurred as a branch in CPS10F rather than within the linear polysaccharide chain, as in RPS. Carbohydrate engineering of S. oralis RPS with wzy from S. pneumoniae attributed formation of the Galf branch in CPS10F to the linkage of adjacent repeating units through sub terminal GalNAc in Galfbeta1-6GalNAcbeta1-3Galalpha rather than through terminal Galf, as in RPS. A gene (wcrD) from serotype 10A S. pneumoniae was then used to engineer a linear surface polysaccharide in S. oralis that was identical to RPS except for the presence of a beta1-3 linkage between Galf and GalNAcbeta1-3Galalpha. This polysaccharide also failed to support adhesion of A. naeslundii, thereby establishing the essential role of beta1-6-linked Galf in recognition of adjacent GalNAcbeta1-3Galalpha in wild-type RPS. These findings, which illustrate a molecular approach for relating bacterial polysaccharide structure to function, provide insight into the possible evolution of S. oralis RPS from S. pneumoniae CPS.

Central role of the early colonizer Veillonella sp. in establishing multispecies biofilm communities with initial, middle, and late colonizers of enamel

Human dental biofilm communities comprise several species, which can interact cooperatively or competitively. Bacterial interactions influence biofilm formation, metabolic changes, and physiological function of the community. Lactic acid, a common metabolite of oral bacteria, was measured in the flow cell effluent of one-, two- and three-species communities growing on saliva as the sole nutritional source. We investigated single-species and multispecies colonization by using known initial, early, middle, and late colonizers of enamel. Fluorescent-antibody staining and image analysis were used to quantify the biomass in saliva-fed flow cells. Of six species tested, only the initial colonizer Actinomyces oris exhibited significant growth. The initial colonizer Streptococcus oralis produced lactic acid but showed no significant growth. The early colonizer Veillonella sp. utilized lactic acid in two- and three-species biofilm communities. The biovolumes of all two-species biofilms increased when Veillonella sp. was present as one of the partners, indicating that this early colonizer promotes mutualistic community development. All three-species combinations exhibited enhanced growth except one, i.e., A. oris, Veillonella sp., and the middle colonizer Porphyromonas gingivalis, indicating specificity among three-species communities. Further specificity was seen when Fusobacterium nucleatum (a middle colonizer), Aggregatibacter actinomycetemcomitans (a late colonizer), and P. gingivalis did not grow with S. oralis in two-species biofilms, but inclusion of Veillonella sp. resulted in growth of all three-species combinations. We propose that commensal veillonellae use lactic acid for growth in saliva and that they communicate metabolically with initial, early, middle, and late colonizers to establish multispecies communities on enamel.

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.

Mutualistic biofilm communities develop with Porphyromonas gingivalis and initial, early, and late colonizers of enamel

Porphyromonas gingivalis is present in dental plaque as early as 4 h after tooth cleaning, but it is also associated with periodontal disease, a late-developing event in the microbial successions that characterize daily plaque development. We report here that P. gingivalis ATCC 33277 is remarkable in its ability to interact with a variety of initial, early, middle, and late colonizers growing solely on saliva. Integration of P. gingivalis into multispecies communities was investigated by using two in vitro biofilm models. In flow cells, bacterial growth was quantified using fluorescently conjugated antibodies against each species, and static biofilm growth on saliva-submerged polystyrene pegs was analyzed by quantitative real-time PCR using species-specific primers. P. gingivalis could not grow as a single species or together with initial colonizer Streptococcus oralis but showed mutualistic growth when paired with two other initial colonizers, Streptococcus gordonii and Actinomyces oris, as well as with Veillonella sp. (early colonizer), Fusobacterium nucleatum (middle colonizer), and Aggregatibacter actinomycetemcomitans (late colonizer). In three-species flow cells, P. gingivalis grew with Veillonella sp. and A. actinomycetemcomitans but not with S. oralis and A. actinomycetemcomitans. Also, it grew with Veillonella sp. and F. nucleatum but not with S. oralis and F. nucleatum, indicating that P. gingivalis and S. oralis are not compatible. However, P. gingivalis grew in combination with S. gordonii and S. oralis, demonstrating its ability to overcome the incompatibility when cultured with a second initially colonizing species. Collectively, these data help explain the observed presence of P. gingivalis at all stages of dental plaque development.

Aggregatibacter actinomycetemcomitans builds mutualistic biofilm communities with Fusobacterium nucleatum and Veillonella species in saliva

Human oral bacterial pathogens grow in attached multispecies biofilm communities. Unattached cells are quickly removed by swallowing. Therefore, surface attachment is essential for growth, and we investigated multispecies community interactions resulting in mutualistic growth on saliva as the sole nutritional source. We used two model systems, saliva-coated transferable solid-phase polystyrene pegs (peg biofilms) and flow cells with saliva-coated glass surfaces. Fluorescent antibody staining and image analysis were used to quantify the biomass in flow cells, and quantitative real-time PCR with species-specific primers was used to quantify the biomass in peg biofilms. Veillonella sp. strain PK1910, Aggregatibacter actinomycetemcomitans JP2, and Fusobacterium nucleatum ATCC 10953 were unable to grow as single species in flow cells. Only A. actinomycetemcomitans grew after 36 h when peg biofilms remained submerged in saliva from the time of inoculation. Mixed-species coaggregates were used for two- and three-species inoculation. The biomass in two-species biofilms increased in both systems when Veillonella sp. strain PK1910 was present as one of the partners. Enhanced growth of all strains was observed in three-species biofilms in flow cells. Interestingly, in flow cells F. nucleatum and A. actinomycetemcomitans exhibited mutualism, and, although F. nucleatum was unable to grow with either of the other species in the peg system, F. nucleatum stimulated the growth of Veillonella sp. and together these two organisms increased the total biomass of A. actinomycetemcomitans in three-species peg biofilms. We propose that mutualistic two-species and multispecies oral biofilm communities form in vivo and that mutualism between commensal veillonellae and late colonizing pathogens, such as aggregatibacteria, contributes to the development of periodontal disease.

Fusobacterium nucleatum ATCC 10953 requires Actinomyces naeslundii ATCC 43146 for growth on saliva in a three-species community that includes Streptococcus oralis 34

Formation of dental plaque is a developmental process involving initial and late colonizing species that form polymicrobial communities. Fusobacteria are the most numerous gram-negative bacteria in dental plaque, but they become prevalent after the initial commensal colonizers, such as streptococci and actinomyces, have established communities. The unusual ability of these bacteria to coaggregate with commensals, as well as pathogenic late colonizers, has been proposed to facilitate colonization by the latter organisms. We investigated the integration of Fusobacterium nucleatum into multispecies communities by employing two in vitro models with saliva as the sole nutritional source. In flow cell biofilms, numbers of cells were quantified using fluorescently conjugated antibodies against each species, and static biofilms were analyzed by quantitative real-time PCR (q-PCR) using species-specific primers. Unable to grow as single-species biofilms, F. nucleatum grew in two-species biofilms with Actinomyces naeslundii but not with Streptococcus oralis. However, enhanced growth of fusobacteria was observed in three-species biofilms, indicating that there was multispecies cooperation. Importantly, these community dynamics yielded an 18-fold increase in the F. nucleatum biomass between 4 h and 18 h in the flow cell inoculated with three species. q-PCR analysis of static biofilms revealed that maximum growth of the three species occurred at 24 h to 36 h. Lower numbers of cells were observed at 48 h, suggesting that saliva could not support higher cell densities as the sole nutrient. Integration of F. nucleatum into multispecies commensal communities was evident from the interdigitation of fusobacteria in coaggregates with A. naeslundii and S. oralis and from the improved growth of fusobacteria, which was dependent on the presence of A. naeslundii.

Comparative structural and molecular characterization of ribitol-5-phosphate-containing Streptococcus oralis coaggregation receptor polysaccharides

The antigenically related coaggregation receptor polysaccharides (RPS) of Streptococcus oralis strains C104 and SK144 mediate recognition of these bacteria by other members of the dental plaque biofilm community. In the present study, the structure of strain SK144 RPS was established by high resolution NMR spectroscopy as [6Galfbeta1-6GalNAcbeta1-3Galalpha1-2ribitol-5-PO(4)(-)-6Galfbeta1-3Galbeta1](n), thereby indicating that this polysaccharide and the previously characterized RPS of strain C104 are identical, except for the linkage between Gal and ribitol-5-phosphate, which is alpha1-2 in strain SK144 versus alpha1-1 in strain C104. Studies to define the molecular basis of RPS structure revealed comparable genes for six putative transferases and a polymerase in the rps loci of these streptococci. Cell surface RPS production was abolished by disrupting the gene for the first transferase of strain C104 with a nonpolar erm cassette. It was restored in the resulting mutant by plasmid-based expression of either wcjG, the corresponding gene of S. pneumoniae for serotype 10A capsular polysaccharide (CPS) biosynthesis or wbaP for the transferase of Salmonella enterica that initiates O-polysaccharide biosynthesis. Thus, WcjG, like WbaP, appears to initiate polysaccharide biosynthesis by transferring galactose-1-phosphate to a lipid carrier. In further studies, the structure of strain C104 RPS was converted to that of strain SK144 by replacing the gene (wefM) for the fourth transferase in the rps locus of strain C104 with the corresponding gene (wcrC) of strain SK144 or Streptococcus pneumoniae serotype 10A. These findings identify genetic markers for the different ribitol-5-phosphate-containing types of RPS present in S. oralis and establish a close relationship between these polysaccharides and serogroup 10 CPSs of S. pneumoniae.