Characterization of lectinlike surface components on Capnocytophaga ochracea ATCC 33596 that mediate coaggregation with gram-positive oral bacteria

OxyR inactivation reduces the growth rate and oxidative stress defense in Capnocytophaga ochracea

OBJECTIVE

The human oral cavity harbors several bacteria. Among them, Capnocytophaga ochracea, a facultative anaerobe, is responsible for the early phase of dental plaque formation. In this phase, the tooth surface or tissue is exposed to various oxidative stresses. For colonization in the dental plaque phase, a response by hydrogen peroxide (H₂O₂)-sensing transcriptional regulators, such as OxyR, may be necessary. However, to date, no study has elucidated the role of OxyR protein in C. ochracea.

METHODS

Insertional mutagenesis was used to create an oxyR mutant, and gene expression was evaluated by reverse transcription-polymerase chain reaction and quantitative real-time reverse transcription-polymerase chain reaction. Bacterial growth curves were generated by turbidity measurement, and the sensitivity of the oxyR mutant to H₂O₂ was assessed using the disc diffusion assay. Finally, a two-compartment system was used to assess biofilm formation.

RESULTS

The oxyR mutant grew slower than the wild-type under anaerobic conditions. The agar diffusion assay revealed that the oxyR mutant had increased sensitivity to H₂O₂. The transcript levels of oxidative stress defense genes, sod, ahpC, and trx, were lower in the oxyR mutant than in the wild-type strain. The turbidity of C. ochracea, simultaneously co-cultured with Streptococcus gordonii, was lower than that observed under conditions of homotypic growth. Moreover, the percentage decrease in growth of the oxyR mutant was significantly higher than that of the wild-type.

CONCLUSIONS

These results show that OxyR in C. ochracea regulates adequate in vitro growth and escapes oxidative stress.

β-Glycyrrhetinic acid inhibits the bacterial growth and biofilm formation by supragingival plaque commensals

β-Glycyrrhetinic acid (BGA) is a natural antibacterial agent. Previous studies reported that BGA has antibacterial effects against several bacteria. This study evaluated the effects of BGA on the regulation of supragingival plaque bacteria. First, the minimum inhibitory concentrations (MICs) of BGA against oral bacteria were measured. Next, the minimum concentrations for inhibition of biofilm formation were evaluated against Streptococcus mutans and Streptococcus sobrinus, possessing insoluble glucan synthesis abilities. The MICs of biofilm formation by these bacteria ranged from 1/8 to 2× MIC. Furthermore, the inhibition effects of BGA against the coaggregation of Porphyromonas gingivalis and Streptococcus gordonii were evaluated. BGA at 32 or 64 μg/mL inhibited the coaggregation of these bacteria after a 30 min incubation. Lastly, the inhibition effects of BGA against human supragingival plaque bacteria were evaluated. Human supragingival plaque samples were obtained from 12 healthy donors. The inhibition effects of BGA against biofilm formation by these plaque bacteria were evaluated. Of 12 samples, the biofilm formation by 11 was significantly attenuated by 128-256 μg/mL of BGA. The number of colony forming units in these biofilms was also significantly attenuated. In conclusion, it was revealed that BGA inhibits the growth and biofilm formation of bacteria, furthermore, the same effect was confirmed with supragingival plaque bacteria. BGA is a good candidate for a natural agent that prevents the outbreak and progression of periodontal disease because it suppresses not only the growth and biofilm formation of bacteria, but also the coaggregation of P. gingivalis with plaque bacteria.

Dysbiosis and Variation in Predicted Functions of the Granulation Tissue Microbiome in HPV Positive and Negative Severe Chronic Periodontitis

Retrospective analysis has already shown correlation between severe Chronic Periodontitis (CP) cases with human papiloma virus (HPV). Hence, we aimed to explore deep-seated infected granulation tissue removed during periodontal flap surgery procedures for residential bacterial species between HPV+ and HVP- CP cases, which may serve as good predisposition marker for oral cancer. All CP-granulation samples showed the prominence of Firmicutes, Proteobacteria, and Bacteroidetes phyla with an abundance of gram negative anaerobes, except Streptococcus. In Beta diversity nonmetric multidimensional scaling plot, the random distribution of species was observed between HPV+ and HPV- CP granulation-samples. However, an abundance of Capnocytophaga ochracea was observed in HPV+ CP samples (p<0.05), while Porphyromonas endodontalis, Macellibacteroides fermentas, Treponema phagedenis, and Campylobacter rectus species were highly abundant in HPV- CP samples (p<0.05). The differential species richness leads altered functions related to mismatch-repair and nucleotide excision-repair and cytoskeleton-proteins. Hence, differential abundance of gram negative bacterial species between HPV+ and HPV- granulation-samples under anaerobic conditions may release virulence factors which may alter pathways favouring carcinogenesis. Hence, these species may serve as good predisposition marker for oral-cancer.

Probing of microbial biofilm communities for coadhesion partners

Investigations of interbacterial adhesion in dental plaque development are currently limited by the lack of a convenient assay to screen the multitude of species present in oral biofilms. To overcome this limitation, we developed a solid-phase fluorescence-based screening method to detect and identify coadhesive partner organisms in mixed-species biofilms. The applicability of this method was demonstrated using coaggregating strains of type 2 fimbrial adhesin-bearing actinomyces and receptor polysaccharide (RPS)-bearing streptococci. Specific adhesin/receptor-mediated coadhesion was detected by overlaying bacterial strains immobilized to a nitrocellulose membrane with a suspended, fluorescein-labeled bacterial partner strain. Coadhesion was comparable regardless of which cell type was labeled and which was immobilized. Formaldehyde treatment of bacteria, either in suspension or immobilized on nitrocellulose, abolished actinomyces type 2 fimbrial adhesin but not streptococcal RPS function, thereby providing a simple method for assigning complementary adhesins and glycan receptors to members of a coadhering pair. The method's broader applicability was shown by overlaying colony lifts of dental plaque biofilm cultures with fluorescein-labeled strains of type 2 fimbriated Actinomyces naeslundii or RPS-bearing Streptococcus oralis. Prominent coadhesion partners included not only streptococci and actinomyces, as expected, but also other bacteria not identified in previous coaggregation studies, such as adhesin- or receptor-bearing strains of Neisseria pharyngitis, Rothia dentocariosa, and Kingella oralis. The ability to comprehensively screen complex microbial communities for coadhesion partners of specific microorganisms opens a new approach in studies of dental plaque and other mixed-species biofilms.

Capnocytophaga spp. involvement in bone infections: a review

Capnocytophaga are commensal gliding bacteria that are isolated from human and animal oral flora and are responsible for infections both in immunocompromised and immunocompetent hosts. Accumulation of microbial plaque, loss of collagen attachment, and alveolar bone resorption around the tooth can lead to local Capnocytophaga spp. bone infections. These capnophilic bacteria, from oral sources or following domestic animal bites, are also causative agents of bacteraemia and systemic infections as well as osteomyelitis, septic arthritis, and infections on implants and devices. The present literature review describes the main aetiologies of bone infections due to Capnocytophaga spp., the cellular mechanisms involved, methods used for diagnosis, antimicrobial susceptibility, and effective treatments.

Inhibitory effect of a high-molecular-weight constituent of cranberry on adhesion of oral bacteria

A high-molecular-weight nondialysable material (NDM) isolated from cranberry juice at a concentration of 0.6 to 2.5 mg/ml dissociated coaggregates formed by many intergeneric oral bacteria. A lower concentration of NDM was required to inhibit formation of such coaggregates. NDM acted preferentially on pairs of oral bacteria in which one or both members are Gram-negative anaerobes. The high-molecular-weight material from blueberry also inhibited the coaggregation, although its activity was weaker, whereas such materials obtained from other fruits were inactive. Saliva did not interfere with the ability of NDM to inhibit coaggregation. A preliminary clinical trial showed that NDM reduces S. mutans counts in saliva. The antiadhesion activity of cranberry juice has a potential for altering the oral microbial flora resulting in improved oral hygiene.

Attachment of Fusobacterium nucleatum PK1594 to mammalian cells and its coaggregation with periodontopathogenic bacteria are mediated by the same galactose-binding adhesin

It has been shown that Fusobacterium nucleatum PK1594 coaggregates with Prophyromonas gingivalis PK1924 through a galactose-binding adhesin. In the present study, attachment of F. nucleatum PK1594 to a variety of mammalian cells was characterized. F. nucleatum PK1594 attached to all eukaryotic cells tested, including human buccal epithelial cells, gingival and periodontal ligament fibroblasts, HeLa cells and murine lymphocytes, macrophages, and polymorphonuclear leukocytes. These attachments were (i) inhibited by galactose, lactose and N-acetylgalactosamine and (ii) inhibited by monoclonal antibody specific for the galactose-binding adhesin of F. nucleatum PK1594. In addition, a coaggregation-defective mutant of F. nucleatum PK1594 (PK2172), which does not exhibit galactose binding activity, did not attach to the mammalian cells. Coaggregation of F. nucleatum PK1594 with P. gingivalis PK 1924 and Actinobacillus actinomycetemcomitans JP2, but not with other bacteria, showed a similar pattern with sugars, monoclonal antibody, and the adhesin-deficient mutant. The results suggest that the attachment of F. nucleatum PK1594 to mammalian cells and its coaggregation with periodontal pathogens are mediated by the same galactose-binding adhesin.

Coaggregation between aquatic bacteria is mediated by specific-growth-phase-dependent lectin-saccharide interactions

Coaggregating strains of aquatic bacteria were identified by partial 16S rRNA gene sequencing. The coaggregation abilities of four strains of Blastomonas natatoria and one strain of Micrococcus luteus varied with culture age but were always maximum in the stationary phase of growth. Each member of a coaggregating pair carried either a heat- and protease-sensitive protein (lectin) adhesin or a saccharide receptor, as coaggregation was reversed by sugars.

Coaggregation of Candida dubliniensis with Fusobacterium nucleatum

The binding of microorganisms to each other and oral surfaces contributes to the progression of microbial infections in the oral cavity. Candida dubliniensis, a newly characterized species, has been identified in human immunodeficiency virus-seropositive patients and other immunocompromised individuals. C. dubliniensis phenotypically resembles Candida albicans in many respects yet can be identified and differentiated as a unique Candida species by phenotypic and genetic profiles. The purpose of this study was to determine oral coaggregation (CoAg) partners of C. dubliniensis and to compare these findings with CoAg of C. albicans under the same environmental conditions. Fifteen isolates of C. dubliniensis and 40 isolates of C. albicans were tested for their ability to coaggregate with strains of Fusobacterium nucleatum, Peptostreptococcus micros, Peptostreptococcus magnus, Peptostreptococcus anaerobius, Porphyromonas gingivalis, and Prevotella intermedia. When C. dubliniensis and C. albicans strains were grown at 37 degrees C on Sabouraud dextrose agar, only C. dubliniensis strains coaggregated with F. nucleatum ATCC 49256 and no C. albicans strains showed CoAg. However, when the C. dubliniensis and C. albicans strains were grown at 25 or 45 degrees C, both C. dubliniensis and C. albicans strains demonstrated CoAg with F. nucleatum. Heating the C. albicans strains (grown at 37 degrees C) at 85 degrees C for 30 min or treating them with dithiothreitol allowed the C. albicans strains grown at 37 degrees C to coaggregate with F. nucleatum. CoAg at all growth temperatures was inhibited by mannose and alpha-methyl mannoside but not by EDTA or arginine. The CoAg reaction between F. nucleatum and the Candida species involved a heat-labile component on F. nucleatum and a mannan-containing heat-stable receptor on the Candida species. The CoAg reactions between F. nucleatum and the Candida species may be important in the colonization of the yeast in the oral cavity, and the CoAg of C. dubliniensis by F. nucleatum when grown at 37 degrees C provides a rapid, specific, and inexpensive means to differentiate C. dubliniensis from C. albicans isolates in the clinical laboratory.

Adherence of Peptostreptococcus micros morphotypes to epithelial cells in vitro

Peptostreptococcus micros, which is associated with oral and non-oral mixed anaerobic infections, occurs in three colony morphotypes, the smooth type, the rough type and the smooth variant of the rough type. These types differ in surface structures; the rough type expresses large fibrillar surface appendages, which are absent on the surface of both the smooth and the smooth variant of the rough type. To determine the role of these surface structures in adherence we characterized the adherence of the three morphotypes of P. micros to epithelial cells in vitro. Although all three types adhered well to epithelial cells, adhering numbers of the rough type were significantly lower than those of the smooth and the smooth variant of the rough type. Protease treatment increased the adherence of the rough type of the level of the two other types. The adherence of all three types was reduced more than 85% by treatment with 10 mM sodium periodate. Furthermore, the adherence was pH independent and could not be blocked by incubation with antisera to the bacteria. In addition, we determined the capacity to invade epithelial cells by P. micros. In an acridine orange assay such invasion could not be detected. Our results suggest that the adherence of P. micros to epithelial cells is mediated by periodate-sensitive extracellular polysaccharides and that the protruding fibril-like protein surface structures of the rough type have an obstructive effect on the adherence.

Characterization of a novel N-acetylneuraminic acid-specific Fusobacterium nucleatum PK1594 adhesin

Fusobacterium nucleatum has been identified as significantly associated with sites with active periodontal disease and, as a group, the oral fusobacteria coaggregate with members of all oral bacteria genera tested. Monoclonal antibodies were prepared and used in conjunction with other potential inhibitors, such as simple sugars and amino acids, to characterize coaggregation interactions, of F. nucleatum PK1594. Four unique monoclonal antibodies, 5H11, 14C7, 19F2 and 29C12, were obtained by their ability to inhibit coaggregation of F. nucleatum PK1594 with Actinomyces israelii PK16. They were also capable of inhibiting other coaggregations including Streptococcus oralis H1, S. oralis J22, Capnocytophaga ochracea ATCC33596, Prevotella denticola PK1277 and Prevotella intermedia PK1511. All of these interactions were completely inhibited by N-acetylneuraminic acid. Neither N-acetylneuraminic acid nor monoclonal antibody 5H11 had any inhibitory effect on other F. nucleatum PK1594 interactions, including all galactose-inhibitable coaggregations. The results indicate that F. nucleatum PK1594 expresses upon its surface a distinct type of adhesin that mediates coaggregation interactions that are inhibited by N-acetylneuraminic acid.

Adhesin receptors of human oral bacteria and modeling of putative adhesin-binding domains

Adherence by bacteria to a surface is critical to their survival in the human oral cavity. Many types of molecules are present in the saliva and serous exudates that form the acquired pellicle, a coating on the tooth surface, and serve as receptor molecules for adherent bacteria. The primary colonizing bacteria utilize adhesins to adhere to specific pellicle receptor molecules, then may adhere to other primary colonizers via adhesins, or may present receptor molecules to be utilized by secondary colonizing species. The most common primary colonizing bacteria are streptococci, and six streptococcal cell wall polysaccharide receptor molecules have been structurally characterized. A comparison of the putative adhesin disaccharide-binding regions of the six polysaccharides suggests three groups. A representative of each group was modeled in molecular dynamics simulations. In each case it was found that a loop formed between the galactofuranose beta (Galf beta) and an oxygen of the nearest phosphate group on the reducing side of the Galf beta, that this loop was stabilized by hydrogen bonds, and that within each loop resides the putative disaccharide-binding domain.

Coaggregations among oral bacteria

The oral bacterial community appears to use coaggregation as a major mechanism for interbacterial adhesion and colonization of the host. Methods for measuring and evaluating the specificity of adhesion vary from the visual observation of the phenomenon to quantitative analyses. Not only is aggregation specificity reflected in the choice of partners but also in the fact that many are inhibited by galactosides and sialic acid. Each coaggregation between any two partners within a multigeneric coaggregate is independent of the others and can be shown to be distinct by using the radioactivity-based assay. By using the visual assay, it has been shown that members of the 17 genera of most frequently isolated oral bacteria exhibit coaggregation. With the exception of oral streptococci and a few oral actinomyces, the 17 genera do not exhibit intrageneric coaggregation. As a dynamic population, oral bacteria are in a constant flux of accretion and detachment, which are coupled to growth and death. This ecological community is amenable to intensive study, and the coaggregation assays described here are particularly suited to enhance progress in this study.

Saliva-bacterium interactions in oral microbial ecology

Saliva is thought to have a significant impact on the colonization of microorganisms in the oral cavity. Salivary components may participate in this process by one of four general mechanisms: binding to microorganisms to facilitate their clearance from the oral cavity, serving as receptors in oral pellicles for microbial adhesion to host surfaces, inhibiting microbial growth or mediating microbial killing, and serving as microbial nutritional substrates. This article reviews information pertinent to the molecular interaction of salivary components with bacteria (primarily the oral streptococci and Actinomyces) and explores the implications of these interactions for oral bacterial colonization and dental plaque formation. Knowledge of the molecular mechanisms controlling bacterial colonization of the oral cavity may suggest methods to prevent not only dental plaque formation but also serious medical infections that may follow microbial colonization of the oral cavity.

Characteristics of adherence of Actinobacillus actinomycetemcomitans to epithelial cells

Actinobacillus actinomycetemcomitans smooth variants [SUNY 75(S), SUNY 465, 652] were investigated for their ability to adhere to KB epithelial cells. Both the type of medium (broth versus agar) and anaerobicity influenced adherence levels and cell surface characteristics. Optimal adherence was observed with all three strains after growth of the bacterial cells in broth under anaerobic conditions, a condition which was associated with extracellular microvesicles. Adherence of SUNY 75(S) also was correlated with extracellular amorphous material, whereas adherence of SUNY 465 was also associated with fimbriation which accompanied a smooth to rough phenotype shift. The relationship between adherence and extracellular vesicles, extracellular amorphous material, and fimbriation suggests that all of these components may function in A. actinomycetemcomitans adherence to epithelial cells. The phenotype shift observed in SUNY 465 cells is further evidence that A. actinomycetemcomitans SUNY 465 is predisposed to variant shifts which are associated with changes in adherence and invasion properties.

Localization of the Fusobacterium nucleatum T18 adhesin activity mediating coaggregation with Porphyromonas gingivalis T22

Adherence of pathogenic bacteria is often an essential first step in the infectious process. The ability of bacteria to adhere to one another, or to coaggregate, may be an important factor in their ability to colonize and function as pathogens in the periodontal pocket. Previously, a strong and specific coaggregation was demonstrated between two putative periodontal pathogens, Fusobacterium nucleatum and Porphyromonas gingivalis. The interaction appeared to be mediated by a protein adhesin on the F. nucleatum cells and a carbohydrate receptor on the P. gingivalis cells. In this investigation, we have localized the adhesin activity of F. nucleatum T18 to the outer membrane on the basis of the ability of F. nucleatum T18 vesicles to coaggregate with whole cells of P. gingivalis T22 and the ability of the outer membrane fraction of F. nucleatum T18 to inhibit coaggregation between whole cells of F. nucleatum T18 and P. gingivalis T22. Proteolytic pretreatment of the F. nucleatum T18 outer membrane fraction resulted in a loss of coaggregation inhibition, confirming the proteinaceous nature of the adhesin. The F. nucleatum T18 outer membrane fraction was found to be enriched for several proteins, including a 42-kDa major outer membrane protein which appeared to be exposed on the bacterial cell surface. Fab fragments prepared from antiserum raised to the 42-kDa outer membrane protein were found to partially but specifically block coaggregation. These data support the conclusion that the 42-kDa major outer membrane protein of F. nucleatum T18 plays a role in mediating coaggregation with P. gingivalis T22.

Coaggregation studies of the Eubacterium species

Eubacterium species are gram-positive anaerobic rods that are frequently isolated from subgingival plaque of periodontal pockets. Five Eubacterium species were tested for their ability to coaggregate with 33 oral bacterial strains. Using visual and turbidimetric assays, coaggregation was observed among Eubacterium brachy, Eubacterium nodatum, Eubacterium alactolyticum and Eubacterium limosum strains only when tested with Fusobacterium nucleatum strains; Eubacterium saburreum displayed only weak coaggregation ability. Coaggregation between F. nucleatum and the Eubacterium species was observed over a wide range of concentrations of each organism. The F. nucleatum strains contained a heat labile and the Eubacterium species a heat stabile coaggregation receptor. Arginine, histidine, lysine and glycine inhibited the coaggregation between F. nucleatum and the Eubacterium species. Sugars and other amino acids tested did not inhibit the observed coaggregation. Rabbit anti-F. nucleatum serum completely inhibited coaggregation, but anti-E. brachy serum and normal rabbit serum did not. As these anaerobic microorganisms are frequently isolated from the same oral lesions, the surface interactions observed may be important in the pathogenesis of these polymicrobic infections.

Clustering of an outer membrane adhesin of Haemophilus parainfluenzae

Haemophilus parainfluenzae synthesizes an outer membrane protein adhesin which mediates binding to oral streptococci, salivary pellicle, and neuraminidase-treated erythrocytes. An indirect gold labeling technique and immunoelectron microscopy verified the location of this outer membrane protein. Further, a clustering of gold particles was observed in irregular patches at the cell surface.

Factors in virulence expression and their role in periodontal disease pathogenesis

The classic progression of the development of periodontitis with its associated formation of an inflammatory lesion is characterized by a highly reproducible microbiological progression of a Gram-positive microbiota to a highly pathogenic Gram-negative one. While this Gram-negative microbiota is estimated to consist of at least 300 different microbial species, it appears to consist of a very limited number of microbial species that are involved in the destruction of periodontal diseases. Among these "putative periodontopathic species" are members of the genera Porphyromonas, Bacteroides, Fusobacterium, Wolinella, Actinobacillus, Capnocytophaga, and Eikenella. While members of the genera Actinomyces and Streptococcus may not be directly involved in the microbial progression, these species do appear to be essential to the construction of the network of microbial species that comprise both the subgingival plaque matrix. The temporal fluctuation (emergence/disappearance) of members of this microbiota from the developing lesion appears to depend upon the physical interaction of the periodontal pocket inhabitants, as well as the utilization of the metabolic end-products of the respective species intimately involved in the disease progression. A concerted action of the end-products of prokaryotic metabolism and the destruction of host tissues through the action of a large number of excreted proteolytic enzymes from several of these periodontopathogens contribute directly to the periodontal disease process.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrageneric coaggregation among strains of human oral bacteria: potential role in primary colonization of the tooth surface

Of the 122 human oral bacterial strains tested from 11 genera, only streptococci and a few actinomyces exhibited coaggregation among the strains within their respective genera. Eight of the ten streptococci showed multiple intrageneric coaggregations, all of which were inhibited by galactosides. The widespread intrageneric coaggregation among the streptococci and the less extensive coaggregation among the actinomyces offers an explanation for their accretion on cleaned tooth surfaces and their dominance as primary colonizers.

Identification of the rhamnose-sensitive adhesin of Capnocytophaga ochracea ATCC 33596

The coaggregation of the Gram-negative microorganism Capnocytophaga ochracea ATCC 33596 with several Gram-positive bacteria, including streptococci, actinomyces and rothia, is mediated by rhamnose-sensitive adhesin(s). In the present study, MAbs against the C. ochracea adhesin(s) were prepared. These antibodies inhibited all the rhamnose-sensitive interactions, indicating that they recognize epitopes at or near the rhamnose binding site of the adhesin. The monoclonals served as probes in immunoblot analysis and recognized a polypeptide of Mr 155 K present in the wild-type organism but absent in a coaggregation defective mutant. It is concluded that the rhamnose-sensitive interactions of C. ochracea are mediated by a 155 K Mr polypeptide present on its outer surface.

Characterization of coaggregation between Bacteroides gingivalis T22 and Fusobacterium nucleatum T18

Bacterial adherence is a key factor in the colonization of the oral ecosystem, yet little is known about the mechanisms by which the pathogen Bacteroides gingivalis adheres in the periodontal environment. We examined the ability of strains of B. gingivalis to coaggregate with selected microorganisms isolated from the subgingival microbiota of the cynomolgus monkey. A strong interaction was demonstrated between strains of B. gingivalis and Fusobacterium nucleatum, whereas less pronounced or no interaction was observed with other oral isolates. Electron microscopic examination of coaggregates revealed large masses of bacteria, in which the fusiform F. nucleatum T18 and coccobacillary B. gingivalis T22 cells formed a woven pattern. To investigate this interaction and the nature of the bacterial cell surface molecules involved, we used a microcoaggregation assay. Galactose and galactose-related sugars blocked coaggregation, in contrast with the lack of effect of glucose or glucose-related sugars. The ability of F. nucleatum T18 cells to coaggregate was diminished by pretreatment with pronase. Pretreatment of B. gingivalis T22 cells with pronase resulted in an inhibition of coaggregation, whereas pretreatment with sodium metaperiodate completely abolished coaggregation. These data suggest that the coaggregation between B. gingivalis T22 and F. nucleatum T18 represents a carbohydrate-lectin interaction, mediated by a galactose-containing carbohydrate on B. gingivalis T22 and a protein on F. nucleatum T18.

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.

Isolation of a coaggregation-inhibiting cell wall polysaccharide from Streptococcus sanguis H1

Coaggregation between Streptococcus sanguis H1 and Capnocytophaga ochracea ATCC 33596 cells is mediated by a carbohydrate receptor on the former and an adhesin on the latter. Two methods were used to release the carbohydrate receptor from the gram-positive streptococcus, autoclaving and mutanolysin treatment. The polysaccharide released from the streptococcal cell wall by either treatment was purified by ion-exchange chromatography; this polysaccharide inhibited coaggregation when preincubated with the gram-negative capnocytophaga partner. After hydrolysis of the polysaccharide by hydrofluoric acid (HF), the major oligosaccharide of the polysaccharide was purified by high-performance liquid chromatography. By analysis of the HF hydrolysis of the polysaccharide and the purified oligosaccharide, this major oligosaccharide appeared to be the repeating unit of the polysaccharide, with minor components resulting from internal hydrolysis of the major oligosaccharide. Gas chromatography results showed that the oligomer was a hexasaccharide, consisting of rhamnose, galactose, and glucose, in the ratio of 2:3:1, respectively. By weight, the purified hexasaccharide was a fourfold-more-potent inhibitor of coaggregation than the native polysaccharide. Resistance to hydrolysis by sulfuric acid alone and susceptibility to hydrolysis by HF suggested that oligosaccharide chains of the polysaccharide are linked by phosphodiester bonds. Studies with a coaggregation-defective mutant of S. sanguis H1 revealed that the cell walls of the mutant contained neither the polysaccharide nor the hexasaccharide repeating unit. The purification of both a polysaccharide and its constituent hexasaccharide repeating unit, which both inhibited coaggregation, and the absence of this polysaccharide or hexasaccharide on a coaggregation-defective mutant strongly suggest that the hexasaccharide derived from the polysaccharide functions as the receptor for the adhesin from C. ochracea ATCC 33596.

Coaggregation properties of human oral Veillonella spp.: relationship to colonization site and oral ecology

The primary habitats of oral veillonellae are the tongue, dental plaque, and the buccal mucosa. Isolates were obtained from each habitat and tested for coaggregation with a battery of other oral bacterial strains. All 59 tongue isolates tested for coaggregation were Veillonella atypica or Veillonella dispar. All but one of them coaggregated with strains of Streptococcus salivarius, a predominant inhabitant of the tongue surface but not subgingival dental plaque. These tongue isolates were unable to coaggregate with most normal members of the subgingival flora such as Actinomyces viscosus, Actinomyces naeslundii, Actinomyces israelii, and Streptococcus sanguis. In contrast, 24 of 29 Veillonella isolates, of which 20 were Veillonella parvula from subgingival dental plaque samples, coaggregated strongly with the three species of Actinomyces, S. sanguis, and other bacteria usually present in subgingival plaque, but they did not coaggregate with S. salivarius. The majority of isolates from the buccal mucosa (42 of 55) has coaggregation properties like those from the tongue. These results indicate that the three human oral Veillonella species are distributed on oral surfaces that are also occupied by their coaggregation partners and thus provide strong evidence that coaggregation plays a critical role in the bacterial ecology of the oral cavity.

Intergeneric rosettes: sequestered surface recognition among human periodontal bacteria

The human oral bacteria, Streptococcus sanguis and Bacteroides loescheii, when mixed in equal numbers in vitro, formed large settling coaggregates. As the relative number of each cell type was changed, coaggregates became smaller until at cell-type ratios of 10 to 1, rosettes formed. Rosettes consisting of a streptococcal cell in the center surrounded by bacteroides cells exhibited surface recognition properties of only the bacteroides, which coaggregated with many other cell types such as Actinomyces naeslundii, and formed large settling multigeneric aggregates. The ecological significance of these results derives from the following: (i) the direct demonstration that intergeneric coaggregates can protect the central cell from or prevent its access to other cells in the environment, and (ii) the potential for these effects to occur during bacterial succession of various cell types observed in progressively more severe stages of human periodontal disease.