Ultrastructure of the attachment device between coccal and filamentous microorganisms in "corn cob" formations of dental plaque

Corncob structures in dental plaque reveal microhabitat taxon specificity

BACKGROUND

The human mouth is a natural laboratory for studying how bacterial communities differ across habitats. Different bacteria colonize different surfaces in the mouth-teeth, tongue dorsum, and keratinized and non-keratinized epithelia-despite the short physical distance between these habitats and their connection through saliva. We sought to determine whether more tightly defined microhabitats might have more tightly defined sets of resident bacteria. A microhabitat may be characterized, for example, as the space adjacent to a particular species of bacterium. Corncob structures of dental plaque, consisting of coccoid bacteria bound to filaments of Corynebacterium cells, present an opportunity to analyze the community structure of one such well-defined microhabitat within a complex natural biofilm. Here, we investigate by fluorescence in situ hybridization and spectral imaging the composition of the cocci decorating the filaments.

RESULTS

The range of taxa observed in corncobs was limited to a small subset of the taxa present in dental plaque. Among four major groups of dental plaque streptococci, two were the major constituents of corncobs, including one that was the most abundant Streptococcus species in corncobs despite being relatively rare in dental plaque overall. Images showed both Streptococcus types in corncobs in all individual donors, suggesting that the taxa have different ecological roles or that mechanisms exist for stabilizing the persistence of functionally redundant taxa in the population. Direct taxon-taxon interactions were observed not only between the Streptococcus cells and the central corncob filament but also between Streptococcus cells and the limited subset of other plaque bacteria detected in the corncobs, indicating species ensembles involving these taxa as well.

CONCLUSIONS

The spatial organization we observed in corncobs suggests that each of the microbial participants can interact with multiple, albeit limited, potential partners, a feature that may encourage the long-term stability of the community. Additionally, our results suggest the general principle that a precisely defined microhabitat will be inhabited by a small and well-defined set of microbial taxa. Thus, our results are important for understanding the structure and organizing principles of natural biofilms and lay the groundwork for future work to modulate and control biofilms for human health. Video Abstract.

Ancient dental calculus preserves signatures of biofilm succession and interindividual variation independent of dental pathology

Dental calculus preserves oral microbes, enabling comparative studies of the oral microbiome and health through time. However, small sample sizes and limited dental health metadata have hindered health-focused investigations to date. Here, we investigate the relationship between tobacco pipe smoking and dental calculus microbiomes. Dental calculus from 75 individuals from the 19th century Middenbeemster skeletal collection (Netherlands) were analyzed by metagenomics. Demographic and dental health parameters were systematically recorded, including the presence/number of pipe notches. Comparative data sets from European populations before and after the introduction of tobacco were also analyzed. Calculus species profiles were compared with oral pathology to examine associations between microbiome community, smoking behavior, and oral health status. The Middenbeemster individuals exhibited relatively poor oral health, with a high prevalence of periodontal disease, caries, heavy calculus deposits, and antemortem tooth loss. No associations between pipe notches and dental pathologies, or microbial species composition, were found. Calculus samples before and after the introduction of tobacco showed highly similar species profiles. Observed interindividual microbiome differences were consistent with previously described variation in human populations from the Upper Paleolithic to the present. Dental calculus may not preserve microbial indicators of health and disease status as distinctly as dental plaque.

Corynebacterium matruchotii: A Confirmed Calcifying Bacterium With a Potentially Important Role in the Supragingival Plaque

Corynebacterium matruchotii is a reported calcifying bacterium that can usually be isolated from dental calculus and induce mineralization in vitro. In recent years, based on in situ hybridization probe and sequencing technology, researchers have discovered the central "pillar" role of C. matruchotii in supragingival plaque, and many studies focused on bacterial interactions in the biofilm structure dominated by C. matruchotii have been conducted. Besides, C. matruchotii seems to be an indicator of "caries-free" oral status according to imaging and sequencing studies. Therefore, in this review, we summarize C. matruchotii 's role in supragingival plaque based on the structure, interactions, and potential connections with oral diseases.

Actinomycosis as a Rare Local Manifestation of Severe Periodontitis

Actinomycosis is a chronic suppurative infection primarily caused by anaerobic gram-positive filamentous bacteria, primarily of the genus Actinomyces. Oral-cervicofacial actinomycosis is the localization found most often, presenting as a soft tissue swelling, an abscess, a mass lesion, or sometimes an ulcerative lesion. Periodontitis-like lesions, however, are rare findings. This report describes the case of a 41-year-old healthy female patient (nonsmoker), who was referred to the clinic with dull and throbbing pain in the second quadrant. Tooth 25 showed increased mobility and probing pocket depths up to 10 mm, with profuse bleeding upon probing. Radiographically, considerable interproximal horizontal bone loss was found, and the diagnosis of periodontitis stage 3, grade C was made. The situation was initially stabilized with adhesive splinting and local anti-infective therapy. Two weeks later, the bone defect was treated with guided tissue regeneration (GTR) using a xenogenic filler material (BioOss Collagen) and a resorbable membrane (Bio-Gide). Due to a suspicious appearance of the excised granulation tissue, the collected fragments were sent for histopathological evaluation. This evaluation revealed a chronic granulomatous inflammation with the presence of filamentous bacterial colonies, consistent with Actinomyces. The patient was successfully treated. While there are only few reports in the literature, actinomycotic lesions represent a rare but possible finding in cases with localized periodontal destruction. In conclusion, systematic biopsy of the infrabony tissue in localized periodontal lesions may help to provide a more accurate counting of Actinomyces-associated lesions, thereby improving diagnosis, therapy, and prevention.

Measuring the subgingival microbiota in periodontitis patients: Comparison of the surface layer and the underlying layers

Periodontitis is a major cause of tooth loss in adults that initially results from dental plaque. Subgingival plaque pathogenesis is affected by both community composition and plaque structures, although limited data are available concerning the latter. To bridge this knowledge gap, subgingival plaques were obtained using filter paper (the fourth layer) and curette (the first-third layers) sequentially and the phylogenetic differences between the first-third layers and the fourth layer were characterized by sequencing the V3-V4 regions of 16S rRNA. A total of 11 phyla, 148 genera, and 308 species were obtained by bioinformatic analysis, and no significant differences between the operational taxonomic unit numbers were observed for these groups. In both groups, the most abundant species were Porphyromonas gingivalis and Fusobacterium nucleatum. Actinomyces naeslundii, Streptococcus intermedius, and Prevotella intermedia possessed relatively high proportions in the first-third layers; while in the fourth layer, both traditional pathogens (Treponema denticola and Campylobacter rectus) and novel pathobionts (Eubacterium saphenum, Filifactor alocis, Treponema sp. HOT238) were prominent. Network analysis showed that either of them exhibited a scale-free property and was constructed by two negatively correlated components (the pathogen component and the nonpathogen component), while the synergy in the nonpathogen component was lower in the first-third layers than that in the fourth layer. After merging these two parts into a whole plaque group, the negative/positive correlation ratio increased. With potential connections, the first-third layers and the fourth layer showed characteristic key nodes in bacterial networks.

Biogeography of the Oral Microbiome: The Site-Specialist Hypothesis

Microbial communities are complex and dynamic, composed of hundreds of taxa interacting across multiple spatial scales. Advances in sequencing and imaging technology have led to great strides in understanding both the composition and the spatial organization of these complex communities. In the human mouth, sequencing results indicate that distinct sites host microbial communities that not only are distinguishable but to a meaningful degree are composed of entirely different microbes. Imaging suggests that the spatial organization of these communities is also distinct. Together, the literature supports the idea that most oral microbes are site specialists. A clear understanding of microbiota structure at different sites in the mouth enables mechanistic studies, informs the generation of hypotheses, and strengthens the position of oral microbiology as a model system for microbial ecology in general.

Co-localized or randomly distributed? Pair cross correlation of in vivo grown subgingival biofilm bacteria quantified by digital image analysis

The polymicrobial nature of periodontal diseases is reflected by the diversity of phylotypes detected in subgingival plaque and the finding that consortia of suspected pathogens rather than single species are associated with disease development. A number of these microorganisms have been demonstrated in vitro to interact and enhance biofilm integration, survival or even pathogenic features. To examine the in vivo relevance of these proposed interactions, we extended the spatial arrangement analysis tool of the software daime (digital image analysis in microbial ecology). This modification enabled the quantitative analysis of microbial co-localization in images of subgingival biofilm species, where the biomass was confined to fractions of the whole-image area, a situation common for medical samples. Selected representatives of the disease-associated red and orange complexes that were previously suggested to interact with each other in vitro (Tannerella forsythia with Fusobacterium nucleatum and Porphyromonas gingivalis with Prevotella intermedia) were chosen for analysis and labeled with specific fluorescent probes via fluorescence in situ hybridization. Pair cross-correlation analysis of in vivo grown biofilms revealed tight clustering of F. nucleatum/periodonticum and T. forsythia at short distances (up to 6 µm) with a pronounced peak at 1.5 µm. While these results confirmed previous in vitro observations for F. nucleatum and T. forsythia, random spatial distribution was detected between P. gingivalis and P. intermedia in the in vivo samples. In conclusion, we successfully employed spatial arrangement analysis on the single cell level in clinically relevant medical samples and demonstrated the utility of this approach for the in vivo validation of in vitro observations by analyzing statistically relevant numbers of different patients. More importantly, the culture-independent nature of this approach enables similar quantitative analyses for “as-yet-uncultured” phylotypes which cannot be characterized in vitro.

Efficacy of removal of sucrose-supplemented interproximal plaque by electric toothbrushes in an in vitro model

Electric toothbrushes were evaluated using a model of plaque removal by fluid shear forces. Sucrose supplementation during plaque development did not affect the removal of bacteria from biofilm exposed to low-energy shear but did increase their resistance to high-energy shear. The toothbrush supplying high-energy shear forces removed significantly more viable bacteria.

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.

Determining the spatial distribution of viable and nonviable bacteria in hydrated microcosm dental plaques by viability profiling

AIMS

The aim of this study was to use confocal laser scanning microscopy (CLSM) to examine the spatial distribution of both viable and nonviable bacteria within microcosm dental plaques grown in vitro. Previous in vivo studies have reported upon the distribution of viable bacteria only.

METHODS AND RESULTS

Oral biofilms were grown on hydroxyapatite (HA) discs in a constant-depth film fermenter (CDFF) from a saliva inoculum. The biofilms were stained with the BacLight LIVE/DEAD system and examined by CLSM. Fluorescence intensity profiles through the depth of the biofilm showed an offset between the maximum viable intensity and the maximum nonviable intensity. Topographical differences between the surface properties of the viable and nonviable biofilm virtual surfaces were also measured.

CONCLUSIONS

The profile of fluorescence intensity from viable and nonviable staining suggested that the upper layers of the biofilm contain proportionally more viable bacteria than the lower regions of the biofilm.

SIGNIFICANCE AND IMPACT OF STUDY

Viability profiling records the transition from predominantly viable to nonviable bacteria through biofilms suggesting that this technique may be of use for quantifying the effects of antimicrobial compounds upon biofilms. The distribution of viable bacteria was similar to that found in dental plaque in vivo suggesting that the CDFF produces in vitro biofilms which are comparable to their in vivo counterparts in terms of the spatial distribution of viable bacteria.

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.

Oral microbial communities: biofilms, interactions, and genetic systems

Oral microbial-plaque communities are biofilms composed of numerous genetically distinct types of bacteria that live in close juxtaposition on host surfaces. These bacteria communicate through physical interactions called coaggregation and coadhesion, as well as other physiological and metabolic interactions. Streptococci and actinomyces are the major initial colonizers of the tooth surface, and the interactions between them and their substrata help establish the early biofilm community. Fusobacteria play a central role as physical bridges that mediate coaggregation of cells and as physiological bridges that promote anaerobic microenvironments which protect coaggregating strict anaerobes in an aerobic atmosphere. New technologies for investigating bacterial populations with 16S rDNA probes have uncovered previously uncultured bacteria and have offered an approach to in situ examination of the spatial arrangement of the participant cells in oral-plaque biofilms. Flow cells with saliva-coated surfaces are particularly useful for studies of biofilm formation and observation. The predicted sequential nature of colonization of the tooth surface by members of different genera can be investigated by using these new technologies and imaging the cells in situ with confocal scanning laser microscopy. Members of at least seven genera now can be subjected to genetic studies owing to the discovery of gene-transfer systems in these genera. Identification of contact-inducible genes in streptococci offers an avenue to explore bacterial responses to their environment and leads the way toward understanding communication among inhabitants of a multispecies biofilm.

Dental plaque development on defined streptococcal surfaces

Coaggregations between bacterial species have been widely studied in vitro but not in the mouth. A new in vivo assay was used to measure the rate and composition of indigenous plaque formation onto bovine enamel chips covered with a continuous layer of bacteria. Chips were covered with Streptococcus oralis ATCC 10557, which coaggregated with many oral species, or Streptococcus gordonii S7, which did not coaggregate with these oral species, and placed in the mouth for 4 and 24 h. There were no differences in the number of most indigenous bacterial species isolated from the two streptococcal surfaces. However, the number of Actinomyces viscosus as a proportion of total Actinomyces spp. was significantly different on the two surfaces at 24 h. With the exception of Actinomyces naeslundii and A. viscosus removed from the S7 surface, all indigenous species increased significantly in number from 4 to 24 h, irrespective of the streptococcal surface. This study demonstrated that interbacterial coaggregation had only a limited effect on in vivo plaque development. Thus suggesting that environmental factors, growth or other adherence phenomena are dominant in in vivo plaque formation.

The apical border plaque in chronic adult periodontitis. An ultrastructural study. I. Morphology, structure, and cell content

THIS STUDY CONCERNS THE APICAL BORDER (AB) plaque in relation to chronic adult periodontitis (AP). Fifty-six teeth from 24 patients with AP were examined by transmission electron microscopy (TEM). The AB was not discrete with islands of bacteria in the so-called plaque-free zone (PFZ). Coronal to the AB, the established plaque commonly consisted of three to four layers of Gram-positive and Gram-negative cocci, rods, filaments, and spirochetes and a superficial layer, mainly of spirochetes, but including filaments, "test tube brush," and "corn-cob" formations. The most apical apparently intact organisms in the PFZ were in bacterial islands or in isolation and were predominantly Gram-negative cocci and rods, with occasional other morphotypes. The most apical microorganisms were invariably ghost cells. A cuticle of varying thickness and structure was present at the plaque/tooth interface. It was concluded that there was a limited range of intact bacterial morphotypes in the apical border plaque in chronic periodontitis.

Inhibition of intergeneric coaggregation among oral bacteria by cetylpyridinium chloride, chlorhexidine digluconate and octenidine dihydrochloride

The potential inhibitory effect of chlorhexidine digluconate on the intergeneric coaggregation of 11 pairs of Gram-positive organisms was compared to its ability to inhibit coaggregations of 14 pairs comprised of both a Gram-positive and a Gram-negative cell type. Dramatic differences in the inhibitory effectiveness of the antimicrobial compound on the two kinds of coaggregation pairs were found. Gram-positive pairs were not inhibited at a concentration of 0.25%, whereas the coaggregations involving a Gram-negative partner were usually completely blocked at concentrations as low as 0.01%. Similar effects to chlorhexidine digluconate were found with octenidine dihydrochloride and cetylpyridinium chloride, while sodium dodecylsulfate was inhibitory only at 10- to 50-fold higher concentrations. These results suggest that chlorhexidine digluconate, octenidine dihydrochloride, and cetylpyridinium chloride may be effective inhibitors of later microbial colonizers of dental plaque but may not disturb a normal healthy indigenous flora.

Periapical bacterial plaque in teeth refractory to endodontic treatment

It has recently been found that bacteria are able to survive and maintain an infectious disease process in periapical lesions of nonvital teeth. The purpose of this study was to examine the surfaces of root tips removed during surgical-endodontic treatment for the presence of microorganisms. A full thickness flap was reflected under strict surgical asepsis and the periapical lesions were enucleated and removed. About 2-3 mm of the root was cut off, rinsed in sterile saline and placed in 10% neutral-buffered formalin. Upon fixation, the root tips were dehydrated, air-dried and given an electrically conducting coat of gold in a vacuum evaporator. The root tips were then studied in a Jeol, JSM-U3 scanning electron microscope, usually operated at 20 kV. The root surfaces were covered with soft tissue, except at the apex of the roots, where a continuous, smooth and structureless coating was seen, apparently adjacent to the apical foramen. At higher magnification a variety of bacterial forms were recognized in the smooth coating. A bacterial plaque was observed in irregularities of the surfaces between fiber bundles and cells and in crypts and holes. The bacteria were held together by an extracellular material and the plaque was dominated by cocci and rods. Fibrillar forms were recognized as well, often with cocci attached to their surfaces.

Coaggregation of Fusobacterium nucleatum, Selenomonas flueggei, Selenomonas infelix, Selenomonas noxia, and Selenomonas sputigena with strains from 11 genera of oral bacteria

Twenty-eight strains of Fusobacterium nucleatum and 41 Selenomonas strains, including S. sputigena (24 strains), S. flueggei (10 strains), S. infelix (5 strains), and S. noxia (2 strains), were tested for their ability to coaggregate with each other and with 49 other strains of oral bacteria representing Actinobacillus, Actinomyces, Bacteroides, Capnocytophaga, Gemella, Peptostreptococcus, Porphyromonas, Propionibacterium, Rothia, Streptococcus, and Veillonella species. Selenomonads coaggregated with fusobacteria and with Actinomyces naeslundii PK984 but not with any of the other bacteria, including other selenomonads. In contrast, fusobacteria coaggregated with members of all genera, although not with all strains of each species tested. Each fusobacterium strain appeared to have its own set of partners and coaggregation properties, unlike their partners, whose coaggregation properties in earlier surveys delineated distinct coaggregation groups. Coaggregations of fusobacteria with the 63 gram-negative strains were usually inhibited by EDTA, whereas those with the 27 gram-positive strains were usually not inhibited. Likewise, lactose-inhibitable coaggregations were common among some strains of fusobacteria and some strains from each of the genera containing gram-negative partners but were rarely observed with gram-positive partners. Heating the fusobacteria at 85 degrees C for 30 min completely prevented coaggregation with most partners, suggesting the involvement of a protein on the fusobacteria. Heat treatment of many of the gram-negative partners not only enhanced their coaggregation with the fusobacteria but also changed lactose-sensitive coaggregations to lactose-insensitive coaggregations. Although fusobacteria coaggregated with a broader variety of oral partner strains than any other group of oral bacteria tested to date, each fusobacterium exhibited coaggregation with only a certain set of partner strains, and none of the fusobacteria adhered to other strains of fusobacteria, indicating that recognition of partner cell surfaces is selective. The strains of F. nucleatum are heterogeneous and cannot be clustered into distinct coaggregation groups. Collectively, these results indicate that coaggregation between fusobacteria and many gram-negative partners is significantly different from their coaggregation with gram-positive partners. The contrasting variety of partners for fusobacteria and selenomonads supports the concept of coaggregation partner specificity that has been observed with every genus of oral bacteria so far examined.

Inhibition of coaggregation between Fusobacterium nucleatum and Porphyromonas (Bacteroides) gingivalis by lactose and related sugars

The coaggregation of Fusobacterium nucleatum PK1594 and Porphyromonas (Bacteroides) gingivalis PK1924 was inhibited equally well by lactose, N-acetyl-D-galactosamine, and D-galactose, which caused 50% inhibition of coaggregation at 2 mM sugar concentration. Other sugars such as D-galactosamine, D-fucose (6-deoxy-D-galactose), and alpha-methyl- and beta-methyl-D-galactosides also inhibited coaggregation. Sugar specificity was apparent, since neither L-fucose, L-rhamnose, N-acetyl-D-glucosamine, nor N-acetylneuraminic acid was an inhibitor. Protease treatment of the fusobacterium completely abolished coaggregation, whereas it had no effect on the coaggregating activity of the porphyromonad. Although numerous lactose-inhibitable coaggregating pairs are known to occur among gram-positive bacteria, this report and the accompanying survey (P. E. Kolenbrander, R. N. Andersen, and L. V. H. Moore, Infect. Immun. 57:3194-3203, 1989) are the first studies demonstrating the extensive nature of this type of interaction between gram-negative human oral bacteria. The significance of galactoside-inhibitable coaggregations between these two potential periodontal pathogens is discussed.

The establishment of reproducible, complex communities of oral bacteria in the chemostat using defined inocula

Nine commonly isolated oral bacterial populations were inoculated into a glucose-limited and a glucose-excess (amino acid-limited) chemostat maintained at a constant pH 7.0 and a mean community generation time of 13.9 h. The bacterial populations were Streptococcus mutans ATCC 2-27351, Strep. sanguis NCTC 7865, Strep. mitior EF 186, Actinomyces viscosus WVU 627, Lactobacillus casei AC 413, Neisseria sp. A1078, Veillonella alkalescens ATCC 17745, Bacteroides intermedius T 588 and Fusobacterium nucleatum NCTC 10593. All nine populations became established in the glucose-limited chemostat although Strep. sanguis and Neisseria sp. were present only after a second and third inoculation, respectively. In contrast, even following repeated inoculations, Strep. mutans, B. intermedius and Neisseria sp. could not be maintained under glucose-excess conditions. A more extensive pattern of fermentation products and amino acid catabolism occurred under glucose-limited growth; this simultaneous utilization of mixed substrates also contributed to the higher yields (Y molar glucose) and greater species diversity of these communities. Microscopic and biochemical evidence suggested that cell-to-cell interactions and food chains were occurring among community members. To compare the reproductibility of this system, communities were established on three occasions under glucose-limitation and twice under glucose-excess conditions. The bacterial composition of the steady-state communities and their metabolic behaviour were similar when grown under identical conditions but varied in a consistent manner according to the nutrient responsible for limiting growth. Although a direct simulation of the oral cavity was not attempted, the results show that the chemostat could be used as an environmentally-related model to grow complex but reproducible communities of oral bacteria for long periods from a defined inoculum.

Aggregation of enzymatically modified Streptococcus mitis indicating involvement of lectin-ligand type interaction

The aggregation properties of Streptococcus mitis ATCC 903 cells modified by treatment with heat or different enzymes was investigated. Bacteria that had the ability to aggregate spontaneously lost this capacity by treatment with proteolytic enzymes, beta-galactosidase or heat. Cells subjected to different types of modification were mixed in various proportions and their aggregation properties were recorded. To discriminate between the two kinds of cells in the suspension, one partner in the aggregation reaction was labelled with 14C-palmitic acid. Bacteria treated with beta-galactosidase co-aggregated with spontaneously aggregating cells (not modified) and with cells treated with heat. Heat-treated cells co-aggregated with spontaneously aggregating cells and with cells treated with beta galactosidase. Cells treated with trypsin did not co-aggregate either with spontaneously aggregating cells or cells treated with heat or beta-galactosidase. These findings are consistent with the hypothesis that two surface components are required for specific aggregation of S. mitis cells. We suggest that both components are degraded or released from the bacterial surface by treatment with trypsin (and other proteolytic enzymes) as shown by the inability of these cells to take part in any co-aggregation with spontaneously aggregating cells. Treatment with beta-galactosidase degrades a carbohydrate receptor constituting the terminal part of a glycoprotein. Heat treatment inactivates a protein lectin. The fact that heat-treated bacteria and bacteria treated with beta-galactosidase aggregate when mixed supports the assumption that two components take part in the aggregation reaction.

Specific coaggregation and the cell wall of Streptococcus sanguis

Sacculi prepared from Streptococcus sanguis 34 by extensive extraction of cells with hot sodium dodecyl sulfate-2-mercaptoethanol retained the ability to coaggregate with Actinomyces viscosus T14V. When S. sanguis 34 was disrupted by homogenization with glass beads and fractionated by differential centrifugation, only the cell wall fraction agglutinated A. viscosus T14V. When strain 34 was treated with lysozyme, the coaggregating capability of the cells was essentially unaltered. Sacculi prepared from lysozyme-treated strain 34 and additionally purified by electrophoresis were agglutinated by strain T14V.

Corncob formation between Fusobacterium nucleatum and Streptococcus sanguis

Corncob formation in dental plaque was believed to be limited to strains of Bacterionema matruchotii and Streptococcus sanguis. We observed recently that strains of Fusobacterium nucleatum also interacted with S. sanguis to form corncobs. Since the fusobacteria are among the first anaerobic filaments to colonize subgingival plaque, these interactions could serve as a connecting link between the transformation of supra- to subgingival plaque. To further characterize these interactions, quantitative in vitro studies of the kinetics of corncob formation of the fusobacteria were undertaken. These studies indicated that fewer streptococci were needed to saturate F. nucleatum strain 364 compared to strain 10953. Corncob formation with both strains was enhanced with increasing pH up to pH 8, at which point autoaggregation of the streptococci occurred. Variation in ionic strength and divalent cations had little effect on the interaction, and EDTA suppressed aggregate formation only slightly. Detergents at concentrations above 0.05% also inhibited corncob formation. Electron micrographs suggested that attachment of the cocci to the fusiforms was mediated through localized tufts of fimbriae, as they are in the Bacterionema system. However, although both trypsin and heat treatment of the streptococci inhibited corncob formation with fusobacteria, the effects were not as complete as those seen in Bacterionema species. Unlike the Bacterionema model, trypsin and heat treatment of the fusobacteria resulted in inhibition of corncob formation. These results suggest that several different receptors may be involved in corncob formation.

Development of aggregating ability in cells of Streptococcus mitis ATCC 903 grown under glucose-limiting conditions in continuous culture

Streptococcus mitis ATCC 903 grown under glucose-limiting conditions in continuous culture did not aggregate upon incubation in 10 mM phosphate buffer at pH 5--7 unless a metabolizable sugar was added. Aggregation started 45--60 min after the addition of glucose or sucrose whereas slowly metabolized sugars as galactose and lactose required several hours to cause aggregation. Active metabolism of the carbohydrate was a prerequisite for aggregation as indicated by acid formation. Chloramphenicol inhibited the development of aggregating ability in the presence of glucose or sucrose. The addition of a source of nitrogen (peptides and amino acids) enhanced aggregation and shortened the time for development of aggregating ability. No aggregation occurred at at 0 degrees C and the ability to aggregate was markedly delayed at 20 degrees C as compared to 30 degrees C and 37 degrees C. Trypsin treatment of the bacteria abolished aggregation, indicating that surface components of protein or glycoprotein nature contributed to the capacity to aggregate.

Chemostat studies of the effect of environmental control on Streptococcus sanguis adherence to hydroxyapatite

Streptococcus sanguis is a major component of early dental plaque. The ability of S. sanguis to adhere to salivary pellicle appears to involve specific bacterial surface receptors. The nature of these receptors is still not known; however, the component molecules may be subject to environmental control as has been shown for teichoic acids and certain proteins. To study these environmental effects, a chemostat was employed to vary the growth conditions of Streptococcus sanguis strain G9B. This strain has been used extensively to study the adhesion of [(3)H]thymidine-labeled batch-grown cells to saliva-coated hydroxyapatite beads. The effects of dilution rate, pH, and carbon source on adhesion were studied with a competition assay in which the labeled batch cells were used as a reference standard. In this assay, cells from the chemostat were harvested and compared for their ability to inhibit adhesion of labeled cells relative to unlabeled control batch-grown cells. Subsequent studies used chemostat grown cells labeled with [(3)H]thymidine as a reference standard so that results were internally controlled and reflected only the particular alteration in environment which was studied. These results indicated that when glucose was used as a growth-limiting substrate, cells grown at relatively high dilution rates (D = 0.5 h(-1); mean generation time = 1.4 h) behaved similarly to batch-grown cells and appeared to compete for the same binding sites. Cells grown at D = 0.1 h(-1) (mean generation time = 7 h) no longer competed with either batch-grown cells or chemostat cells grown at D = 0.5 h(-1). Moreover, adsorption isotherms of such slow-growing cells (D = 0.1 h(-1)) suggested that binding was no longer specific. When fructose was used as the growth-limiting carbohydrate, cells grown at D = 0.1 h(-1) did not show this loss of specificity and competed nearly as well as control batch-grown glucose cells. However, the effect of pH appeared to be independent of carbohydrate source, because cells grown in either glucose or fructose at pH 5.5 at D = 0.1 h(-1) lost the ability to compete with reference batch or chemostat cells grown at D = 0.5 h(-1). This effect was very sharp, since cells grown in the pH range from 6 to 7.5 at D = 0.5 h(-1) competed nearly as well as control cells. A similar effect of pH was found for batch cultures grown with excess glucose. These studies reinforce the idea that the environment can profoundly affect the bacterial surface and consequently the ability of the organism to adhere, a property which appears to be a primary event in some infectious diseases and in dental plaque formation.

Quantitative in vitro assay for "corncob" formation

The interaction of Bacterionema matruchotii with strains of Streptococcus sanguis produces a structure which morphologically resembles a corncob. To determine the specific bacterial surface receptors involved in the interaction, we developed a quantitative assay. The assay consisted of mixing saline suspensions of [CH(3)-(3)H]thymidine-labeled streptococci and B. matruchotii, incubating at 37 degrees C for 2 h, and filtering the mixture through a 5-mum polycarbonate membrane filter. The free cocci and filaments passed through the filter, but the corncobs were retained. Estimates of the number of corncobs formed were obtained by quantitating the radioactivity retained on the membranes relative to that of controls of streptococci alone. Although saturation of the Bacterionema occurred at a ratio of streptococci to Bacterionema of 10:1 (Klett units), a 2:1 ratio was chosen because of the increased sensitivity of the assay at this ratio. The percentage of streptococci binding at this ratio was 18.6 +/- 8.1 (standard deviation). All five Bacterionema strains tested formed corncobs; in contrast, only three strains of S. sanguis were positive. These were serotype 1 strains which had localized surface "fuzz." Although scanning electron microscopic observations revealed an almost random distribution of cocci along the filament surface, transmission electron microscopy revealed that the streptococci were attached to the Bacterionema by the surface fuzz. No differences in corncob formation were observed in sodium phosphate buffer, pH 6 to 8, at phosphate concentrations ranging from 0.005 to 0.05 M. Concentrations of NaCl or KCl up to 0.25 M did not affect corncob formation, and low concentrations of CaCl(2) increased corncob formation slightly, whereas MgCl(2), ethylenediaminetetraacetic acid, and citrate buffers reduced the number of streptococci binding to the filaments. These results suggest that divalent cations may play a role in this process.

Formation of salivary coating and dental plaque on two different supporting materials. An electron microscopic study

The formation of salivary coating (SC) and dental plaque on top of Vestopal W and enamel inlays was studied with scanning and transmission electron microscopy. No clear morphological differences were found between SC and dental plaque formed on either material. A thin continuous SC was formed on the supporting material in all volunteers within 30 minutes' oral exposure. The SC appeared smooth and contained numerous protruding small round bodies (40-200 nm in size), the numbers of which increased with increasing time. Bacterial colonization of the SC started between 6 and 12 hours' oral exposure. After 24 hours' oral exposure, bacterial colonies were confluenting and partly obscuring the subjacent SC. No evidence was obtained in this study contraindicating the use of Vestopal W as supporting material for experimental plaque studies.

Morphologic studies on dental plaque formation

The present summary and the following papers (I--VII) are submitted in partial fulfillment of the requirements for the degree of Doctor Odontologiae at the University of Bergen. 1: Growth of dental plaque on hydroxyapatite splints. A method of studying early plaque morphology. J. Periodontal Res. 1974, 9, 135--146. II: Pellicle formation on hydroxyapatite splints attached to the human dentition: Morphologic confirmation of the concept of adsorption. Arch. Oral Biol. 1975, 20, 739-742. III: Scanning and transmission electron microscope study of pellicle morphogenesis. Scand. J. Dent. Res. 1977, 85, 217-231. IV: Early dental plaque morphogenesis. A scanning electron microscope study using the hydorxyapatite splint model and a low-sucrose diet. J. Periodontal Res. 1977, 12, 73-89. V: Ultrastructural study of early dental plaque formation. J. Periodontal Res. 1978, 13, 391-409. VI: Dental plaque morphology as revealed by direct observation and by replicating techniques. Acta Odontol. Scand. 1978, 36, 279-288 Co-author: F. Gusberti. VII: Replica study of plaque formation on human tooth surfaces. Acta Odontol. Scand. 1979, 37, 65-72. Co-author: F. Gusberti. These papers are referred to as I-VII in the present summary. Other papers are referred to in conventional manner.

Antigens of Streptococcus sanguis: purification and characterization of the b antigen

The antigen defining Streptococcus sanguis serotype 2 has been designated the b antigen. This antigen can be detected in extracts, obtained from whole cells by autoclaving (Rantz and Randall extraction), as a single precipitin band using a reference antiserum (M-5). However, the extract can also be shown to contain a teichoic acid using anti-polyglycerol phosphate serum. This teichoic acid does not contain the antigenic determinant for group H specificity. Studies of the b antigen have been hampered because of the difficulty in separating the b antigen from the teichoic acid using ion-exchange and molecular sieve chromatography. However, a relatively pure preparation has been obtained by affinity chromatography using anti-polyglycerol phosphate serum coupled to Sepharose. The isolated b antigen is a typical streptococcal cell wall polysaccharide composed of glucose, rhamnose, and N-acetylglucosamine in a molar ratio of 2.5:1.0:0.1. The antigen appears to have a single antigenic determinant closely related to isomaltose (glucose alpha-1,6-glucoside) based upon hapten inhibition studies.

Dextran-mediated interbacterial aggregation between dextran-synthesizing streptococci and Actinomyces viscosus

Streptococcus sanguis and Streptococcus mutans bind to the surface of Actinomyces viscosus, producing large microbial aggregates. Aggregates form rapidly and are not easily dissociated by vigorous mixing. The binding is mediated by dextran. Glucose-grown streptococci will not aggregate unless they are first mixed with high-molecular-weight dextran. Aggregation is induced with dextrans isolated from Leuconostoc, S. sanguis, or S. mutans. Sucrose-grown streptococci will adhere to A. viscosus without the addition of an exogenous source of dextran. A. viscosus will bind dextran and then bind glucose-grown streptococci. Aggregation occurs over a wide pH range and is dependent on cations. The aggregating activity of A. viscosus is both protease and heat sensitive. The aggregating activity of S. sanguis is heat stable but sensitive to dextranase.

Structure of the microbial flora associated with periodontal health and disease in man. A light and electron microscopic study

Teeth slated for extraction were evaluated with respect to their periodontal status and classified accordingly into five categories; namely normal, gingivitis, periodontitis, periodontosis and postperiodontosis. After processing, one approximal surface of each tooth was sampled at various levels in an apico-occlusal direction for light and electron microscopic study of the associated bacterial flora. In normal samples, the flora consisted of a relatively thin, adherent bacterial layer confined to the enamel surface. The cells were predominantly coccoid in shape with cell wall features compatible with those of Gram-positive organisms. Isolated filamentous or branching forms and some Gram-negative bacteria were noted on the surface of the more apical portion of the bacterial layer. No flagellated cells or spirochetes were present. Gingivitis samples yielded a relatively more voluminous and complex supragingival flora with relatively more filamentous bacteria and more cells with a Gram-negative cell wall ultrastructure. These samples also contained corncob formations on the surface of supragingival deposits, and flagellated cells with spirochetes within the predominantly Gram-negative flora of the sulcus bottom. Supragingival bacterial deposits of periodontitis samples were similar to those observed in gingivitis. The subgingival flora consisted of relatively fewer cells adherent to the root surface with a concomitant increase in the population of Gram-negative and flagellated cells, as well as spirochetes. The tissue side of the subgingival flora generally exhibited a distinctive concentration of "test-tube brush" formations, spirochetes of predominantly medium size, and assorted cell types peculiar to this region. A transitional flora generally separated the supra- from the subgingival microbial population. Periodontosis samples had a relatively sparse, predominantly Gram-negative flora. A unique electron-dense, lobulated cuticular deposit covered the majority of the samples studied. Postperiodontosis samples were much more similar in their microbial flora to the periodontitis group. The results suggest that (1) a certain microbial flora may be compatible with a state of periodontal health; (2) a different flora is associated with varying degrees of periodontal disease; (3) the structure and composition of the supragingival flora differs markedly from that of the subgingival flora; (4) with the exception of periodontis, the alterations of the microbial flora as periodontal disease increases inseverity parallel the changes described previously in the microbial population collected on artificial crowns during experimentally induced gingivitis. The use of the expressions "microbial flora" or "microbial population" is considered preferable to the terms "plaque", "materia alba", or "debris" in reference to the microbiota of the gingival sulcus region.

Development of dental plaque on epoxy resin crowns in man. A light and electron microscopic study

A method was presented to fabricate epoxy resin crowns to be worn by human subjects requiring full crown restorations. These crowns were utilized in six young adults to study the internal structure of plaque after plaque formation periods of 1 and 3 days, 1 and 3 weeks and 2 months. This study confirmed previous findings that early plaque contains primarily coccal forms, with a shift to predominantly filamentous forms by 3 weeks. Early plaque growth seems to occur by the formation of columnar microcolonies which coalesce and grow by cell division within the colony in a direction perpendicular to the crown surface. Filamentous microorganisms appear in large numbers by 1 week. They appear to colonize the surface of the predominantly coccal plaque, eventually growing into it and replacing the coccal forms. The subgingival, mature plaque contains many motile forms including bacteria with unusual cell wall ultrastructures. Certain bacteria combine into distinctive bacterial aggregations resembling "corn cobs" and "test tube brushes," the latter occurring exclusively in subgingival plaque. Spirochetes appear to grow preferentially on the external surface of subgingival plaque in close contact to the gingival tissue of the deepened sulcus. Their high concentration in the external layer of subgingival plaque suggests that because of their strategic location they may play an important role in the etiology of periodontal disease. Studies of well preserved plaque, possibly combined with the use of serological markers, can serve a useful role in identifying certain microorganisms in dental plaque. Because of their numbers and/or location in relation to periodontal tissues, some of these bacteria may warrant further studies as potential etiologic agents of certain forms of periodontal disease.

Immunoelectron microscopic identification and localization of Streptococcus sanguis with peroxidase-labeled antibody: localization of surface antigens in pure cultures

An indirect method of localizing antigens with horseradish peroxidase-labeled antibody was used to identify and localize surface antigens of Streptococcus sanguis at the ultrastructural level. An electron dense layer surrounding the cell wall could be distinguished without any additional electron microscope staining. This labeled layer represents an immune complex consisting of bacterial surface antigens, specific rabbit antisera, and peroxidase-labeled goat anti-rabbit globulins. Although with undiluted antisera slight cross-reactions occurred with S. salivarius and S. miteor (mitis), these could be readily distinguished from the more intense homologous reaction by their patchiness and the difference in distribution of the label. These cross-reactions were eliminated by appropriate dilutions of the antiserum. No cross-reactions occurred with S. mutans, S. faecalis, Actinomyces species, or Bacterionema, microorganisms wents indicated that horseradish peroxidase can become non-specifically adsorbed to the membrane of certain bacterial cells. Appropriate controls must, therefore, be included for localization of membrane associated antigens with horseradish peroxidase.