Noncanonical Streptococcus sanguinis ComCDE circuitry integrates environmental cues in transformation outcome decision

Natural competence is the principal driver of streptococcal evolution. While acquisition of new traits could facilitate rapid fitness improvement for bacteria, entry into the competent state is a highly orchestrated event, involving an interplay between various pathways. We present a new type of competence-predation coordination mechanism in Streptococcus sanguinis. Unlike other streptococci that mediate competence through the ComABCDE regulon, several key components are missing in the S. sanguinis ComCDE circuitry. We assembled two synthetic biology devices linking competence-stimulating peptide (CSP) cleavage and export with a quantifiable readout to unravel the unique features of the S. sanguinis circuitry. Our results revealed the ComC precursor cleavage pattern and the two host ABC transporters implicated in the export of the S. sanguinis CSP. Moreover, we discovered a ComCDE-dependent bacteriocin locus. Overall, this study presents a mechanism for commensal streptococci to maximize transformation outcome in a fluid environment through extensive circuitry rewiring.

Systematic functional analysis of the Com pilus in Streptococcus sanguinis: a minimalistic type 4 filament dedicated to DNA uptake in monoderm bacteria

IMPORTANCE

Type 4 filaments (T4F) are nanomachines ubiquitous in prokaryotes, centered on filamentous polymers of type 4 pilins. T4F are exceptionally versatile and widespread virulence factors in bacterial pathogens. The mechanisms of filament assembly and the many functions they facilitate remain poorly understood because of the complexity of T4F machineries. This hinders the development of anti-T4F drugs. The significance of our research lies in characterizing the simplest known T4F-the Com pilus that mediates DNA uptake in competent monoderm bacteria-and showing that four protein components universally conserved in T4F are sufficient for filament assembly. The Com pilus becomes a model for elucidating the mechanisms of T4F assembly.

PepO and CppA modulate Streptococcus sanguinis susceptibility to complement immunity and virulence

Streptococcus sanguinis is a ubiquitous commensal species of the oral cavity commonly involved as an opportunistic pathogen in cardiovascular infections. In this study, we investigated the functions of endopeptidase O (PepO) and a C3-degrading protease (CppA) in the systemic virulence of S. sanguinis. Isogenic mutants of pepO and cppA obtained in strain SK36 showed increased susceptibility to C3b deposition and to opsonophagocytosis by human polymorphonuclear neutrophils (PMN). These mutants differ, however, in their profiles of binding to serum amyloid P component (SAP) and C1q, whereas both showed reduced interaction with C4b-binding protein (C4BP) and/or factor H (FH) regulators as compared to SK36. The two mutants showed defects in ex vivo persistence in human blood, serum-mediated invasion of HCAEC endothelial cells, and virulence in a Galleria mellonella infection model. The transcriptional activities of pepO and cppA, assessed by RT-qPCR in nine wild-type strains, further indicated strain-specific profiles of pepO/cppA expression. Moreover, non-conserved amino acid substitutions were detected among the strains, mostly in CppA. Phylogenetic comparisons with homologues of streptococcal species of the oral and oropharyngeal sites suggested that S. sanguinis PepO and CppA have independent ancestralities. Thus, this study showed that PepO and CppA are complement evasion proteins expressed by S. sanguinis in a strain-specific manner, which are required for multiple functions associated with cardiovascular virulence.

Amyloid Fibrils Produced by Streptococcus sanguinis Contribute to Biofilm Formation and Immune Evasion

Bacterial surface proteins assembled into amyloids contribute to biofilm formation and host immune evasion. Streptococcus sanguinis, a pioneer colonizer of teeth commonly involved in cardiovascular infections, expresses about thirty-three proteins anchored to the cell wall by sortase A. Here, we characterized the production of amyloid in S. sanguinis strains differing in biofilm and immune evasion phenotypes and investigated the role of sortase A in amyloidogenesis. Amyloid was identified in biofilms formed by nine strains, using Congo red (CR) staining and cross-polarized light microscopy. Additionally, EGCG, an amyloid inhibitor, impaired biofilm maturation in a strain-specific fashion. The amounts of amyloid-like components quantified in culture fluids of nine strains using thioflavin T and fluorimetry negatively correlated with bacterial binding to complement-activating proteins (SAP, C1q), C3b deposition and rates of opsonophagocytosis in PMNs, implying amyloid production in immune evasion. The deletion of the sortase A gene (srtA) in strain SK36 compromised amyloid production and sucrose-independent biofilm maturation. The srtA mutant further showed increased susceptibility to C3b deposition and altered interactions with PMNs as well as reduced persistence in human blood. These findings highlight the contribution of amyloids to biofilm formation and host immune evasion in S. sanguinis strains, further indicating the participation of sortase A substrates in amyloidogenesis.

Antibacterial Activity of a Lysin LysP53 against Streptococcus mutans

Dental caries is a common disease affecting quality of life globally. In the present study, we found that a bacteriophage lysin LysP53 against Acinetobacter baumannii possesses selective activity on Streptococcus mutans, the main etiological agent of dental caries, even in low pH caries microenvironments, whereas only minor LysP53 activity was detected against Streptococcus sanguinis, Streptococcus oralis, and Streptococcus mitis. Testing activity against S. mutans planktonic cells showed that 4 μM LysP53 could kill more than 84% of S. mutans within 1 min in buffer with optimal pHs ranging from 4.0 to 6.5. Daily application of LysP53 on biofilms formed in BHI medium supplemented or not with sucrose could reduce exopolysaccharides, expression of genes related to acid resistance and adhesion, and the number of live bacteria in the biofilms. LysP53 treatment also showed similar effects as 0.12% chlorhexidine in preventing enamel demineralization due to S. mutans biofilms, as well as effective removal of S. mutans colonization of tooth surfaces in mice without observed toxic effects. Because of its selective activity against main cariogenic bacteria and good activity in low pH caries microenvironments, it is advantageous to use LysP53 as an active agent for preventing caries.

Environmental influences on Streptococcus sanguinis membrane vesicle biogenesis

Membrane vesicles are produced by Gram-negative and Gram-positive bacteria. While membrane vesicles are potent elicitors of eukaryotic cells and involved in cell-cell communication, information is scarce about their general biology in the context of community members and the environment. Streptococcus sanguinis, a Gram-positive oral commensal, is prevalent in the oral cavity and well-characterized for its ability to antagonize oral pathobionts. We have found that production and dissemination of membrane vesicles by S. sanguinis is dependent on environmental and community factors. Co-culture with interacting commensal Corynebacterium durum, as well as with the periodontal pathobiont Filifactor alocis had no effect on S. sanguinis vesicle number and size, whereas the periodontal pathobiont Porphyromonas gingivalis abolished S. sanguinis vesicle production. Using both correlation and differential expression analyses to examine the transcriptomic changes underlying vesicle production, we found that differential expression of genes encoding proteins related to the cytoplasmic membrane and peptidoglycan correlate with the abundance of membrane vesicles. Proteomic characterizations of the vesicle cargo identified a variety of proteins, including those predicted to influence host interactions or host immune responses. Cell culture studies of gingival epithelial cells demonstrated that both crude and highly purified membrane vesicles could induce the expression of IL-8, TNF-α, IL-1β, and Gro-α within 6 hours of inoculation at levels comparable to whole cells. Our findings suggest that production of membrane vesicles by S. sanguinis is heavily influenced by community and environmental factors and plays an important role in communication with host cells.

BacterAI maps microbial metabolism without prior knowledge

Training artificial intelligence (AI) systems to perform autonomous experiments would vastly increase the throughput of microbiology; however, few microbes have large enough datasets for training such a system. In the present study, we introduce BacterAI, an automated science platform that maps microbial metabolism but requires no prior knowledge. BacterAI learns by converting scientific questions into simple games that it plays with laboratory robots. The agent then distils its findings into logical rules that can be interpreted by human scientists. We use BacterAI to learn the amino acid requirements for two oral streptococci: Streptococcus gordonii and Streptococcus sanguinis. We then show how transfer learning can accelerate BacterAI when investigating new environments or larger media with up to 39 ingredients. Scientific gameplay and BacterAI enable the unbiased, autonomous study of organisms for which no training data exist.

Stoichiometric models of sucrose and glucose fermentation by oral streptococci: Implications for free acid formation and enamel demineralization

OBJECTIVES

The objective of this study is to develop stoichiometric models of sugar fermentation and cell biosynthesis for model cariogenic Streptococcus mutans and non-cariogenic Streptococcus sanguinis to better understand and predict metabolic product formation.

METHODS

Streptococcus mutans (strain UA159) and Streptococcus sanguinis (strain DSS-10) were grown separately in bioreactors fed brain heart infusion broth supplemented with either sucrose or glucose at 37 °C. Cell mass concentration and fermentation products were measured at different hydraulic residence times (HRT) to determine cell growth yield.

RESULTS

Sucrose growth yields were 0.080 ± 0.0078 g cell/g and 0.18 ± 0.031 g cell/g for S. sanguinis and S. mutans, respectively. For glucose, this reversed, with S. sanguinis having a yield of 0.10 ± 0.0080 g cell/g and S. mutans 0.053 ± 0.0064 g cell/g. Stoichiometric equations to predict free acid concentrations were developed for each test case. Results demonstrate that S. sanguinis produces more free acid at a given pH than S. mutans due to lesser cell yield and production of more acetic acid. Greater amounts of free acid were produced at the shortest HRT of 2.5 hr compared to longer HRTs for both microorganisms and substrates.

SIGNIFICANCE

The finding that the non-cariogenic S. sanguinis produces greater amounts of free acids than S. mutans strongly suggests that bacterial physiology and environmental factors affecting substrate/metabolite mass transfer play a much greater role in tooth or enamel/dentin demineralization than acidogenesis. These findings enhance the understanding of fermentation production by oral streptococci and provide useful data for comparing studies under different environmental conditions.

Genome-wide identification of Streptococcus sanguinis fitness genes in human serum and discovery of potential selective drug targets

Streptococcus sanguinis is a primary colonizer of teeth and is associated with oral health. When it enters the bloodstream, however, this bacterium may cause the serious illness infective endocarditis. The genes required for survival and proliferation in blood have not been identified. The products of these genes could provide a rich source of targets for endocarditis-specific antibiotics possessing greater efficacy for endocarditis, and also little or no activity against those bacteria that remain in the mouth. We previously created a comprehensive library of S. sanguinis mutants lacking every nonessential gene. We have now screened each member of this library for growth in human serum and discovered 178 mutants with significant abundance changes. The main biological functions disrupted in these mutants, including purine metabolism, were highlighted via network analysis. The components of an ECF-family transporter were required for growth in serum and were shown for the first time in any bacterium to be essential for endocarditis virulence. We also identified two mutants whose growth was reduced in serum but not in saliva. This strategy promises to enable selective targeting of bacteria based on their location in the body, in this instance, treating or preventing endocarditis while leaving the oral microbiome intact.

Synergism between Corynebacterium and Streptococcus sanguinis reveals new interactions between oral commensals

The oral microbiome engages in a diverse array of highly sophisticated ecological interactions that are crucial for maintaining symbiosis with the host. Streptococci and corynebacteria are among the most abundant oral commensals and their interactions are critical for normal biofilm development. In this study, we discovered that Streptococcus sanguinis specifically responds to the presence of Corynebacterium durum by dramatically altering its chain morphology and improving its overall fitness. By employing gas chromatography-mass spectrometry (GC-MS) analysis, specific fatty acids were identified in C. durum supernatants that are responsible for the observed effect. Membrane vesicles (MVs) containing these fatty acids were isolated from C. durum supernatants and were able to replicate the chain morphology phenotype in S. sanguinis, suggesting MV as a mediator of interspecies interactions. Furthermore, S. sanguinis responds to C. durum lipids by decreasing the expression of key FASII genes involved in fatty acid synthesis. Several of these genes are also essential for the chain elongation phenotype, which implicates a regulatory connection between lipid metabolism and chain elongation. In addition, C. durum was found to affect the growth, cell aggregation, and phagocytosis of S. sanguinis, revealing a complex association of these species that likely supports oral commensal colonization and survival.

Streptococcal Siglec-like adhesins recognize different subsets of human plasma glycoproteins: implications for infective endocarditis

Streptococcus gordonii and Streptococcus sanguinis are typically found among the normal oral microbiota but can also cause infective endocarditis. These organisms express cell surface serine-rich repeat adhesins containing "Siglec-like" binding regions (SLBRs) that mediate attachment to α2-3-linked sialic acids on human glycoproteins. Two known receptors for the Siglec-like adhesins are the salivary mucin MG2/MUC7 and platelet GPIbα, and the interaction of streptococci with these targets may contribute to oral colonization and endocarditis, respectively. The SLBRs display a surprising diversity of preferences for defined glycans, ranging from highly selective to broader specificity. In this report, we characterize the glycoproteins in human plasma recognized by four SLBRs that prefer different α2-3 sialoglycan structures. We found that the SLBRs recognize a surprisingly small subset of plasma proteins that are extensively O-glycosylated. The preferred plasma protein ligands for a sialyl-T antigen-selective SLBR are proteoglycan 4 (lubricin) and inter-alpha-trypsin inhibitor heavy chain H4. Conversely, the preferred ligand for a 3'sialyllactosamine-selective SLBR is glycocalicin (the extracellular portion of platelet GPIbα). All four SLBRs recognize C1 inhibitor but detect distinctly different glycoforms of this key regulator of the complement and kallikrein protease cascades. The four plasma ligands have potential roles in thrombosis and inflammation, and each has been cited as a biomarker for one or more vascular or other diseases. The combined results suggest that the interaction of Siglec-like adhesins with different subsets of plasma glycoproteins could have a significant impact on the propensity of streptococci to establish endocardial infections.

Streptococcus sanguis-induced platelet activation involves two waves of tyrosine phosphorylation mediated by FcγRIIA and αIIbβ3

The low-affinity IgG receptor, FcγRIIA, has been implicated in Streptococcus sanguis-induced platelet aggregation. Therefore, it is likely that signal transduction is at least partly mediated by FcγRIIA activation and a tyrosine kinase-dependent pathway. In this study the signal transduction mechanisms associated with platelet activation in response to the oral bacterium, S. sanguis were characterised. In the presence of IgG, S. sanguis strain 2017–78 caused the tyrosine phosphorylation of FcγRIIA 30s following stimulation, which led to the phosphorylation of Syk, LAT, and PLCγ2. These early events were dependent on Src family kinases but independent of either TxA2 or the engagement of the αIIbβ3 integrin. During the lag phase prior to platelet aggregation, FcγRIIA, Syk, LAT, and PLCγ2 were each dephosphorylated, but were re-phosphorylated as aggregation occurred. Platelet stimulation by 2017–78 also induced the tyrosine phosphorylation of PECAM-1, an ITIM-containing receptor that recruits protein tyrosine phosphatases. PECAM-1 co-precipitated with the protein tyrosine phosphatase SHP-1 in the lag phase. SHP-1 was also maximally tyrosine phosphorylated during this phase, suggesting a possible role for SHP-1 in the observed dephosphorylation events. As aggregation occurred, SHP-1 was dephosphorylated, while FcγRIIA, Syk, LAT, and PLCγ2 were rephosphorylated in an RGDS-sensitive, and therefore αIIbβ3-dependent, manner. Additionally, TxA2 release, 5-hydro-xytryptamine secretion and phosphatidic acid formation were all blocked by RGDS. Aspirin also abolished these events, but only partially inhibited αIIbβ3-mediated re-phosphorylation. Therefore, S.sanguis-bound IgG cross links FcγRIIA and initiates a signaling pathway that is down-regulated by PECAM-1-bound SHP-1. Subsequent engagement of αIIbβ3 leads to SHP-1 dephosphorylation permiting a second wave of signaling leading to TxA2 release and consequent platelet aggregation.

Is SpxA2 involved in hydrogen peroxide production and competence development in Streptococcus sanguinis?

PURPOSE

The objective of the present study was to investigate whether Streptococcus sanguinis SpxA2 plays a role in competence development and endogenous H2O2 generation, and whether the SpxA2 Cys10-XX-Cys13 (CXXC) motif is involved in competence development.

METHODOLOGY

The competence development of wild-type S. sanguinis (SK36) and its derivatives was compared by transformation efficiency assay and real-time RT-PCR. The spx allele mutants, spxA2 (C10A) and spxA2 (C13A), were constructed by site-directed mutagenesis. The Δpox mutant was treated with 1 mM H2O2 to exclude the effect of other Pox products on competence development.

RESULTS

Compared with the wild-type (4.42±0.58×10-4), the ΔspxA2 mutant showed decreased transformation efficiency (0.07±0.03×10-4). Furthermore, there was a 2- to 15-fold reduction in ΔspxA2 mutant com gene expression. SpxA2 was able to down-regulate endogenous H2O2 generation by repressing pox expression. Additionally, endogenous H2O2 negatively regulated competence without affecting spxA2 expression. The Δpox mutant increased com gene expression (2- to 8-fold), but the 1 mM H2O2-treated Δpox mutant showed decreased com gene expression. Interestingly, the ΔspxA2Δpox mutant showed enhanced competence-associated parameters. The fact that spxA2 (C10A) and spxA2 (C13A) behaved like the ΔspxA2 mutant revealed the role of the CXXC motif in competence development.

CONCLUSION

Although the intricate relationship between SpxA2, pox-mediated H2O2 production and competence development was clarified in S. sanguinis, it would be worthwhile to explore further whether H2O2 is involved in competence development through oxidizing the SpxA2 CXXC motif.

Salivary Receptors for the Proline-rich Protein-binding and Lectin-like Adhesins of Oral Actinomyces and Streptococci

Colonization of the tooth surface by actinomyces and viridans group streptococci involves the attachment of these bacteria to adsorbed salivary components of the acquired enamel pellicle. The hypothesis that this attachment depends on specific adhesins has now been assessed from the binding of bacteria with well-defined adhesive properties to blots of SDS-PAGE-separated parotid and submandibular-sublingual (SM-SL) saliva. Streptococcus sanguis and type 2 fimbriated Actinomyces naeslundii, which bound terminal sialic acid and Galβ1-3GalNAc, respectively, recognized only a few SM-SL salivary components, primarily MG2. In contrast, type 1 fimbriated A. naeslundii and S. gordonii, which bound purified proline-rich proteins (PRPs), recognized several other components from both SM-SL and parotid saliva. Significantly, bacteria that lacked PRP-binding and the lectin-like activities detected by binding to MG2 failed to bind any immobilized salivary component. These findings suggest the involvement of specific adhesins in bacterial recognition of many adsorbed salivary proteins and glycoproteins.

A combined cryo-EM and molecular dynamics approach reveals the mechanism of ErmBL-mediated translation arrest

Nascent polypeptides can induce ribosome stalling, regulating downstream genes. Stalling of ErmBL peptide translation in the presence of the macrolide antibiotic erythromycin leads to resistance in Streptococcus sanguis. To reveal this stalling mechanism we obtained 3.6-Å-resolution cryo-EM structures of ErmBL-stalled ribosomes with erythromycin. The nascent peptide adopts an unusual conformation with the C-terminal Asp10 side chain in a previously unseen rotated position. Together with molecular dynamics simulations, the structures indicate that peptide-bond formation is inhibited by displacement of the peptidyl-tRNA A76 ribose from its canonical position, and by non-productive interactions of the A-tRNA Lys11 side chain with the A-site crevice. These two effects combine to perturb peptide-bond formation by increasing the distance between the attacking Lys11 amine and the Asp10 carbonyl carbon. The interplay between drug, peptide and ribosome uncovered here also provides insight into the fundamental mechanism of peptide-bond formation.

Absence of capsule reveals glycan-mediated binding and recognition of salivary mucin MUC7 by Streptococcus pneumoniae

Salivary proteins modulate bacterial colonization in the oral cavity and interact with systemic pathogens that pass through the oropharynx. An interesting example is the opportunistic respiratory pathogen Streptococcus pneumoniae that normally resides in the nasopharynx, but belongs to the greater Mitis group of streptococci, most of which colonize the oral cavity. Streptococcus pneumoniae also expresses a serine-rich repeat (SRR) adhesin, PsrP, which is a homologue to oral Mitis group SRR adhesins, such as Hsa of Streptococcus gordonii and SrpA of Streptococcus sanguinis. As the latter bind to salivary glycoproteins through recognition of terminal sialic acids, we wanted to determine whether S. pneumoniae also binds to salivary proteins through possibly the same mechanism. We found that only a capsule-free mutant of S. pneumoniae TIGR4 binds to salivary proteins, most prominently to mucin MUC7, but that this binding was not mediated through PsrP or recognition of sialic acid. We also found, however, that PsrP is involved in agglutination of human red blood cells (RBCs). After removal of PsrP, an additional previously masked lectin-like adhesin activity mediating agglutination of sialidase-treated RBCs becomes revealed. Using a custom-spotted glycoprotein and neoglycoprotein dot blot array, we identify candidate glycan motifs recognized by PsrP and by the putative S. pneumoniae adhesin that could perhaps be responsible for pneumococcal binding to salivary MUC7 and glycoproteins on RBCs.

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.

Mitis group streptococci express variable pilus islet 2 pili

Background

Streptococcus oralis, Streptococcus mitis, and Streptococcus sanguinis are members of the Mitis group of streptococci and agents of oral biofilm, dental plaque and infective endocarditis, disease processes that involve bacteria-bacteria and bacteria-host interactions. Their close relative, the human pathogen S. pneumoniae uses pilus-islet 2 (PI-2)-encoded pili to facilitate adhesion to eukaryotic cells.

Methodology/Principal Findings

PI-2 pilus-encoding genetic islets were identified in S. oralis, S. mitis, and S. sanguinis, but were absent from other isolates of these species. The PI-2 islets resembled the genetic organization of the PI-2 islet of S. pneumoniae, but differed in the genes encoding the structural pilus proteins PitA and PitB. Two and three variants of pitA (a pseudogene in S. pneumoniae) and pitB, respectively, were identified that showed ≈20% difference in nucleotide as well as corresponding protein sequence. Species-independent combinations of pitA and pitB variants indicated prior intra- and interspecies horizontal gene transfer events. Polyclonal antisera developed against PitA and PitB of S. oralis type strain ATCC35037 revealed that PI-2 pili in oral streptococci were composed of PitA and PitB. Electronmicrographs showed pilus structures radiating >700 nm from the bacterial surface in the wild type strain, but not in an isogenic PI-2 deletion mutant. Anti-PitB-antiserum only reacted with pili containing the same PitB variant, whereas anti-PitA antiserum was cross-reactive with the other PitA variant. Electronic multilocus sequence analysis revealed that all PI-2-encoding oral streptococci were closely-related and cluster with non-PI-2-encoding S. oralis strains.

Conclusions/Significance

This is the first identification of PI-2 pili in Mitis group oral streptococci. The findings provide a striking example of intra- and interspecies horizontal gene transfer. The PI-2 pilus diversity provides a possible key to link strain-specific bacterial interactions and/or tissue tropisms with pathogenic traits in the Mitis group streptococci.

Diffusion of ofloxacin in the endocarditis vegetation assessed with synchrotron radiation UV fluorescence microspectroscopy

The diffusion of antibiotics in endocarditis vegetation bacterial masses has not been described, although it may influence the efficacy of antibiotic therapy in endocarditis. The objective of this work was to assess the diffusion of ofloxacin in experimental endocarditis vegetation bacterial masses using synchrotron-radiation UV fluorescence microspectroscopy. Streptococcal endocarditis was induced in 5 rabbits. Three animals received an unique IV injection of 150 mg/kg ofloxacin, and 2 control rabbits were left untreated. Two fluorescence microscopes were coupled to a synchrotron beam for excitation at 275 nm. A spectral microscope collected fluorescence spectra between 285 and 550 nm. A second, full field microscope was used with bandpass filters at 510–560 nm. Spectra of ofloxacin-treated vegetations presented higher fluorescence between 390 and 540 nm than control. Full field imaging showed that ofloxacin increased fluorescence between 510 and 560 nm. Ofloxacin diffused into vegetation bacterial masses, although it accumulated in their immediate neighborhood. Fluorescence images additionally suggested an ofloxacin concentration gradient between the vegetation peripheral and central areas. In conclusion, ofloxacin diffuses into vegetation bacterial masses, but it accumulates in their immediate neighborhood. Synchrotron radiation UV fluorescence microscopy is a new tool for assessment of antibiotic diffusion in the endocarditis vegetation bacterial masses.

Increased d-lactic Acid intestinal bacteria in patients with chronic fatigue syndrome

Patients with chronic fatigue syndrome (CFS) are affected by symptoms of cognitive dysfunction and neurological impairment, the cause of which has yet to be elucidated. However, these symptoms are strikingly similar to those of patients presented with D-lactic acidosis. A significant increase of Gram positive facultative anaerobic faecal microorganisms in 108 CFS patients as compared to 177 control subjects (p<0.01) is presented in this report. The viable count of D-lactic acid producing Enterococcus and Streptococcus spp. in the faecal samples from the CFS group (3.5 x 10(7) cfu/L and 9.8 x 10(7) cfu/L respectively) were significantly higher than those for the control group (5.0 x 10(6) cfu/L and 8.9 x 10(4) cfu/L respectively). Analysis of exometabolic profiles of Enterococcus faecalis and Streptococcus sanguinis, representatives of Enterococcus and Streptococcus spp. respectively, by NMR and HPLC showed that these organisms produced significantly more lactic acid (p<0.01) from (13)C-labeled glucose, than the Gram negative Escherichia coli. Further, both E. faecalis and S. sanguinis secrete more D-lactic acid than E. coli. This study suggests a probable link between intestinal colonization of Gram positive facultative anaerobic D-lactic acid bacteria and symptom expressions in a subgroup of patients with CFS. Given the fact that this might explain not only neurocognitive dysfunction in CFS patients but also mitochondrial dysfunction, these findings may have important clinical implications.

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.

Raman spectroscopic measurement of relative concentrations in mixtures of oral bacteria

Near-infrared Raman spectroscopy has been used for species identification of pure microbial specimens for more than a decade. More recently, this optical method has been extended to the analysis of specimens containing multiple species. In this report, we demonstrate rapid, reagent-free quantitative analysis of a simplified model of oral plaque containing three oral bacteria species, S. mutans, S. sanguis, and S. gordonii, using near-infrared Raman spectroscopy. Raman spectra were acquired from bacterial mixtures in 200 seconds. A prediction model was calibrated by the partial least squares method and validated by additional samples. On a scale from 0 to 1, relative fractions of each species could be predicted with a root mean square error of 0.07. These results suggest that near-infrared Raman spectroscopy is potentially useful in quantification of microbial mixtures in general and oral plaques in particular.

Plaque pH response to snack foods in children with different levels of mutans streptococci

This study aimed to investigate the effects of some snack foods on plaque pH in children with different levels of mutans streptococci (MS). Six children, aged 9-12 years, with low (<10(4)) and 6 children, aged 10-12 years, with high (>106) numbers of MS/ml saliva participated in the study. Dental plaque pH changes, after the consumption of milk chocolate, sweet biscuit, instant noodle, sticky rice with banana and a 10% sucrose positive control were measured using pH-electrode. The measurements of plaque pH were made on forty-eight-hour accumulated plaque, at baseline to determine the resting pH of the fasted plaque and at time intervals of 2, 5, 10, 20 and 30 minutes after food consumption. The plaque pH curves, delta pH values and area under curve for pH 6.0 for each test food were determined. Plaque acidogenicity was more pronounced for the high-MS group at almost all test periods compared to the low-MS group with all test foods. The test foods were ranked according to maximum pH drop in about the same order in both groups as follows: 10% sucrose > milk chocolate > sweet biscuit > sticky rice with banana > instant noodle. The plaque pH also stayed below pH 6.00 for a longer period in the high-MS group with sweet biscuit, milk chocolate, and sticky rice with banana. Findings suggest that pH responses were more acidic in high-MS group than low-MS group.

Photosensitization of in vitro biofilms by toluidine blue O combined with a light-emitting diode

In natural ecosystems, micro-organisms grow preferentially attached to surfaces, forming matrix-enclosed biofilms. The aim of this study was to determine photodestruction levels in biofilms after subjecting them to photodynamic therapy. Biofilms of Streptococcus mutans, S. sobrinus, and S. sanguinis were grown on enamel slabs for 3, 5 or 7 d. Both the number of viable micro-organisms and the concentration of water-insoluble polysaccharides were analysed, and mineral loss (DeltaZ) analyses were performed on the enamel slabs. The antimicrobial potential of toluidine blue O (0.1 mg ml(-1)), associated with 85.7 J cm(-2) of a light-emission diode, was evaluated on the viability of 5-d biofilms. Both the number of micro-organisms and the concentration of water-insoluble polysaccharide increased with the age of the biofilms. A significant reduction ( approximately 95%) in viability was observed for S. mutans and S. sobrinus biofilms following photosensitization, with a > 99.9% reduction in the viability of S. sanguinis biofilms. In conclusion, a biofilm model was shown to be suitable for studying changes in bacterial numbers and enamel mineralization and for demonstrating the potential value of photosensitization in the control of in vitro biofilms.

Surface free energy and bacterial retention to saliva-coated dental implant materials--an in vitro study

The aim of the present investigation was to compare the in vitro bacterial retention on saliva-coated implant materials (pure titanium grade 2 (cp-Ti) and a titanium alloy (Ti-6Al-4V) surfaces), presenting similar surface roughness, and to assess the influence of physico-chemical surface properties of bacterial strain and implant materials on in vitro bacterial adherence. Two bacterial strains (one hydrophilic strain and one hydrophobic strain) were used and the following were evaluated: bacterial cell adherence, SFE values as well as the Lifshitz-van-der Waals, the Lewis acid base components of SFE, the interfacial free energy and the non-dispersive interactions according to two complementary contact angle measurement methods: the sessile drop method and the captive bubble method. Our results showed similar patterns of adherent bacterial cells on saliva-coated cp-Ti and saliva-coated Ti-6Al-4V. These findings could suggest that bacterial colonization (i.e. plaque formation) is similar on saliva-coated cp-Ti and Ti-6Al-4V surfaces and indicate that both materials could be suitable for use as transgingival abutment or healing implant components. The same physico-chemical properties exhibited by saliva-coated cp-Ti and TA6V, as shown by the sessile drop method and the captive bubble method, could explain this similar bacterial colonisation. Therefore, higher values of total surface free energy of saliva-coated cp-Ti and saliva-coated TA6V samples (gamma(SV) approximately 65mJ/m(2)) were reported using the captive bubble method indicating a less hydrophobic character of these surfaces than with the sessile drop method (gamma(S) approximately 44.50mJ/m(2)) and consequently possible differences in oral bacterial retention according the theory described by Absolom et al. The number of adherent hydrophobic S. sanguinis cells was two-fold higher than that of hydrophilic S. constellatus cells. Our results confirm that physico-chemical surface properties of oral bacterial strains play a role in bacterial retention to implant materials in the presence of adsorbed salivary proteins.

A serine-rich glycoprotein of Streptococcus sanguis mediates adhesion to platelets via GPIb

Streptococcus sanguis is the most common oral bacterium causing infective endocarditis and its ability to adhere to platelets, leading to their activation and aggregation, is thought to be an important virulent factor. Previous work has shown that S. sanguis can bind directly to platelet glycoprotein (GP) Ib but the nature of the adhesin was unknown. Here, we have shown that a high molecular weight glycoprotein of S. sanguis mediates adhesion to glycocalacin. The bacterial glycoprotein was purified from cell extracts by chromatography on GPIb- and wheatgerm agglutinin affinity matrices and its interaction with GPIb was shown to be sialic acid-dependent. We designated the glycoprotein serine-rich protein A (SrpA). An insertional inactivation mutant lacking the SrpA of S. sanguis showed significantly reduced binding to glycocalacin, reduced adherence to platelets and a prolonged lag time to platelet aggregation. In addition, under flow conditions, platelets rolled and subsequently adhered on films of wild-type S. sanguis cells at low shear (50/s) but did not bind to films of the SrpA mutant. Platelets did not bind to wild-type bacterial cells at high shear (1500/s). These findings help to understand the mechanisms by which the organism might colonize platelet-fibrin vegetations.

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

OBJECTIVE

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

DESIGN

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

RESULTS

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

CONCLUSIONS

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

Real-time interaction of oral streptococci with human salivary components

Oral streptococci are present in large numbers in dental plaque and several types interact with the enamel salivary pellicle to form a biofilm on tooth surfaces. The respective affinity of individual streptococci for salivary components has an influence on the etiologic properties of oral biofilm in the development of dental caries. We studied real-time biospecific interactions between oral streptococci and salivary components utilizing biosensor technology to analyze surface plasmon resonance. Streptococcus sanguis and Streptococcus mutans showed significant responses for binding to salivary components, in comparison with other bacteria. Further, the association rates (4.1 x 10-11/bacterium) and dissociation rate (5.7 +/- 0.9 x 10-3 Second(s)-1) were higher for S. sanguis than for S. mutans (2.4 x 10-11 and 2.9 +/- 0.8 x 10-3) and Streptococcus mitis (1.3 x 10-11 and 3.5 +/- 1.3 x 10-3). However, the association equilibrium constants (8.2 S/bacterium) for S. mutans was 2 times higher in than S. mitis (3.8) and slightly higher than S. sanguis (7.2). These findings may provide useful information regarding the mechanism of early biofilm formation by streptococci on the tooth surface.

Glucan-binding proteins of the oral streptococci

The synthesis of extracellular glucan is an integral component of the sucrose-dependent colonization of tooth surfaces by species of the mutans streptococci. In investigators' attempts to understand the mechanisms of plaque biofilm development, several glucan-binding proteins (GBPs) have been discovered. Some of these, the glucosyltransferases, catalyze the synthesis of glucan, whereas others, designated only as glucan-binding proteins, have affinities for different forms of glucan and contribute to aspects of the biology of their host organisms. The functions of these latter glucan-binding proteins include dextran-dependent aggregation, dextranase inhibition, plaque cohesion, and perhaps cell wall synthesis. In some instances, their glucan-binding domains share common features, whereas in others the mechanism for glucan binding remains unknown. Recent studies indicate that at least some of the glucan-binding proteins modulate virulence and some can act as protective immunogens within animal models. Overall, the multiplicity of GBPs and their aforementioned properties are testimonies to their importance. Future studies will greatly advance the understanding of the distribution, function, and regulation of the GBPs and place into perspective the facets of their contributions to the biology of the oral streptococci.

Fluoride and organic weak acids as respiration inhibitors for oral streptococci in acidified environments

Oxygen metabolism (respiration) of Streptococcus mutans GS-5 involving NADH oxidases, mainly of the H(2)O-producing type, was found to be acid sensitive, as was NADH oxidase activity of cell extracts. Respiration of intact cells in acidified media was also highly sensitive to fluoride, with a 50% inhibitory concentration of about 0.02 mM at pH 4. In contrast, NADH oxidases in cell extracts were fluoride insensitive. Fluoride inhibition of respiration of intact cells was related to weak-acid effects leading to enhanced proton permeability of cells, cytoplasmic acidification and resultant acid inhibition of NADH oxidases and glycolysis. Organic weak acids, such as indomethacin and benzoate, were also effective inhibitors. H(2)O(2) production by intact cells of Streptococcus sanguis NCTC 10904, a peroxide producer, was similarly inhibited by fluoride or organic weak acids in acidified media. Thus, weak acids act as respiratory inhibitors for oral streptococci indirectly by acidifying the cytoplasm rather than acting as direct inhibitors of NADH oxidases.

Effects of glucose and fluoride on competition and metabolism within in vitro dental bacterial communities and biofilms

Antimicrobial effects of fluoride in vivo remain contentious. Previous studies suggested that 1 mM NaF reduced acid production from glucose, and prevented the enrichment of bacteria associated with caries in a chemostat model. The present study examines the effects of a lower fluoride concentration (0.53 mM, 10 ppm NaF) in both biofilm and planktonic microbial communities. Nine oral species were grown at pH 7.0 and pulsed on 10 successive days with glucose; bacterial metabolism was allowed to reduce the pH for 6 h before being returned to neutrality, either in the presence or absence of NaF. In addition, 10-day-old mixed culture biofilms were overlaid with glucose, with or without NaF, and the pH change followed by microelectrode. After 10 days, chemostat pH dropped to ca. pH 4.5 following glucose pulses, and the community was dominated by Streptococcus mutans (rising from 4 to 23% of total CFU) and Veillonella dispar (16 to 73%). In comparison, after 10 days pulsing with glucose + fluoride, the final pH was significantly higher (ca. pH 4.9) (paired t test, p < 0.0001). The culture was predominated by V. dispar (70%) and Actinomyces naeslundii (13%), whereas S. mutans proportions were significantly lower (t test, p = 0.04), remaining <3% of the total flora, compared to the culture without fluoride. Biofilm pH fell to only pH 5.55 1 h after glucose/fluoride overlay, compared to 4.55 with glucose alone (paired t test, p < 0.000001). Analysis of the data suggests that fluoride exerts dual antimicrobial modes of action. Fluoride prevents enrichment of S. mutans by inhibiting critical metabolic processes (direct effect) and, in an inter-related way, by reducing environmental acidification (indirect effect) in biofilms.

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

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

[Pyruvate oxidase gene from Streptococcus sanguis: molecular cloning and sequence analysis of the gene]

OBJECTIVE

To clone and sequence the gene of pyruvate oxidase (Sopox) from Streptococcus sanguis.

METHODS

The PCR primers for Sopox gene were designed and synthesized according to the sequence of pyruvate oxidase (spxB) gene of S. pneumonia. The amplified PCR product was cloned into pUC18 and then subcloned into M13mp18 and M13mp19. The DNA sequence of the gene was analyzed.

RESULTS

Sopox gene was successfully amplified from S. sanguis ATCC10557. The nucleotide sequence of the whole gene was revealed to be 1788 base pairs with one open reading frame coding pyruvate oxidase with 591 amino acid residuals.

CONCLUSION

The clone and DNA sequence of Sopox gene were obtained which could serve as a foundation on which to elucidate the molecular mechanisms of hydrogen peroxide production and its regulation by oral streptococci.

Binding of oral streptococci to human fibrinogen

The interaction of oral streptococci with human fibrinogen was investigated. Streptococcus gordonii was chosen as a representative species to study the binding to fibrinogen. S. gordonii DL1 adhered to immobilized fibrinogen and bovine serum albumin. Binding to immobilized fibrinogen was saturable, concentration and temperature dependent. The binding of S. gordonii DL1 to fibrinogen was inhibited by anti-fibrinogen antibody. Heating of the bacteria for 1 h at 95 degrees C resulted in 90% inhibition of the binding. Trypsin treatment of the bacteria resulted in decreased binding. Neither lipoteichoic acid nor culturing of the bacteria in a sucrose-supplemented medium had any effect on the binding. S. gordonii, Streptococcus sanguinis, Streptococcus mitis, and Streptococcus oralis bound to the immobilized fibrinogen, but mutans streptococci did not. None of the oral streptococci tested bound to the fibrinogen in fluid phase. These results suggest that the binding of S. gordonii DL1 to immobilized fibrinogen is mediated through a specific protein adhesin-receptor interaction, and fibrinogen acts as a cryptitope.

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

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

Strain-related acid production by oral streptococci

Acid production, in particular at low pH, is thought to be an important ecological determinant in dental caries. The aim of the present study was to determine the acid producing capability at different pH levels of 47 streptococcal strains, representing 9 species, isolated from human dental plaque. The bacteria were grown until mid log-phase under anaerobic conditions and acid production was measured in a pH-stat system at pH 7.0, 6.0, 5.5 and 5.0. At all pH values, the mean velocity of acid production (V(ap)) by Streptococcus mutans and S. sobrinus was significantly higher (p<0.01; ANOVA) than that of the other oral streptococci, including S. mitis, S. oralis, S. gordonii, S. sanguis, S. intermedius, S. anginosus, S. constellatus, and S. vestibularis. However, the V(ap) of some strains of S. mitis biovar 1 and S. oralis, particularly at pH values of 7.0 and 6.0, exceeded that of some strains of S. mutans. The V(ap) decreased with pH for all strains, but some strains of S. mitis biovar 1 and strains of the mutans streptococci maintained a relatively high rate of acid production. The results suggest that some strains of S. mitis biovar 1 and S. oralis may play an important role in caries development by modifying the environment in dental plaque to become favourable for the succession of aciduric species. The study furthermore emphasises the need for detailed species and biovar identification of oral streptococci and for recognition of the significant physiological differences that occur within single species.

[A comparative study on the capacities of different strains of Streptococcus sanguis for P-aminobenzoic acid production]

This study was intended to compare the capacities of different strains of Strep, sanguis for P-Aminobenzoic acid (PABA) production. The synthesis of PABA during the growth of four strains of Strep. sanguis was measured by the reversed-phase high-performance liquid chromatographic method. The results showed that the concentrations of PABA synthesized by S. sanguis 10556, S. sanguis 10557, S. sanguis S34 and S. sanguis H7-4. Were 1.979 +/- 0.081 micrograms/ml, 1.383 +/- 0.193 micrograms/ml, 1.983 +/- 0.052 micrograms/ml and 1.032 +/- 0.229 micrograms/ml, respectively, and in term of PABA concentration, S. sanguis 10556 was significantly different from S. sanguis 10557 and S. sanguis H7-4; S. sanguis S34 was significantly different from S. sanguis 10557 and S. sanguis H7-4. No significant difference was found between S. sanguis 10556 and S. sanguis S34, nor between S. sanguis 10557 and S. sanguis H7-4, either. In conclusion, the method is simple, rapid and accurate. S. sanguis did synthesize PABA, and the difference in ability for PABA formation existed among the four strains of S. sanguis. This study is helpful to researches on the symbiosis between S. sanguis and S. muntans and to determination of their role in the microbial homeostasis of dental plaque.

Studies concerning the glucosyltransferase of Streptococcus sanguis

We have shown in previous studies that the glucosyltransferase (Gtf) enzymes of Streptococcus mutans have distinct properties when adsorbed to a surface. In the present study, we compared the activity of Gtf from Streptococcus sanguis, designated GtfSs, in solution and on the surface of saliva-coated hydroxyapatite (sHA) beads, and determined the ability of its product glucan to support the adherence of oral microorganisms. Gtf from S. sanguis 804 NCTC 10904 was purified from culture supernatant fluids by means of hydroxyapatite chromatography. Enzyme and the substrate were prepared in buffers at pH values from 3.5 to 7.5. Maximum activity of GtfSs occurred between pH 5.5 and pH 6.5, whether in solution or adsorbed onto a surface. The solubilized and insolubilized enzymes showed highest activity at 40 degrees C; activity was reduced by 50(+/-2)% at 20 and 30 degrees C. The enzyme did not form glucans in either phase at 10 or 60 degrees C. The K(m), determined from Lineweaver-Burk plots, for the enzyme in solution was 4.3(+/-0.4) mmol/l sucrose, and the K(m) for the enzyme on sHA beads was 5.0(+/-1.0) mmol/l sucrose. The ability of the GtfSs glucan synthesized on the surface of sHA beads to support the adherence of oral bacteria was investigated. (3)H-thymidine-labeled bacteria (S. mutans GS-5, S. sobrinus 6715, S. sobrinus 6716, S. sanguis 10904, Actinomyces viscosus OMZ105E, A. viscosus 2085, and A. viscosus 2086) were incubated with sHA beads coated with GtfSs glucan. S. mutans GS-5 displayed the highest level of binding numerically. These results show that the GtfSs of S. sanguis is active on sHA beads, that the pH optimum for activity on a surface differs slightly from that in solution, and that its product glucan can support the adherence of oral microorganisms.

Reversed-phase high-performance liquid chromatographic measurement of the P-aminobenzoic acid synthesized by Streptococcus sanguis

OBJECTIVE

This study investigated the biosynthesis of P-aminobenzoic acid by Streptococcus sanguis and the role of P-aminobenzoic acid in the interaction between Streptococcus sanguis and Streptococcus mutans.

METHODS

A reversed-phase high-performance liquid chromatographic technique was used to analyze the P-aminobenzoic acid synthesized by Streptococcus sanguis in an anaerobic atmosphere.

RESULTS

The results showed, that (1) the chromatographic method established in this study had good linear relation and the average recovery of P-aminobenzoic acid was 80%, and (2) Streptococcus sanguis did synthesize P-aminobenzoic acid, and the mean concentration of P-aminobenzoic acid was 1.23 micrograms/mL.

CONCLUSIONS

The results of this study will help further studies of the factors that may have effects on P-aminobenzoic acid synthesis by Streptococcus sanguis and on the role of P-aminobenzoic acid in the microbial homeostasis of dental plaque.

[Study on the biosynthesis of para-aminobenzoic acid by S. sanguis. II. Qualitative and quantitative analysis]

In this study, the method established in paper 1 was used to analyze PABA synthesized by S. sanguis S34. The results showed: 1. S. sanguis S34 did synthesize PABA and the mean concentration of PABA was 1.236 micrograms/ml. 2. the components had good linear relation and average recovery was 80%. The results of this paper will be helpful to studying influencing factors on PABA synthesis of S. sanguis and the roles of PABA in microbial homeostasis of dental plaque.

[Study on the biosynthesis of para-aminobenzoic acid by S. sanguis. I. Establishment of a reversed-phase high-performance liquid chromatography]

In order to study the synthesis of para-aminobenzoic acid (PABA) by S. mutans and the role of PABA in the interaction between S. mutans and S. sanguis, a reversed-phase high-performance liquid chromatography (RP-HPLC) for analysis of PABA was developed. The results showed that the optimal chromatographic parameters were flow rate of 1.5 ml/min, T = 55 +/- 2 degrees C, methanol/phosphate buffer of 10/90(by vol) (pH 2.2 0.1 mol/L), m-hydroxybenzoic acid as an internal standard. The method is simple, rapid accurate and useful.

Thermophysiology of Streptococcus mutans and related lactic-acid bacteria

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

Effects of acidification on growth and glycolysis of Streptococcus sanguis and Streptococcus mutans

After carbohydrate intake, pH in dental plaque decreases rapidly and reaches about 4 within a few minutes. The acidification not only promotes demineralization of tooth surface but can also cause damage to bacteria in dental plaque. We, therefore, investigated the effect of acidification on the dental plaque bacteria Streptococcus sanguis and Streptococcus mutans. At pH 4.0 and 4.2, both growth and glycolytic activities in these streptococci were repressed. Prolonged acidification (for 60 min at pH 4.0) not only repressed both growth and glycolytic activities but also impaired them in S. sanguis cells with concomitant inactivation of the glycolytic enzymes, hexokinase, phosphofructokinase, glyceraldehydephosphate dehydrogenase and enolase. The impaired abilities of glycolysis and growth recovered following incubation at pH 7.0 for 80-90 min, and this was accompanied by reactivation of the glycolytic enzymes. On the other hand, these impairments were not observed in S. mutans cells exposed to prolonged acidification. These results indicate that the low pH frequently occurring in dental plaque may transiently impair streptococcal glycolysis and growth and that S. mutans is more durable to the acidification than S. sanguis.

Differential toxic effects of lactate and acetate on the metabolism of Streptococcus mutans and Streptococcus sanguis

Experiments were conducted with Streptococcus mutans NCTC 10449 and Streptococcus sanguis ATCC 10556 to determine whether the acid end-products, lactate and acetate, were involved in the regulation of cellular growth and metabolism. The growth rate and culture biomass of both organisms was inhibited by the addition of lactate and acetate at concentrations as high as 200 mM to the cultures, although the final pH values of the lactate and acetate cultures were similar. In addition, the metabolic conversion of glucose to lactate was decreased by external lactate but stimulated by acetate. In spite of this, calculation of the yield of cell biomass per mole of ATP (YATP) showed that the yield of both organisms actually increased in the presence of added lactate, but decreased with acetate. This indicates that the two acids interacted with the cells of the organisms by different mechanisms. For both organisms, the final external undissociated lactic acid was relatively constant at concentrations between 0 and 200 mM added lactate, 24.9-32.5 mM for S. mutans and 8.0-11.5 mM for S. sanguis. On the other hand, the final concentration of undissociated acetic acid in the S. mutans cultures increased from 2.9 to 83.7 mM as the medium acetate concentration increased, and from 1.0 to 36.0 mM with the S. sanguis cultures. Counterflow experiments provided evidence for a lactate carrier in both S. mutans and S. sanguis, but an acetate carrier in these organisms could not be demonstrated. [14C]-lactate and [14C]-acetate were taken up into de-energized, chemostatgrown cells of S. mutans and S. sanguis in response to an artificially generated pH gradient but not by an imposed electrical gradient. Thus, under these conditions lactate uptake occurred via a symport process with only one proton. Growth of both organisms in the presence of increasing concentrations of acetate resulted in a small reduction (27%) in the transmembrane pH gradient (delta pH) as measured by the permeant acid, [14C]-salicylate. However, the uptake of [14C]-acetate for the estimation of delta pH revealed significant inhibition of the acetate concentration gradient in the presence external acetate, indicating that the cells expelled the acetate anion. The results indicate that, unlike acetate uptake, lactate transport by S. mutans and S. sanguis was strictly regulated via the lactate carrier in order to prevent excessive dissipation of the pH gradient. Clearly, the formation of acetate by oral streptococci is more problematic for cellular homeostasis than the formation of lactate.

Utilization of sialic acid by viridans streptococci

The importance of viridans streptococci as agents of serious extra-oral diseases, including endocarditis, is now recognized. We have tested the hypothesis that the ability to utilize sialic acid as a nutrient source may play a role in the proliferation of these organisms. The type strains of the 15 presently recognized species of viridans streptococci and two clinical isolates-S. oralis (AR3), isolated from a patient with infective endocarditis, and S. intermedius (UNS35), a brain abscess isolate-were studied for their ability to utilize sialic acid. Only S. oralis, S. sanguis, S. gordonii, S. mitis ("oralis group") S. intermedius, S. anginosus, S. constellatus ("milleri group"), and S. defectivus ("nutritionally variant group") were able to use sialic acid (N-acetylneuraminic acid) efficiently as a sole carbon source. Formate, acetate, and ethanol were produced as the major metabolic end-products of sialic acid metabolism, while corresponding glucose-grown cultures produced lactate as the major metabolic end-product. Utilization of sialic acid was independent of the production of sialidase. Cell-free extracts of sialic acid-grown cultures expressed elevated levels of N-acetylneuraminate pyruvate-lyase (NPL; the first enzyme in the intracellular catabolism of sialic acid) and N-acetylglucosamine-6-phosphate (GlcNAc-6-P) deacetylase and glucosamine-6-phosphate (GlcN-6-P) deaminase (enzymes involved in the intracellular catabolism of N-acetylglucosamine). These activities were repressed by growth in the presence of glucose. The intracellular fate of sialic acid, after cleavage by NPL into N-acetylmannosamine (ManNAc) and pyruvate, is uncertain, but the elevated levels of GlcNAc-6-P deacetylase and GlcN-6-P deaminase in sialic acid-grown cells suggest that phosphorylation and isomerization are possible steps in the metabolism of ManNAc to generate an intermediate common to the pathway of N-acetylglucosamine metabolism. The species of viridans streptococci that have the ability to utilize sialic acid are those most commonly associated with extra-oral diseases, and this ability is likely to play a role in the persistence and survival of these infecting organisms in vivo.

Competitive binding of calcium, magnesium and zinc to Streptococcus sanguis and purified S. sanguis cell walls

Calcium bound by oral bacteria may have important effects on plaque cohesion and mineral dynamics. Equilibrium dialysis was used here to study the effect of magnesium and zinc competition on calcium-binding by Streptococcus sanguis 7863. Experiments were carried out using 45Ca in 0.1-5.0 mmol/l Ca2+ carrier. Increasing [Mg] and [Zn] decreased the apparent Ca-binding affinity, allowing calculation of the affinities for Mg2+ and Zn2+. Dissociation constants were found to be 0.94 +/- 0.23, 1.32 +/- 0.39 and 1.26 +/- 0.41 mmol/l (whole cells) and 1.87 +/- 0.49, 3.05 +/- 1.24 and 4.08 +/- 1.29 mmol/l (cell walls), for Ca, Mg and Zn respectively. Binding capacities for Ca (and, by inference, Mg and Zn) were 27.7 +/- 2.8 mumol/g wet weight (whole cells) and 54.2 +/- 1.6 mumol/g wet weight (cell walls). These data suggest that Mg and Zn act as true competitive inhibitors of calcium binding.

Simultaneous monitoring of intracellular pH and proton excretion during glycolysis by Streptococcus mutans and Streptococcus sanguis: effect of low pH and fluoride

A system was developed by which 2',7'-bis(carboxyethyl)-4 or 5-carboxyfluorescein could be used to monitor intracellular pH at the same time that proton excretion was being measured. Streptococcal cells were loaded with the dye, and after the addition of glucose protons were excreted and the intracellular pH increased quickly and remained higher than the extracellular pH of 7.0. The excretion of protons stopped and the intracellular pH returned to the original level when glucose was depleted. The intracellular level of ATP remained high during glucose metabolism and decreased with the depletion of glucose. At extracellular pH of 5.5, and 5.0, the intracellular pH of fasting cells was higher than the extracellular pH value. After addition of glucose there were initial lags of proton excretion and of increases in intracellular pH at the acidic extracellular pH values. In the presence of fluoride, a lag in proton excretion and a simultaneous decrease in intracellular pH were observed, indicating a partial and transient inhibition of proton-ATPase activity.

Modulation of glycosidase and protease activities by chemostat growth conditions in an endocarditis strain of Streptococcus sanguis

The effects of growth conditions on the properties of the endocarditis-producing oral bacterium Streptococcus sanguis FSS2 were studied. This strain produces a variety of proteases and glycosidases, including a thrombin-like activity that is a potential virulence factor for endocarditis. Cultures were grown with limiting glucose or galactose in chemostats over a range of dilution rates and pH levels, and the following activities were measured at pH 7.5: thrombin-like, Hageman factor-like, N-acetyl-beta-D-galactosaminidase, beta-D-glucosidase, and beta-D-galactosidase. At growth pH 6.5, specific activities generally decreased as the dilution rate increased from 0.05 to 0.40 h(-1). At a dilution rate of 0.1 h(-1), specific activities generally were highest at growth pH 6.5 and lower and approximately equal at growth pH 5.5 and 7.5. The major exception was the thrombin-like activity, for which the specific activity at growth pH 7.5 was approximately 5-fold higher than at growth pH 5.5. Hageman factor-like activity was apparently glucose catabolite repressible, as its activity was 3-fold higher in galactose cultures. The measured activities changed as functions of growth conditions and thus were modulated by environment. Environmental regulation of thrombin-like activity by pH is consistent with an activity that is less important on tooth surfaces than in tissues.

Degradation and fermentation of fructo-oligosaccharides by oral streptococci

Fructo-oligosaccharides (FOS) are claimed to have a positive effect on the intestinal flora. They are being used in functional foods in Japan and Europe. This group have tested the degradation of two commercial FOS preparations by oral streptococci in order to predict the cariogenicity of these products. Both preparations could be fermented to some extent by the species of oral streptococci tested. The enzymes necessary for the degradation of FOS were inducible. Each strain showed a specific degradation pattern. All strains, particularly Streptococcus mutans rapidly produced acid, mainly lactic acid. Streptococcus mitis also produced high concentrations of acetic acid. Plaque formation by Strep. mutans was similar to the sucrose control. It is concluded that FOS are cariogenic to a similar extent as sucrose.