Communication among oral bacteria

Human oral bacteria interact with their environment by attaching to surfaces and establishing mixed-species communities. As each bacterial cell attaches, it forms a new surface to which other cells can adhere. Adherence and community development are spatiotemporal; such order requires communication. The discovery of soluble signals, such as autoinducer-2, that may be exchanged within multispecies communities to convey information between organisms has emerged as a new research direction. Direct-contact signals, such as adhesins and receptors, that elicit changes in gene expression after cell-cell contact and biofilm growth are also an active research area. Considering that the majority of oral bacteria are organized in dense three-dimensional biofilms on teeth, confocal microscopy and fluorescently labeled probes provide valuable approaches for investigating the architecture of these organized communities in situ. Oral biofilms are readily accessible to microbiologists and are excellent model systems for studies of microbial communication. One attractive model system is a saliva-coated flowcell with oral bacterial biofilms growing on saliva as the sole nutrient source; an intergeneric mutualism is discussed. Several oral bacterial species are amenable to genetic manipulation for molecular characterization of communication both among bacteria and between bacteria and the host. A successful search for genes critical for mixed-species community organization will be accomplished only when it is conducted with mixed-species communities.

Bacterial coaggregation: an integral process in the development of multi-species biofilms

Coaggregation is a process by which genetically distinct bacteria become attached to one another via specific molecules. Cumulative evidence suggests that such adhesion influences the development of complex multi-species biofilms. Once thought to occur exclusively between dental plaque bacteria, there are increasing reports of coaggregation between bacteria from other biofilm communities in several diverse habitats. A general role for coaggregation in the formation of multi-species biofilms is discussed.

Modulation of Pseudomonas aeruginosa gene expression by host microflora through interspecies communication

The change in gene expression patterns in response to host environments is a prerequisite for bacterial infection. Bacterial diseases often occur as an outcome of the complex interactions between pathogens and the host. The indigenous, usually non-pathogenic microflora is a ubiquitous constituent of the host. In order to understand the interactions between pathogens and the resident microflora and how they affect the gene expression patterns of the pathogens and contribute to bacterial diseases, the interactions between pathogenic Pseudomonas aeruginosa and avirulent oropharyngeal flora (OF) strains isolated from sputum samples of cystic fibrosis (CF) patients were investigated. Animal experiments using a rat lung infection model indicate that the presence of OF bacteria enhanced lung damage caused by P. aeruginosa. Genome-wide transcriptional analysis with a lux reporter-based promoter library demonstrated that approximately 4% of genes in the genome responded to the presence of OF strains using an in vitro system. Characterization of a subset of the regulated genes indicates that they fall into seven functional classes, and large portions of the upregulated genes are genes important for P. aeruginosa pathogenesis. Autoinducer-2 (AI-2)-mediated quorum sensing, a proposed interspecies signalling system, accounted for some, but not all, of the gene regulation. A substantial amount of AI-2 was detected directly in sputum samples from CF patients and in cultures of most non-pseudomonad bacteria isolated from the sputa. Transcriptional profiling of a set of defined P. aeruginosa virulence factor promoters revealed that OF and exogenous AI-2 could upregulate overlapping subsets of these genes. These results suggest important contributions of the host microflora to P. aeruginosa infection by modulating gene expression via interspecies communications.

Prevention and elimination of upper respiratory colonization of mice by group A streptococci by using a bacteriophage lytic enzyme

Bacteriophage lytic enzymes quickly destroy the cell wall of the host bacterium to release progeny phage. Because such lytic enzymes specifically kill the species in which they were produced, they may represent an effective way to control pathogenic bacteria without disturbing normal microflora. In this report, we studied a murein hydrolase from the streptococcal bacteriophage C(1) termed lysin. This enzyme is specific for groups A, C, and E streptococci, with little or no activity toward several oral streptococci or other commensal organisms tested. Using purified lysin in vitro, we show that 1,000 units (10 ng) of enzyme is sufficient to sterilize a culture of approximately 10(7) group A streptococci within 5 seconds. When a single dose of lysin (250 units) is first added to the oral cavity of mice, followed by 10(7) live group A streptococci, it provides protection from colonization (28.5% infected, n = 21) compared with controls without lysin (70.5% infected, n = 17) (P < 0.03). Furthermore, when lysin (500 units) was given orally to 9 heavily colonized mice, no detectable streptococci were observed 2 h after lysin treatment. In all, these studies show that lysin represents a unique murein hydrolase that has a rapid lethal effect both in vitro and in vivo on group A streptococci, without affecting other indigenous microorganisms analyzed. This general approach may be used to either eliminate or reduce streptococci from the upper respiratory mucosal epithelium of either carriers or infected individuals, thus reducing associated disease.

The formation of hydrogen sulfide and methyl mercaptan by oral bacteria

The capacity to form volatile sulfur compounds was tested in bacteria isolated from subgingival microbiotas and in a representative number of reference strains. A majority of the 75 tested oral bacterial species and 7 unnamed bacterial taxa formed significant amounts of hydrogen sulfide from L-cysteine. The most active bacteria were found in the genera Peptostreptococcus, Eubacterium, Selenomonas, Centipeda, Bacteroides and Fusobacterium. Methyl mercaptan from L-methionine was formed by some members of the genera Fusobacterium, Bacteroides, Porphyromonas and Eubacterium. When incubated in serum for 7 d, the most potent producers of hydrogen sulfide were Treponema denticola and the black-pigmented species, Bacteroides intermedius, Bacteroides loescheii, Porphyromonas endodontalis and Porphyromonas gingivalis. P. endodontalis and P. gingivalis also produced significant amounts of methyl mercaptan in serum. No other volatile sulfur compound was detected in serum or in the presence of L-cysteine and L-methionine. These findings significantly increase the list of oral bacteria known to produce volatile sulfur compounds.

Antiphagocytic activity of streptococcal M protein: selective binding of complement control protein factor H

Isolated complement components were used to study the regulation of the alternative complement pathway C3 convertase (EC 3.4.21.47), also called C3b,Bb, on M protein-carrying (M+) and M protein-lacking (M-) streptococci. Neither M- nor M+ streptococci directly affected the formation or dissociation of the surface-bound C3b,Bb or the inactivation of surface-bound C3b by factor I. However, the activity of the serum control protein of the alternative complement pathway, factor H, in controlling streptococcus-bound C3b and C3b,Bb was 6-8 times stronger on M+ organisms than on M- organisms. Furthermore, M+ streptococci of different serotypes and purified streptococcal M6 protein were shown to selectively bind factor H, the dissociation constants ranging from 4.5 X 10(-6) M to 6 X 10(-7) M. We conclude that the antiphagocytic activity of streptococcal M protein may be due to complement inhibition mediated by the binding of factor H. Binding of a regulatory protein appears to be a previously unrecognized route by which a pathogen is able to evade alternative pathway activation.

Antioxidative ability of lactic acid bacteria

Nineteen strains of lactic acid bacteria were investigated for antioxidative activity. These includedLactobacillus acidophilus B, E, N1, 4356, LA-1, and Farr; Lactobacillus bulgaricus 12 278, 448, 449, Lb, 1006, and 11 842; Streptococcus thermophilus 821, MC, 573, 3641, and 19 987; and Bifidobacterium longum B6 and 15 708. Intracellular cell-free extract of all strains demonstrated antioxidative activity with inhibition rates of ascorbate autoxidation in the range of 7-12%. Antioxidative mechanisms including metal ion chelating ability, scavenge of reactive oxygen species, enzyme inhibition, and reducing activity of intracellular cell-free extract of lactic acid bacteria were studied. S. thermophilus 821 had the highest metal ion chelating ability for Fe(2+), and B. longum 15 708 showed the highest Cu(2+) chelating ability among the 19 strains tested. All strains demonstrated reactive oxygen species scavenging ability. L. acidophilus E showed the highest hydroxyl radical scavenging ability, and B. longum B6 had the best hydrogen peroxide scavenging ability. Reducing activity was also found in all strains. Most of the strains tested demonstrated excellent reducing activity. B. longum B6 showed the highest reducing activity among the 19 strains tested. In enzyme inhibition, superoxide dismutase activity was not found in these 19 strains, and the activity of superoxide dismutase was not induced when metal ion Mn(2+), Fe(2+), or Cu(2+)Zn(2+) was present.

LuxS-based signaling in Streptococcus gordonii: autoinducer 2 controls carbohydrate metabolism and biofilm formation with Porphyromonas gingivalis

Communication based on autoinducer 2 (AI-2) is widespread among gram-negative and gram-positive bacteria, and the AI-2 pathway can control the expression of genes involved in a variety of metabolic pathways and pathogenic mechanisms. In the present study, we identified luxS, a gene responsible for the synthesis of AI-2, in Streptococcus gordonii, a major component of the dental plaque biofilm. S. gordonii conditioned medium induced bioluminescence in an AI-2 reporter strain of Vibrio harveyi. An isogenic mutant of S. gordonii, generated by insertional inactivation of the luxS gene, was unaffected in growth and in its ability to form biofilms on polystyrene surfaces. In contrast, the mutant strain failed to induce bioluminescence in V. harveyi and was unable to form a mixed species biofilm with a LuxS-null strain of the periodontal pathogen Porphyromonas gingivalis. Complementation of the luxS mutation in S. gordonii restored normal biofilm formation with the luxS-deficient P. gingivalis. Differential display PCR demonstrated that the inactivation of S. gordonii luxS downregulated the expression of a number of genes, including gtfG, encoding glucosyltransferase; fruA, encoding extracellular exo-beta-D-fructosidase; and lacD encoding tagatose 1,6-diphosphate aldolase. However, S. gordonii cell surface expression of SspA and SspB proteins, previously implicated in mediating adhesion between S. gordonii and P. gingivalis, was unaffected by inactivation of luxS. The results suggest that S. gordonii produces an AI-2-like signaling molecule that regulates aspects of carbohydrate metabolism in the organism. Furthermore, LuxS-dependent intercellular communication is essential for biofilm formation between nongrowing cells of P. gingivalis and S. gordonii.

Acid tolerance, proton permeabilities, and membrane ATPases of oral streptococci

Differences in acid tolerance among representative oral streptococci were found to be related more closely to the dynamic permeabilities of the bacteria to protons than to differences in the sensitivities of cell membranes to gross damage caused by environmental acidification. For Streptococcus mutans GS-5, Streptococcus sanguis NCTC 10904, and Streptococcus salivarius ATCC 13419, gross membrane damage, indicated by the release of magnesium from whole cells, occurred at pH values below about 4 and was rapid and extensive at pH values of about 3 or less. A more aciduric, lactic acid bacterium, Lactobacillus casei ATCC 4646, was more resistant to environmental acidification, and gross membrane damage was evident only at pH values below 3. Assessments of the movements of protons into S. mutans cells after an acid pulse at various pH values indicated that permeability to protons was minimal at a pH value of about 5, at which the average half time for pH equilibration across the cell membrane was about 12 min. The corresponding values for the less aciduric organism S. sanguis were pH 7 and 8.2 min, and the values for the intermediate organism S. salivarius were pH 6 and 6.6 min. The ATPase inhibitor dicyclohexylcarbodiimide acted to increase markedly the permeability of each organism to protons, and this action indicated that permeability involved not only the passive inflow of protons but also active outflow through the proton-translocating membrane ATPase. Membranes were isolated from each of the bacteria, and pH profiles for ATPase activities indicated pH optima of about 7.5, 7.0, 6.0, and 5.0 for S. sanguis, S. salivarius, S. mutans, and L. casei, respectively. Thus, the pH profiles for the enzymes reflected the acid tolerances of the bacteria and the permeabilities of whole cells to protons.

Bacterial proteins binding to the mammalian extracellular matrix

Pathogenic bacteria frequently express surface proteins with affinity for components of the mammalian extracellular matrix, i.e. collagens, laminin, fibronectin or proteoglycans. This review summarizes our current knowledge on the mechanisms of bacterial adherence to extracellular matrices and on the biological significance of these interactions. The best-characterized bacterial proteins active in these interactions are the mycobacterial fibronectin-binding proteins, the fibronectin- and the collagen-binding proteins of staphylococci and streptococci, specific enterobacterial fimbrial types, as well as the polymeric surface proteins YadA of yersinias and the A-protein of Aeromonas. Some of these bacterial proteins are highly specific for an extracellular matrix protein, some are multifunctional and express binding activities towards a number of target proteins. The interactions can be based on a protein-protein or on a protein-carbohydrate interaction, or on a bridging mechanism mediated by a bivalent soluble target protein. Many of the interactions have also been demonstrated on tissue sections or in vivo, and adherence to the extracellular matrix has been shown to promote bacterial colonization of damaged tissues.

Comparative genomics of bacterial zinc regulons: enhanced ion transport, pathogenesis, and rearrangement of ribosomal proteins

Zinc is an important component of many proteins, but in large concentrations it is poisonous to the cell. Thus its transport is regulated by zinc repressors ZUR of proteobacteria and Gram-positive bacteria from the Bacillus group and AdcR of bacteria from the Streptococcus group. Comparative computational analysis allowed us to identify binding signals of ZUR repressors GAAATGTTATANTATAACATTTC for gamma-proteobacteria, GTAATGTAATAACATTAC for the Agrobacterium group, GATATGTTATAACATATC for the Rhododoccus group, TAAATCGTAATNATTACGATTTA for Gram-positive bacteria, and TTAACYRGTTAA of the streptococcal AdcR repressor. In addition to known transporters and their paralogs, zinc regulons were predicted to contain a candidate component of the ATP binding cassette, zinT (b1995 in Escherichia coli and yrpE in Bacillus subtilis). Candidate AdcR-binding sites were identified upstream of genes encoding pneumococcal histidine triad (PHT) proteins from a number of pathogenic streptococci. Protein functional analysis of this family suggests that PHT proteins are involved in the invasion process. Finally, repression by zinc was predicted for genes encoding a variety of paralogs of ribosomal proteins. The original copies of all these proteins contain zinc-ribbon motifs and thus likely bind zinc, whereas these motifs are destroyed in zinc-regulated paralogs. We suggest that the induction of these paralogs in conditions of zinc starvation leads to their incorporation in a fraction of ribosomes instead of the original ribosomal proteins; the latter are then degraded with subsequent release of some zinc for the utilization by other proteins. Thus we predict a mechanism for maintaining zinc availability for essential enzymes.

Secondary and tertiary structures of hyaluronan in aqueous solution, investigated by rotary shadowing-electron microscopy and computer simulation. Hyaluronan is a very efficient network-forming polymer

1. Hyaluronan from mesothelioma fluid, rooster comb and streptococci was examined by rotary shadowing and electron microscopy. All preparations showed extensive branched networks, but high-viscosity hyaluronan networks were essentially infinite, with no individual 'molecules' that were not integrated via multiple branched points into the meshwork. Low-viscosity hyaluronan, recovered after papain digestion of mesothelioma fluid, showed occasional single filaments that were independent of the main aggregates, some of which were themselves independent of other aggregates. 2. Hyaluronan is a polymer with a very marked capability to form meshworks at very low dilution (less than 1 microgram/ml). The longer the hyaluronan molecule, the more branching is potentially possible, and the more extensive and coherent is the network, with every hyaluronan molecule in contact with every other in the solution, via the network. This behaviour accounts for the mechanical properties of the soft tissues (e.g. vitreous humour) and fluids (e.g. synovial fluid) of which hyaluronan is a major component. 3. The hyaluronan twofold helix, previously demonstrated to be present in solution [Heatley & Scott (1988) Biochem. J. 254, 489-493] was shown by computer simulation and energy calculations to be sterically capable of extensive duplex formation, probably driven by interactions between the large hydrophobic patches on alternate sides of the tape-like polymer, forming stable aggregates at biological temperatures in water. This 'stickiness' is postulated to be the basis of the network-forming and laterally aggregating behaviour of hyaluronan. 4. The tertiary structures formed by hyaluronan may not be possible in the case of chondroitin 4-sulphate.

The neuropathic diabetic foot ulcer microbiome is associated with clinical factors

Nonhealing diabetic foot ulcers (DFUs) are a common and costly complication of diabetes. Microbial burden, or "bioburden," is believed to underlie delayed healing, although little is known of those clinical factors that may influence microbial load, diversity, and/or pathogenicity. We profiled the microbiomes of neuropathic nonischemic DFUs without clinical evidence of infection in 52 individuals using high-throughput sequencing of the bacterial 16S ribosomal RNA gene. Comparatively, wound cultures, the standard diagnostic in the clinic, vastly underrepresent microbial load, microbial diversity, and the presence of potential pathogens. DFU microbiomes were heterogeneous, even in our tightly restricted study population, but partitioned into three clusters distinguished primarily by dominant bacteria and diversity. Ulcer depth was associated with ulcer cluster, positively correlated with abundance of anaerobic bacteria, and negatively correlated with abundance of Staphylococcus. Ulcer duration was positively correlated with bacterial diversity, species richness, and relative abundance of Proteobacteria, but was negatively correlated with relative abundance of Staphylococcus. Finally, poor glycemic control was associated with ulcer cluster, with poorest median glycemic control concentrating to Staphylococcus-rich and Streptococcus-rich ulcer clusters. Analyses of microbial community membership and structure may provide the most useful metrics in prospective studies to delineate problematic bioburden from benign colonization that can then be used to drive clinical treatment.

Manganese transport and the role of manganese in virulence

Two areas of research have recently converged to highlight important roles for Mn(2+) in pathogenesis: the recognition that both bacterial Nramp homologs and members of LraI family of proteins are Mn(2+) transporters. Their mutation is associated with decreased virulence of various bacterial species. Thus, Mn(2+) appears to be essential for bacterial virulence. This review describes what is currently known about Mn(2+) transport in prokaryotes and how prokaryotic Mn(2+) transport is regulated. Some of the phenotypes that arise when microorganisms lack Mn(2+) are then discussed, with an emphasis on those phenotypes involving pathogenesis. The concluding section describes possible enzymatic roles for Mn(2+) that might help explain why Mn(2+) is necessary for virulence.

Adaptation of Streptococcus mutans and Enterococcus hirae to acid stress in continuous culture

Streptococcus mutans GS-5 and IB1600 adapted to growth in acidic environments in continuous culture at slow (generation time = 8.3 h) or fast (generation time = 2.4 h) rates of growth in complex medium with a restricted glucose supply. The extent of adaptation was indicated by changes in minimum pH values attained by harvested cells suspended in dense suspensions with excess glucose and by increased levels of ATPase activity assayed in permeabilized cells. Also, adapted cells better withstood potentially lethal acidification. Cells harvested from cultures growing at pH values close to 5 reduced suspension pH to lower values than cells from cultures maintained at pH 7. Cells from pH 6 cultures were intermediate. The IB1600 strain had a higher level of constitutive acid resistance than the GS-5 strain and also was better able to adapt to growth in acidified media. Both had less adaptive capacity than Enterococcus hirae ATCC 9790. Adaptation occurred rapidly, mainly within a single generation in continuous culture, while deadaptation occurred more slowly over multiple generations. The capacity of S. mutans to adapt to acid conditions is likely to be important in the ecology of dental plaque and also for the cariogenicity of the organism.

Flexible community structure correlates with stable community function in methanogenic bioreactor communities perturbed by glucose

Methanogenic bioreactor communities were used as model ecosystems to evaluate the relationship between functional stability and community structure. Replicated methanogenic bioreactor communities with two different community structures were established. The effect of a substrate loading shock on population dynamics in each microbial community was examined by using morphological analysis, small-subunit (SSU) rRNA oligonucleotide probes, amplified ribosomal DNA (rDNA) restriction analysis (ARDRA), and partial sequencing of SSU rDNA clones. One set of replicated communities, designated the high-spirochete (HS) set, was characterized by good replicability, a high proportion of spiral and short thin rod morphotypes, a dominance of spirochete-related SSU rDNA genes, and a high percentage of Methanosarcina-related SSU rRNA. The second set of communities, designated the low-spirochete (LS) set, was characterized by incomplete replicability, higher morphotype diversity dominated by cocci, a predominance of Streptococcus-related and deeply branching Spirochaetales-related SSU rDNA genes, and a high percentage of Methanosaeta-related SSU rRNA. In the HS communities, glucose perturbation caused a dramatic shift in the relative abundance of fermentative bacteria, with temporary displacement of spirochete-related ribotypes by Eubacterium-related ribotypes, followed by a return to the preperturbation community structure. The LS communities were less perturbed, with Streptococcus-related organisms remaining prevalent after the glucose shock, although changes in the relative abundance of minor members were detected by morphotype analysis. A companion paper demonstrates that the more stable LS communities were less functionally stable than the HS communities (S. A. Hashsham, A. S. Fernandez, S. L. Dollhopf, F. B. Dazzo, R. F. Hickey, J. M. Tiedje, and C. S. Criddle, Appl. Environ. Microbiol. 66:4050-4057, 2000).

Lactic acid bacteria secrete metabolites retaining anti-inflammatory properties after intestinal transport

BACKGROUND

Probiotic bacteria have a beneficial effect on intestinal inflammation. In this study, we have examined the effect of lactic acid and commensal Gram positive (+) bacteria conditioned media (CM) on tumour necrosis factor alpha (TNF-alpha) release and the mechanisms involved.

METHODS

Lipopolysaccharide (LPS) induced TNF-alpha secretion by peripheral blood mononuclear cells or the THP-1 cell line was monitored in the presence or absence of bacteria CM obtained from two probiotic strains, Bifidobacterium breve (Bb) and Streptococcus thermophilus (St), and three commensal bacterial strains (Bifidobacterium bifidum, Ruminococcus gnavus, and unidentified Streptococcus). Bb and St bacteria CM were allowed to cross filter grown intestinal epithelial cell monolayers (HT29-19A) to assess intestinal transport of active bacterial products. These products were characterised and their effect on LPS binding to THP-1 cells and nuclear factor kappa B (NF kappa B) activation assessed.

RESULTS

Dose dependent inhibition of LPS induced TNF-alpha secretion was noted for both probiotic bacteria CM (64% and 71% inhibition for Bb and St, respectively) and to a lesser extent commensal bacteria CM (21-32% inhibition). Active products from Bb and St were resistant to digestive enzymes and had a molecular mass <3000 Da. Their inhibitory effect was preserved after transepithelial transport across intestinal cell monolayers, mainly in inflammatory conditions. LPS-FITC binding to THP-1 cells and NF kappa B activation were significantly inhibited by Bb and St CM.

CONCLUSION

B breve and S thermophilus release metabolites exerting an anti-TNF-alpha effect capable of crossing the intestinal barrier. Commensal bacteria also display a TNF-alpha inhibitory capacity but to a lesser extent. These results underline the beneficial effect of commensal bacteria in intestinal homeostasis and may explain the role of some probiotic bacteria in alleviating digestive inflammation.

Relation of growth of Streptococcus lactis and Streptococcus cremoris to amino acid transport

The maximum specific growth rate of Streptococcus lactis and Streptococcus cremoris on synthetic medium containing glutamate but no glutamine decreases rapidly above pH 7. Growth of these organisms is extended to pH values in excess of 8 in the presence of glutamine. These results can be explained by the kinetic properties of glutamate and glutamine transport (B. Poolman, E. J. Smid, and W. N. Konings, J. Bacteriol. 169:2755-2761, 1987). At alkaline pH the rate of growth in the absence of glutamine is limited by the capacity to accumulate glutamate due to the decreased availability of glutamic acid, the transported species of the glutamate-glutamine transport system. Kinetic analysis of leucine and valine transport shows that the maximal rate of uptake of these amino acids by the branched-chain amino acid transport system is 10 times higher in S. lactis cells grown on synthetic medium containing amino acids than in cells grown in complex broth. For cells grown on synthetic medium, the maximal rate of transport exceeds by about 5 times the requirements at maximum specific growth rates for leucine, isoleucine, and valine (on the basis of the amino acid composition of the cell). The maximal rate of phenylalanine uptake by the aromatic amino acid transport system is in small excess of the requirement for this amino acid at maximum specific growth rates. Analysis of the internal amino acid pools of chemostat-grown cells indicates that passive influx of (some) aromatic amino acids may contribute to the net uptake at high dilution rates.

Coaggregation-mediated interactions of streptococci and actinomyces detected in initial human dental plaque

Streptococci and actinomyces that initiate colonization of the tooth surface frequently coaggregate with each other as well as with other oral bacteria. These observations have led to the hypothesis that interbacterial adhesion influences spatiotemporal development of plaque. To assess the role of such interactions in oral biofilm formation in vivo, antibodies directed against bacterial surface components that mediate coaggregation interactions were used as direct immunofluorescent probes in conjunction with laser confocal microscopy to determine the distribution and spatial arrangement of bacteria within intact human plaque formed on retrievable enamel chips. In intrageneric coaggregation, streptococci such as Streptococcus gordonii DL1 recognize receptor polysaccharides (RPS) borne on other streptococci such as Streptococcus oralis 34. To define potentially interactive subsets of streptococci in the developing plaque, an antibody against RPS (anti-RPS) was used together with an antibody against S. gordonii DL1 (anti-DL1). These antibodies reacted primarily with single cells in 4-h-old plaque and with mixed-species microcolonies in 8-h-old plaque. Anti-RPS-reactive bacteria frequently formed microcolonies with anti-DL1-reactive bacteria and with other bacteria distinguished by general nucleic acid stains. In intergeneric coaggregation between streptococci and actinomyces, type 2 fimbriae of actinomyces recognize RPS on the streptococci. Cells reactive with antibody against type 2 fimbriae of Actinomyces naeslundii T14V (anti-type-2) were much less frequent than either subset of streptococci. However, bacteria reactive with anti-type-2 were seen in intimate association with anti-RPS-reactive cells. These results are the first direct demonstration of coaggregation-mediated interactions during initial plaque accumulation in vivo. Further, these results demonstrate the spatiotemporal development and prevalence of mixed-species communities in early dental plaque.

Binding of bacterial peptidoglycan to CD14

The hypothesis that soluble peptidoglycan (sPGN, a macrophage-activator from Gram-positive bacteria) binds to CD14 (a lipopolysaccharide (LPS) receptor) was tested. sPGN specifically bound to CD14 in the following three assays: binding of soluble 32P-CD14 (sCD14) to agarose-immobilized sPGN, enzyme-linked immunosorbent assay, and photoaffinity cross-linking. sCD14 also specifically bound to agarose-immobilized muramyl dipeptide or GlcNAc-muramyl dipeptide but not to PGN pentapeptide. Binding of sCD14 to both sPGN and ReLPS (where ReLPS is LPS from Salmonella minnesota Re 595) was competitively inhibited by unlabeled sCD14, 1-152 N-terminal fragment of sCD14, sPGN, smooth LPS, ReLPS, lipid A, and lipoteichoic acid but not by dextran, dextran sulfate, heparin, ribitol teichoic acid, or soluble low molecular weight PGN fragments. Binding of sCD14 to sPGN was slower than to ReLPS but of higher affinity (KD = 25 nM versus 41 nM). LPS-binding protein (LBP) increased the binding of sCD14 to sPGN by adding another lower affinity KD and another higher Bmax, but for ReLPS, LBP increased the affinity of binding by yielding two KD with significantly higher affinity (7.1 and 27 nM). LBP also enhanced inhibition of sCD14 binding by LPS, ReLPS, and lipid A. Binding of sCD14 to both sPGN and ReLPS was inhibited by anti-CD14 MEM-18 mAb, but other anti-CD14 mAbs showed differential inhibition, suggesting conformational binding sites on CD14 for sPGN and LPS, that are partially identical and partially different.

Role of fibronectin-binding MSCRAMMs in bacterial adherence and entry into mammalian cells

Most bacterial infections are initiated by the adherence of microorganisms to host tissues. This process involves the interaction of specific bacterial surface structures, called adhesins, with host components. In this review, we discuss a group of microbial adhesins known as Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) which recognize and bind FN. The interaction of bacteria with FN is believed to contribute significantly to the virulence of a number of microorganisms, including staphylococci and streptococci. Several FN-binding MSCRAMMs of staphylococci and streptococci exhibit a similar structural organization and mechanism of ligand recognition. The ligand-binding domain consists of tandem repeats of a approximately 45 amino acid long unit which bind to the 29-kDa N-terminal region of FN. The binding mechanism is unusual in that the repeat units are unstructured and appear to undergo a conformational change upon ligand binding. Apart from supporting bacterial adherence, FN is also involved in bacterial entry into non-phagocytic mammalian cells. A sandwich model has been proposed in which FN forms a molecular bridge between MSCRAMMs on the bacterial surface and integrins on the host cell. However, the precise mechanism of bacterial invasion and the roles of FN and integrins in this process have yet to be fully elucidated.