Interaction of Fusobacterium nucleatum 191 with human peripheral blood lymphocytes

Low Abundance Fusobacterium Nucleatum Supports Early Pregnancy Development - An In Vitro Study

Pregnancy success depends greatly on a balanced immune homeostasis. The detection of bacterial components in the upper reproductive tract in non-pregnant and pregnant women raised questions on its possible beneficial role in reproductive health. The local conditions that allow the presence of bacteria to harmonize with the establishment of pregnancy are still unknown. Among the described bacterial species in endometrial and placental samples, Fusobacterium nucleatum was found. It has been observed that F. nucleatum can induce tumorigenesis in colon carcinoma, a process that shares several features with embryo implantation. We propose that low concentrations of F. nucleatum may improve trophoblast function without exerting destructive responses. Inactivated F. nucleatum and E. coli were incubated with the trophoblastic cell lines HTR8/SVneo, BeWo, and JEG-3. Viability, proliferation, migratory capacity, invasiveness and the secretion of chemokines, other cytokines and matrix metalloproteinases were assessed. The presence of F. nucleatum significantly induced HTR8/SVneo invasion, accompanied by the secretion of soluble mediators (CXCL1, IL-6 and IL-8) and metalloproteinases (MMP-2 and MMP-9). However, as concentrations of F. nucleatum increased, these did not improve invasiveness, hindered migration, reduced cell viability and induced alterations in the cell cycle. Part of the F. nucleatum effects on cytokine release were reverted with the addition of a TLR4 blocking antibody. Other effects correlated with the level of expression of E-cadherin on the different cell lines tested. Low amounts of F. nucleatum promote invasion of HTR8/SVneo cells and induce the secretion of important mediators for pregnancy establishment. Some effects were independent of LPS and correlated with the expression of E-cadherin on trophoblasts.

Laboratory maintenance of fusobacteria

This unit describes routine laboratory handling of fusobacteria. Different media that can be used to grow or enrich Fusobacterium nucleatum and other species of this genus are described. The growth and stock conditions as well as the susceptibility of F. nucleatum to oxygen in a pure culture are also discussed.

Association of a high-molecular weight arginine-binding protein of Fusobacterium nucleatum ATCC 10953 with adhesion to secretory immunoglobulin A and coaggregation with Streptococcus cristatus

INTRODUCTION

Fusobacterium nucleatum coaggregates with a diverse range of bacterial species, and binds to host tissues and proteins such as immunoglobulin. These interactions may support the attachment of a variety of organisms to oral surfaces and can facilitate the invasion of soft tissues. We hypothesized that coaggregation with streptococci and immunoglobulin binding may occur by a common adhesin sensitive to l-arginine.

METHODS

Repeated mixing of F. nucleatum with non-immune secretory immunoglobulin A (S-IgA) and recovery of non-agglutinating cells isolated a spontaneous mutant (isolate 21) of F. nucleatum that was defective in S-IgA binding. Wild-type and mutant F. nucleatum were compared by coaggregation and adhesion assays.

RESULTS

Isolate 21 exhibited significantly reduced S-IgA binding and coaggregation with oral streptococci but not with Porphyromonas gingivalis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the mutant was deficient compared to wild-type for a single protein of approximately 360 kilodaltons. The corresponding protein was isolated from wild-type F. nucleatum protein preparations by coprecipitation with arginine-agarose beads. This protein was able to bind both Streptococcus cristatus and S-IgA. Mass spectrometry analysis indicated that this protein was closely related to putative autotransporter proteins in other F. nucleatum strains and was a 100% match to the deduced amino acid sequence of a 10,638-base-pair open reading frame in the incomplete genome sequence of F. nucleatum ATCC 10,953. Peptides identified by MS-MS analysis spanned most of the predicted amino acid sequence, suggesting that the mature protein is not subject to postsecretory cleavage.

CONCLUSION

Coaggregation represents a novel function within the autotransporter class of proteins, which are often associated with virulence.

Fusobacterium nucleatum transports noninvasive Streptococcus cristatus into human epithelial cells

Analysis of human buccal epithelial cells frequently reveals an intracellular polymicrobial consortium of bacteria. Although several oral bacteria have been demonstrated to invade cultured epithelial cells, several others appear unable to internalize. We hypothesized that normally noninvasive bacteria may gain entry into epithelial cells via adhesion to invasive bacteria. Fusobacterium nucleatum is capable of binding to and invading oral epithelial cells. By contrast, Streptococcus cristatus binds weakly to host cells and is not internalized. F. nucleatum and S. cristatus coaggregate strongly via an arginine-sensitive interaction. Coincubation of KB or TERT-2 epithelial cells with equal numbers of F. nucleatum and S. cristatus bacteria led to significantly increased numbers of adherent and internalized streptococci. F. nucleatum also promoted invasion of KB cells by other oral streptococci and Actinomyces naeslundii. Dissection of fusobacterial or streptococcal adhesive interactions by using sugars, amino acids, or antibodies demonstrated that this phenomenon is due to direct attachment of S. cristatus to adherent and invading F. nucleatum. Inhibition of F. nucleatum host cell attachment and invasion with galactose, or fusobacterial-streptococcal coaggregation by the arginine homologue l-canavanine, abrogated the increased S. cristatus adhesion to, and invasion of, host cells. In addition, polyclonal antibodies to F. nucleatum, which inhibited fusobacterial attachment to both KB cells and S. cristatus, significantly decreased invasion by both species. Similar decreases were obtained when epithelial cells were pretreated with cytochalasin D, staurosporine, or cycloheximide. These studies indicate that F. nucleatum may facilitate the colonization of epithelial cells by bacteria unable to adhere or invade directly.

Identification and characterization of a novel adhesin unique to oral fusobacteria

Fusobacterium nucleatum is a gram-negative anaerobe that is prevalent in periodontal disease and infections of different parts of the body. The organism has remarkable adherence properties, binding to partners ranging from eukaryotic and prokaryotic cells to extracellular macromolecules. Understanding its adherence is important for understanding the pathogenesis of F. nucleatum. In this study, a novel adhesin, FadA (Fusobacterium adhesin A), was demonstrated to bind to the surface proteins of the oral mucosal KB cells. FadA is composed of 129 amino acid (aa) residues, including an 18-aa signal peptide, with calculated molecular masses of 13.6 kDa for the intact form and 12.6 kDa for the secreted form. It is highly conserved among F. nucleatum, Fusobacterium periodonticum, and Fusobacterium simiae, the three most closely related oral species, but is absent in the nonoral species, including Fusobacterium gonidiaformans, Fusobacterium mortiferum, Fusobacterium naviforme, Fusobacterium russii, and Fusobacterium ulcerans. In addition to FadA, F. nucleatum ATCC 25586 and ATCC 49256 also encode two paralogues, FN1529 and FNV2159, each sharing 31% identity with FadA. A double-crossover fadA deletion mutant, F. nucleatum 12230-US1, was constructed by utilizing a novel sonoporation procedure. The mutant had a slightly slower growth rate, yet its binding to KB and Chinese hamster ovarian cells was reduced by 70 to 80% compared to that of the wild type, indicating that FadA plays an important role in fusobacterial colonization in the host. Furthermore, due to its uniqueness to oral Fusobacterium species, fadA may be used as a marker to detect orally related fusobacteria. F. nucleatum isolated from other parts of the body may originate from the oral cavity.

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.

Fusobacterium nucleatum T18 aggregates human mononuclear cells and inhibits their PHA-stimulated proliferation

In previous studies Fusobacterium nucleatum has been shown to induce either stimulatory or inhibitory effects on human mononuclear cells. We examined the interaction of human mononuclear cells with human and cynomolgus monkey strains of F. nucleatum. Peripheral blood mononuclear cells (PBMCs) isolated from normal donors were aggregated in the presence of cells of F. nucleatum but not control bacteria. The aggregation of PBMCs and F. nucleatum T18 was inhibited by either L-arginine, L-lysine, or pretreatment of the bacterial cells with heat, but was unaffected by the presence of sugars or normal human serum. Strain T18 aggregated purified T-cells and monocytes at approximately equal concentrations. When F. nucleatum T18 was incubated with PHA-stimulated PBMCs, DNA synthesis in the PBMCs was significantly inhibited and detection of IL-2R alpha on the PBMCs was reduced. These studies indicate that F. nucleatum aggregates PBMCs, and that this interaction is associated with both an inhibition of PBMC proliferation and a decrease in IL-2 receptor expression. The ability of F. nucleatum to inhibit mononuclear cell proliferation may be significant in the pathogenesis of periodontal diseases.

Mechanisms of adhesion by oral bacteria

Adherence to a surface is a key element for colonization of the human oral cavity by the more than 500 bacterial taxa recorded from oral samples. Three surfaces are available: teeth, epithelial mucosa, and the nascent surface created as each new bacterial cell binds to existing dental plaque. Oral bacteria exhibit specificity for their respective colonization sites. Such specificity is directed by adhesin-receptor cognate pairs on genetically distinct cells. Colonization is successful when adherent cells grow and metabolically participate in the oral bacterial community. The potential roles of adherence-relevant molecules are discussed in the context of the dynamic nature of the oral econiche.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Intergeneric coaggregation of oral Treponema spp. with Fusobacterium spp. and intrageneric coaggregation among Fusobacterium spp

A total of 22 strains of Treponema spp. including members of all four named human oral species were tested for coaggregation with 7 strains of oral fusobacteria, 2 strains of nonoral fusobacteria, and 45 strains of other oral bacteria, which included actinobacilli, actinomyces, capnocytophagae, eubacteria, porphyromonads, prevotellae, selenomonads, streptococci, and veillonellae. None of the treponemes coaggregated with any of the latter 45 oral strains or with the two nonoral fusobacteria. All treponemes, eight Treponema denticola strains, eight T. socranskii strains, four oral pectinolytic treponemes, one T. pectinovorum strain, and one T. vincentii strain coaggregated with at least one strain of the fusobacteria tested as partners. The partners consisted of one strain of Fusobacterium periodonticum, five F. nucleatum strains including all four subspecies of F. nucleatum, and a strain of F. simiae obtained from the dental plaque of a monkey. In the more than 100 coaggregations observed, the fusobacterial partner was heat inactivated (85 degrees C for 30 min), while the treponemes were unaffected by the heat treatment. Furthermore, the fusobacteria were usually inactivated by proteinase K treatment, and the treponemes were not affected. Only the T. denticola coaggregations were inhibited by lactose and D-galactosamine. None were inhibited by any of 23 other different sugars or L-arginine. Intragenic coaggregations were seen among the subspecies of F. nucleatum and with F. periodonticum, and none were inhibited by any of the sugars tested or by L-arginine. No intrageneric coaggregations were observed among the treponemes. These data indicate that the human oral treponemes show a specificity for oral fusobacteria as coaggregation partners. Such cell-to cell contact may facilitate efficient metabolic communication and enhance the proliferation of each cell in the progressively more severe stages of periodontal disease.

Effect of sonicated material from Fusobacterium nucleatum on the functional capacity of accessory cells derived from dental pulp

Fusobacterium nucleatum-derived components were studied for their effect on the ability of accessory pulpal cells to induce T-lymphocyte proliferation. In initial experiments, spleen cells were used to establish concentration ranges at which testing of the effect of the bacterial components would be suitable. At low concentrations, bacterial substances induced a stimulatory effect on the proliferation rate of spleen cells, but not when purified T-lymphocytes were incubated in the presence of concanavalin A and pulpal accessory cells. At increasing concentrations, a dose-dependent reduction was observed. Pretreatment with the bacterial products for 4 h gave a stimulatory effect in the absence of concanavalin A for both spleen cells and T-lymphocytes. Removal of low-molecular weight components (<3.5 kDa) did not influence the inhibitory effect, whereas preheating the bacterial substances to 100 degrees C eliminated the observed inhibition. Findings show that heat-sensitive, high-molecular-weight components of F. nucleatum can evoke a concentration-dependent stimulatory or suppressive effect on the proliferation rate of T-lymphocytes in the presence of accessory cells derived from the dental pulp.

A non-lectin-like mechanism by which Fusobacterium nucleatum 10953 adheres to and activates human lymphocytes

Most (approximately 80%) strains of Fusobacterium nucleatum adhere to human erythrocytes in a lectin-like manner that is strongly inhibited by N-acetyl-D-galactosamine (GalNAc). In this study, we investigated the capacity of F. nucleatum 10953, a strain that is weakly inhibited by GalNAc, to adhere to and activate human lymphocytes in vitro. Experiments using [3H]-labeled bacteria and scanning electron microscopy clearly showed that 10953 adhered to lymphocytes and that adherence was blocked by L-arginine+GalNAc greater than L-arginine much greater than GalNAc. Adherence was Ca(2+)-dependent, inhibited by pretreatment of the bacteria with proteases or heat, and unaffected by paraformaldehyde fixation of the bacteria. Strain 10953 induced lymphocyte mitogenesis that was blocked by L-arginine but not by GalNAc. These results suggest that certain strains of F. nucleatum, such as 10953, express a distinct, non-lectin-like mechanism by which they adhere to and activate lymphocytes. Activation of lymphocytes may be an important mechanism in the pathogenesis of periodontal diseases associated with these bacteria.