Fimbriation of Actinobacillus actinomycetemcomitans

The product of tadZ, a new member of the parA/minD superfamily, localizes to a pole in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans establishes a tenacious biofilm that is important for periodontal disease. The tad locus encodes the components for the secretion and biogenesis of Flp pili, which are necessary for the biofilm to form. TadZ is required, but its function has been elusive. We show that tadZ genes belong to the parA/minD superfamily of genes and that TadZ from A. actinomycetemcomitans (AaTadZ) forms a polar focus in the cell independent of any other tad locus protein. Mutations indicate that regions in AaTadZ are required for polar localization and biofilm formation. We show that AaTadZ dimerizes and that all TadZ proteins are predicted to have a Walker-like A box. However, they all lack the conserved lysine at position 6 (K6) present in the canonical Walker-like A box. When the alanine residue (A6) in the atypical Walker-like A box of AaTadZ was converted to lysine, the mutant protein remained able to dimerize and localize, but it was unable to allow the formation of a biofilm. Another essential biofilm protein, the ATPase (AaTadA), also localizes to a pole. However, its correct localization depends on the presence of AaTadZ. We suggest that the TadZ proteins mediate polar localization of the Tad secretion apparatus.

The tad locus: postcards from the widespread colonization island

The Tad (tight adherence) macromolecular transport system, which is present in many bacterial and archaeal species, represents an ancient and major new subtype of type II secretion. The tad genes are present on a genomic island named the widespread colonization island (WCI), and encode the machinery that is required for the assembly of adhesive Flp (fimbrial low-molecular-weight protein) pili. The tad genes are essential for biofilm formation, colonization and pathogenesis in the genera Aggregatibacter (Actinobacillus), Haemophilus, Pasteurella, Pseudomonas, Yersinia, Caulobacter and perhaps others. Here we review the structure, function and evolution of the Tad secretion system.

Influence of genetic background on transformation and expression of Green Fluorescent Protein in Actinobacillus actinomycetemcomitans

BACKGROUND/AIMS

The development of an electro-transformation system and the construction of shuttle plasmids for Actinobacillus actinomycetemcomitans have enhanced the molecular analysis of virulence factors. However, inefficient transformation is frequently encountered. This study investigated the efficiency of electro-transformation and expression of Green Fluorescent Protein (GFP) in 12 different A. actinomycetemcomitans strains. The influence of the plasmid vector, serotype, and phenotype were the major factors taken into consideration.

MATERIAL AND METHODS

Twelve serotyped A. actinomycetemcomitans strains were independently electro-transformed with two different Escherichia coli-A. actinomycetemcomitans shuttle plasmids (pVT1303 and pVT1304), both containing an identical ltx-GFPmut2 gene construct but a different backbone (pDMG4 and pPK1, respectively). The transformation efficiency, transformation frequency, and electro-transformation survival rate were determined by culture techniques. GFP expression was observed at the colony level by fluorescence microscopy.

RESULTS

All strains could be transformed with both plasmids. However, major differences were observed for the transformation efficiency, transformation frequency, and electro-transformation survival rate between strains. The data demonstrated that plasmid vector, serotype, and phenotype are key players for obtaining a successful transformation. An inverted relationship between the electro-transformation survival rate and tranformation frequency was also observed. GFP expression was also influenced by phenotype, serotype and plasmid vector.

CONCLUSIONS

The serotype of A. actinomycetemcomitans has an important influence on its survival after electro-transformation and on transformation frequency. The expression of GFP is strain and plasmid vector dependent.

Mutation analysis of the flp operon in Actinobacillus actinomycetemcomitans

Fresh clinical isolates of the periodontal pathogen Actinobacillus actinomycetemcomitans live as autoaggregates, in which cells are densely packed and embedded in an extracellular matrix composed of bundled fimbriae, exopolymers, and vesicles. The expression of fimbriae is known to be determined by the flp operon of 14 genes, flp-1-flp-2-tadV-rcpCAB-tadZABCDEFG. We generated mutations of each gene of this operon in A. actinomycetemcomitans strain D7S. All mutants expressed some changes in the production of extracellular matrix materials that include vesicles, exopolymers, and fimbriae. The expression of fimbriae required the function of flp-1, rcpA, rcpB, tadB, tadD, tadE, and tadF. Mutants of flp-2, tadZ, tadA, tadC, and tadG expressed reduced levels of fimbriae, or fimbriae that had different gross appearance. Importantly, the expression of the non-fimbrial matrix materials was affected by all mutations, suggesting that the flp operon was involved in production of these materials. The flp locus apparently plays a central role in autoaggregation of A. actinomycetemcomitans, which may be the primary survival strategy of this bacterium in vivo.

Peptide methionine sulfoxide reductase (MsrA) is not a major virulence determinant for the oral pathogen Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is an oral pathogen that is a causative agent for periodontal disease as well as other non-oral infections. The chronic inflammation associated with periodontal diseases suggests that the bacterium must be able to neutralize oxygen intermediates to survive in the host tissues. Methionine sulfoxide reductase (MsrA) is an enzyme that has been demonstrated to have a role in protection against oxidative damage and has also been identified to be required for the proper expression or maintenance of functional adhesins on the surface of several pathogenic bacteria. The A. actinomycetemcomitans homologue of msrA has been isolated and a chromosomal insertion mutant constructed by allele replacement mutagenesis. Inactivation of the gene led to a complete loss of enzymic activity toward a synthetic substrate. However, the isogenic mutant was not more sensitive to oxidative stress or less adherent to epithelial cells as compared with the parent strain. These data suggest that this strain of A. actinomycetemcomitans has redundant systems that compensate for the MsrA activities ascribed for other organisms.

Cell surface-associated enolase in Actinobacillus actinomycetemcomitans

Cell surface-associated materials of Actinobacillus actinomycetemcomitans were extracted by a short incubation of the cell suspension in a Tris-buffered saline in the presence and absence of a restriction enzyme, EcoRI. The supernatants (which we termed EcoRI extract and surface extract, respectively) contained a number of extracellularly released proteins. Of these proteins, four major proteins were identified by N-terminal sequencing to be the 34 and 39 kDa outer membrane proteins, the GroEL-like protein, and a 47 kDa protein homologous to Haemophilus influenzae enolase. Enolase activity was found in the extracts and its relative amount of activity in the EcoRI extract from a culture of the mid-exponential growth phase was estimated as 5.7% of total enzyme activity. In contrast, the relative amount of activity of another cytosolic enzyme, lactate dehydrogenase, was extremely low in the extracts and also in the culture supernatant. These results suggest the external localization of enolase in this bacterium.

impA, a gene coding for an inner membrane protein, influences colonial morphology of Actinobacillus actinomycetemcomitans

Directed mutagenesis of a gene coding for a membrane protein of the periodontopathogen Actinobacillus actinomycetemcomitans was achieved by conjugation. The gene was disrupted by insertion of an antibiotic cassette into a unique endonuclease restriction sequence engineered by inverse PCR. The disrupted gene was cloned into a conjugative plasmid and transferred from Escherichia coli to A. actinomycetemcomitans. The allelic replacement mutation resulted in the loss of a 22-kDa inner membrane protein. The loss of this protein (ImpA) resulted in changes in the outer membrane protein composition of the bacterium. Concurrent with the mutation in impA was a change in the pattern of growth of the mutant bacteria in broth cultures. The progenitor bacteria grew as a homogeneous suspension of cells compared to a granular, autoaggregating adherent cell population described for the mutant bacteria. These data suggest that ImpA may play a regulatory role or be directly involved in protein(s) that are exported and associated with colony variations in A. actinomycetemcomitans.

Bacterial adhesion of Actinobacillus actinomycetemcomitans serotypes to titanium implants: SEM evaluation. A preliminary report

BACKGROUND

In this study, the adherence ability of Actinobacillus actinomycetemcomitans serotypes to titanium implant surfaces was evaluated to demonstrate if any selective adherence occurs according to the serotypes of the microorganism.

METHODS

The study material included 3 reference strains of A. actinomycetemcomitans serotypes a, b, and c (ATCC 29523, ATCC 43718, ATCC 33384) and 2 clinical isolates of A. actinomycetemcomitans serotypes d and e (IDH 781, IDH 1705), together with commercially available titanium blade implants. For each strain, bacterial suspensions with identical concentrations (5 x 10(7) cells/ml) were prepared and 0.5 ml of each was added on to the implant surfaces, which had been precoated with glycine-bovine serum albumin (BSA). After incubation at 37 degrees C for 60 minutes in 5% CO2 in air, the implants with attached bacteria were prepared for scanning electron microscopic (SEM) observations. Bacterial adhesion was quantified on the textured body surfaces of the implants, and results were statistically analyzed with analysis of variance followed by Duncan's test. The surface ultrastructure of the bacterial cells was also evaluated descriptively.

RESULTS

The tested strains adhered to implant surfaces in different quantities. Serotype a (ATCC 29523) showed the highest adherence affinity (statistically significant, P <0.01). When compared with each other, serotypes b, c, and d (ATCC 43718, ATCC 33384, and IDH 781) attached equally well, whereas serotype e (IDH 1705) had a statistically significant low adherence capability.

CONCLUSIONS

It is suggested that in vitro A. actinomycetemcomitans adhesion to implant surfaces is strain dependent.

Identification and molecular analysis of rough-colony-specific outer membrane proteins of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans, a gram-negative bacterium isolated from the human mouth, has been implicated in the pathogenesis of early-onset periodontitis. Primary isolates cultured from subgingival plaque exhibit an adherent, rough colony phenotype which spontaneously converts to a nonadherent, smooth phenotype upon in vitro subculture. The rough colony variant produces abundant fimbriae and autoaggregates, while the smooth colony variant is planktonic and produces scant fimbriae. To begin to understand the significance of colony variation in biofilm formation by A. actinomycetemcomitans, outer membrane protein profiles of four isogenic rough and smooth colony variants were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two proteins with relative molecular masses of 43 and 20 kDa were expressed by the rough colony variants exclusively. Expression of these proteins was not found to be dependent on growth phase, oxygen tension, or type of complex medium. N-terminal amino acid sequences of these proteins obtained by Edman degradation were compared with sequences from the University of Oklahoma A. actinomycetemcomitans genome database. Two contiguous open reading frames (ORFs) encoding proteins having sequence homology with these proteins were identified. The 43-kDa protein (RcpA [rough colony protein A]) was similar to precursor protein D of the general secretion pathway of gram-negative bacilli, while the 20-kDa protein (RcpB [rough colony protein B]) appeared to be unique. The genes encoding these proteins have been cloned from A. actinomycetemcomitans 283 and sequenced. A BLASTX (gapped BLAST) search of the surrounding ORFs revealed homology with other fimbria-related proteins. These data suggest that the genes encoding the 43-kDa (rcpA) and 20-kDa (rcpB) proteins may be functionally related to each other and to genes that may encode fimbria-associated proteins.

Virulence factors of Actinobacillus actinomycetemcomitans

A. actinomycetemcomitans has clearly adapted well to its environs; its armamentarium of virulence factors (Table 2) ensures its survival in the oral cavity and enables it to promote disease. Factors that promote A. actinomycetemcomitans colonization and persistence in the oral cavity include adhesins, bacteriocins, invasins and antibiotic resistance. It can interact with and adhere to all components of the oral cavity (the tooth surface, other oral bacteria, epithelial cells or the extracellular matrix). The adherence is mediated by a number of distinct adhesins that are elements of the cell surface (outer membrane proteins, vesicles, fimbriae or amorphous material). A. actinomycetemcomitans enhances its chance of colonization by producing actinobacillin, an antibiotic that is active against both streptococci and Actinomyces, primary colonizers of the tooth surface. The fact that A. actinomycetemcomitans resistance to tetracyclines, a drug often used in the treatment of periodontal disease, is on the rise is an added weapon. Periodontal pathogens or their pathogenic products must be able to pass through the epithelial cell barrier in order to reach and cause destruction to underlying tissues (the gingiva, cementum, periodontal ligament and alveolar bone). A. actinomycetemcomitans is able to elicit its own uptake into epithelial cells and its spread to adjacent cells by usurping normal epithelial cell function. A. actinomycetemcomitans may utilize these remarkable mechanisms for host cell infection and migration to deeper tissues. A. actinomycetemcomitans also orchestrates its own survival by elaborating factors that interfere with the host's defense system (such as factors that kill phagocytes and impair lymphocyte activity, inhibit phagocytosis and phagocyte chemotaxis or interfere with antibody production). Once the organisms are firmly established in the gingiva, the host responds to the bacterial onslaught, especially to the bacterial lipopolysaccharide, by a marked and continual inflammatory response, which results in the destruction of the periodontal tissues. A. actinomycetemcomitans has at least three individual factors that cause bone resorption (lipopolysaccharide, proteolysis-sensitive factor and GroEL), as well as a number of activities (collagenase, fibroblast cytotoxin, etc.) that elicit detrimental effects on connective tissue and the extracellular matrix. It is of considerable interest to know that A. actinomycetemcomitans possesses so many virulence factors but unfortunate that only a few have been extensively studied. If we hope to understand and eradicate this pathogen, it is critical that in-depth investigations into the biochemistry, genetic expression, regulation and mechanisms of action of these factors be initiated.

Epithelial cell invasion by Actinobacillus actinomycetemcomitans strains from restriction fragment-length polymorphism groups associated with juvenile periodontitis or carrier status

The epithelial cell invasiveness of Actinobacillus actinomycetemcomitans strains of different restriction fragment-length polymorphism (RFLP) groups associated with disease conversion and asymptomatic carrier status in localized juvenile periodontitis was examined. Twenty clinical isolates were studied for their ability to invade KB monolayers, using the quantitative gentamicin killing assay. Five isolates were found to be invasive, five were not invasive; and the other 10 did not invade better than an invasion negative control Haemophilus aphrophilus strain ATCC 19415. Using probe-specific DNA fingerprinting. 11 strains were assigned to RFLP group II (disease-associated); 4 to RFLP type XIII (carrier status associated); and the other to groups III, IV, V and VII. Eight isolates, all RFLP group II, were leukotoxin producers as determined by PCR amplification of the lkt promoter region. No correlation was found between invasiveness and RFLP group. Leukotoxin production was more associated with noninvasive than invasive strains.

The importance of fimbriae in the virulence and ecology of some oral bacteria

Cumulative evidence indicates that bacterial adherence to mucosal and tooth surfaces as well as bacterial coaggregation are essential steps for colonization of various oral bacterial species. Bacterial fimbriae have been shown to play an important role in the interaction between bacteria and host cells or among bacterial cells. The properties of fimbriae from selected species of oral bacteria are discussed in terms of virulence traits and ecological significance. Among others, Porphyromonas gingivalis fimbriae have been most extensively studied. The fimbrial structure is composed of 41-kDa fimbrillin proteins. DNA sequencing of the fimbrillin gene (fimA) from nine strains of P. gingivalis suggests intraspecies variation in the structure of fimA, while retaining common immunochemical specificities. P. gingivalis fimbriae exhibit a wide variety of biological activities including immunogenicity, binding to various host proteins, stimulation of cytokine production and promotion of bone resorption, Actinobacillus actinomycetemcomitans also possesses fimbriae; however, little is known concerning their chemical, genetical, and biological properties. Fimbriae of Prevotella intermedia are shown to induce hemagglutination reaction, while those of Prevotella loescheii are found to cause coaggregation with other bacteria, i.e., Actinomyces viscosus and sanguis streptococci. Fimbriae from gram-positive oral bacteria such as oral Actinomyces and sanguis streptococci are described. These fimbriae may participate in coaggregation, binding to saliva-coated hydroxyapatite or glycoprotein of the surface layer of oral epithelial cells. Taken together, fimbriae are key components in cell-to-surface and cell-to-cell adherence of oral bacteria and pathogenesis of some oral and systemic diseases.

Virulence factors of Actinobacillus actinomycetemcomitans relevant to the pathogenesis of inflammatory periodontal diseases

There is strong evidence implicating Actinobacillus actinomycetemcomitans as the causative agent of localised juvenile periodontitis (LJP), a disease characterised by rapid destruction of the tooth-supporting tissues. This organism possesses a large number of virulence factors with a wide range of activities which enable it to colonise the oral cavity, invade periodontal tissues, evade host defences, initiate connective tissue destruction and interfere with tissue repair. Adhesion to epithelial and tooth surfaces is dependent on the presence of surface proteins and structures such as microvesicles and fimbriae. Invasion has been demonstrated in vivo and in vitro although the mechanisms involved are poorly understood. The organism has a number of means of evading host defences which include: (i) inhibiting poloymorphonuclear leukocyte (PMN) chemotaxis; (ii) killing PMNs and monocytes; (iii) producing immunosuppressive factors; (iv) secreting proteases capable of cleaving IgG; and (v) producing Fc-binding proteins. Surface components of A. actinomycetemcomitans are potent stimulators of bone resorption and can induce the release of a range of cytokines which can initiate tissue destruction. A number of surface components can also inhibit the proliferation of fibroblasts and their production of components of the extracellular matrix. Little is known, however, regarding the way in which these factors operate in vivo to produce the pathological features of the disease.

An antiserum to a synthetic fimbrial peptide of Actinobacillus actinomycetemcomitans blocked adhesion of the microorganism

The purpose of this study is to certify the importance of the fimbriae as an attachment factor of Actinobacillus actinomycetemcomitans, a human periodontopathic bacterium, and the significance of anti-fimbrial antibody function as an attachment inhibitor. Fimbrial antigen was prepared from the A. actinomycetemcomitans 310-a strain. Oligopeptides were synthesized according to the amino acid sequence of the fimbrial protein. The peptide antigen was conjugated with branched lysine polymer resin beads. The peptide antigen was suspended in PBS emulsified with incomplete Freund's adjuvant and used to immunize rabbits. A rabbit antiserum reacted with an approximately 54 kDa protein of the fimbriae protein from A. actinomycetemcomitans 310-a and with those of other fimbriated strains. This antiserum strongly inhibited the attachment of fimbriated A. actinomycetemcomitans strains to saliva-coated hydroxyapatite beads, buccal epithelial cells, and a fibroblast cell line, Gin-1. Such a synthetic fimbrial peptide antigen may be effective in inducing antibodies which inhibit adhesion and subsequent colonization by A. actinomycetemcomitans.

Adhesion of Actinobacillus actinomycetemcomitans to a human oral cell line

Two quantitative, rapid assays were developed to study the adhesion of Actinobacillus actinomycetemcomitans, an oral bacterium associated with periodontal disease, to human epithelial cells. The human oral carcinoma cell line KB was grown in microtiter plates, and adherent bacteria were detected by an enzyme-linked immunosorbent assay with purified anti-A. actinomycetemcomitans serum and horseradish peroxidase-conjugated secondary antibody or [3H]thymidine-labeled bacteria. Adhesion was found to be time dependent and increased linearly with increasing numbers of bacteria added. Variation in the level of adhesion was noted among strains of A. actinomycetemcomitans. Adhesion was not significantly altered by changes in pH (from pH 5 to 9) but was sensitive to sodium chloride concentrations greater than 0.15 M. Pooled human saliva was inhibitory for adhesion when bacteria were pretreated with saliva before being added to the cells. Pretreatment of the KB cells with saliva did not inhibit adhesion. Protease treatment of A. actinomycetemcomitans reduced adhesion of the bacteria to KB cells. The data are consistent with the hypothesis that a protein(s) is required for bacterial adhesion and that host components may play a role in modulating adhesion to epithelial cells.

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.

Porphyromonas gingivalis invades human pocket epithelium in vitro

The present study examined the adhesive and invasive potential of Porphyromonas gingivalis interacting with human pocket epithelium in vitro. Pocket epithelial tissue, obtained during periodontal surgery of patients with advanced periodontal disease, generated a stratified epithelium in culture. P. gingivalis strains W50 and FDC 381 (laboratory strains), OMGS 712, 1439, 1738, 1739 and 1743 (clinical isolates) as well as Escherichia coli strain HB101 (non-adhering control) were tested with respect to epithelial adhesion and invasion. Adhesion was quantitated by scintillation spectrometry after incubation of radiolabeled bacteria with epithelial cells. The invasive ability of P. gingivalis was measured by means of an antibiotic protection assay. The epithelial multilayers were infected with the test and control strains and subsequently incubated with an antibiotic mixture (metronidazole 0.1 mg/ml and gentamicin 0.5 mg/ml). The number of internalized bacteria surviving the antibiotic treatment was assessed after plating lyzed epithelial cells on culture media. All tested P. gingivalis strains adhered to and entered pocket epithelial cells. However, considerable variation in their adhesive and invasive potential was observed. E. coli strain HB101 did not adhere or invade. Transmission electron microscopy revealed that internalization of P. gingivalis was preceded by formation of microvilli and coated pits on the epithelial cell surfaces. Intracellular bacteria were most frequently surrounded by endosomal membranes; however, bacteria devoid of such membranes were also seen. Release of outer membrane vesicles (blebs) by internalized P. gingivalis was observed. These results support and extend previous work from this laboratory which demonstrated invasion of a human oral epithelial cell-line (KB) by P. gingivalis.

Conjugal transfer of broad-host-range incompatibility group P and Q plasmids from Escherichia coli to Actinobacillus actinomycetemcomitans

The first example of conjugal transfer of DNA from Escherichia coli to the periodontal pathogen Actinobacillus actinomycetemcomitans is presented. Derivatives of the incompatibility group P (IncP) plasmid RK2 successfully transferred from an E. coli donor to an A. actinomycetemcomitans recipient. The resulting A. actinomycetemcomitans transconjugants transferred the plasmids back to E. coli recipients. The IncP transfer functions were also used in trans to mobilize the IncQ plasmid pBK1 from E. coli to A. actinomycetemcomitans. The IncP and IncQ plasmids both transferred into A. actinomycetemcomitans at high frequencies (0.3 to 0.5 transconjugants per donor) and showed no gross deletions, insertions, or rearrangements. Determinations of MICs of various antibiotics for the A. actinomycetemcomitans transconjugant strains demonstrated the expression of ampicillin, chloramphenicol, and kanamycin resistance determinants.

Killing of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus by human polymorphonuclear leukocytes in serum and saliva

The ability of polymorphonuclear leukocytes from human peripheral blood to kill Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus was examined with fresh isolates and laboratory strains from each species (5 strains within each group) under different conditions. Bacterial cells were mixed with a polymorphonuclear leukocyte suspension in the presence of either active serum or heat-inactivated serum or active serum together with sterile-filtered saliva. Surviving bacteria were determined by counting the number of bacterial colony-forming units in the mixtures after a 60-min incubation at 37 degrees C. Mixtures without polymorphonuclear leukocytes served as controls for the evaluation of the degree of killing of the bacteria. In general, A. actinomycetemcomitans resisted phagocytic killing to a greater extent than H. aphrophilus, and the killing of the former species mainly depended on the presence of heat-labile serum components, probably complement factors. Laboratory strains of A. actinomycetemcomitans were more easily killed than fresh isolates. The presence of saliva in the reaction mixtures decreased the degree of killing. However, strain-dependent variations in the killing were found under either condition. The leukotoxic activity of A. actinomycetemcomitans strains, determined by a [51Cr]-release assay, was not correlated with the resistance of these strains to the phagocytic killing. The results point out a strain-dependent difference in the ability of A. actinomycetemcomitans to evade the inflammatory response associated with polymorphonuclear leukocytes. This difference may constitute a potential virulence factor for this periodontopathogen. Furthermore, the leukotoxicity of the strains is not the main determinant that modifies the interaction of A. actinomycetemcomitans with human neutrophils.

Significance of serum antibody against surface antigens of Actinobacillus actinomycetemcomitans in patients with adult periodontitis

This study was undertaken to examine the prevalence of Actinobacillus actinomycetemcomitans, its serotype distribution and the serum immune responses against its surface antigens in 41 Japanese patients with adult periodontitis. The dominant A. actinomycetemcomitans serotype isolated was serotype c. Immunoblot analysis of 3 serotypes of A. actinomycetemcomitans-sonicated antigens and the patient sera revealed that the reactivities with serotype c were the most frequent and that heat-stable surface serotype-specific antigen appeared to be immunodominant. Elevated serum immunoglobulin G titers to extracted lipopolysaccharide and fimbriae antigen of A. actinomycetemcomitans were noted for the patient sera by enzyme-linked immunosorbent assay. High serum immunoglobulin G titers to the fimbriae antigen detected in patients without cultivable A. actinomycetemcomitans suggested the possibility that the elicited antibody to the antigen played a role in eliminating A. actinomycetemcomitans from the periodontal lesions.

Relative avidity of serum immunoglobulin G antibody for the fimbria antigen of Actinobacillus actinomycetemcomitans in patients with adult periodontitis

The relative avidity of serum immunoglobulin G antibody for the fimbria antigen of Actinobacillus actinomycetemcomitans was assessed by diethylamine dissociation enzyme-linked immunosorbent assay in patients with adult periodontitis. High-titer sera from patients not harboring A. actinomycetemcomitans had significantly higher avidities for the fimbria antigen than did high-titer sera from patients with A. actinomycetemcomitans in their periodontal pockets. The elicited antibodies against the fimbria antigen may afford protection against A. actinomycetemcomitans infection.

Entrance of Actinobacillus actinomycetemcomitans into HEp-2 cells in vitro

A strain of actinobacillus actinomycetemcomitans, freshly isolated from a juvenile periodontitis patient, and the FDC Y4 laboratory strain of Aa were tested for their capacity to adhere to and enter the epithelial cell line HEp-2 cells in vitro. Immunofluorescence microscopy as well as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that both strains adhered to the outer surface of the HEp-2 cells. In the TEM studies, the specimens were also treated with Aa specific antibodies and gold labeled protein A. These examinations showed that only the freshly isolated strain of Aa was found within the HEp-2 cells. The intracellular Aa were found to be viable, and in one case one of them was seen to undergo division. It is concluded that freshly isolated Aa has the ability to enter epithelial HEp-2 cells in vitro, and it is tentatively suggested that this may play a role in the pathogenesis of periodontal disease.

Cell surface hydrophobicity and electrokinetic potential of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus

Laboratory strains and fresh isolates of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus were examined for cell surface hydrophobicity and for electrokinetic properties under different experimental conditions. Fresh isolates of A. actinomycetemcomitans and H. aphrophilus were hydrophobic. Laboratory strains of A. actinomycetemcomitans were 20-30% less hydrophobic than fresh isolates. No difference was observed between laboratory and fresh isolates of H. aphrophilus. The pH of the suspending buffer, growth phase or incubation atmosphere did not significantly affect the hydrophobicity of the 2 species, whereas agar cultures of H. aphrophilus were less hydrophobic than broth cultures. All A. actinomycetemcomitans strains treated with sterile filtered saliva showed a concentration-dependent decrease in hydrophobicity of at most 30%. H. aphrophilus strains were not affected by the same treatment. Laboratory strains of H. aphrophilus were more negatively charged than A. actinomycetemcomitans, whereas fresh isolates of the 2 species exhibited similar surface charge. In the presence of saliva the mean cell surface charge of laboratory strains decreased by 56% for A. actinomycetemcomitans and by 73% for H. aphrophilus. The results indicate that the 2 species differ in expression of cell structures accounting for hydrophobicity and surface charge and that environmental factors might differently influence the physical properties of the two species analyzed.

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)

Invasive growth of Actinobacillus actinomycetemcomitans on solid medium (TSBV)

When grown on agar, most Actinobacillus actinomycetemcomitans form circular and convex colonies with an internal star-shaped morphology. Such colonies adhere firmly to the agar, and when removed, a star-shaped imprint similar to that of the intact colony remains. This study was undertaken to determine the nature of this in vitro growth. Stereo-microscopy and scanning and transmission electron microscopy showed that the star-shaped imprint of A. actinomycetemcomitans colonies reflected pseudopod-like extensions of the bacterial colony which penetrated deep into the TSBV agar. The center of the colonies consisted primarily of ghost-like cells, while the dense border of each colony, including the pseudopods, expressed characteristics of vital cells. The latter were embedded in vast amounts of extracellular vesicles, and the outer aspect of the pseudopods was lined with a border of such vesicles.

Plasmids in Actinobacillus actinomycetemcomitans strains isolated from periodontal lesions of patients with rapidly destructive periodontitis

Several strains of Actinobacillus actinomycetemcomitans newly isolated from periodontal lesions of patients with rapidly destructive periodontitis were all shown to possess identical plasmid profiles consisting of 4 plasmids. The largest plasmid, 20 MegaDalton (MDa), was also found in reference strains. Two different methods were used for isolation of the plasmids; the large 20 MDa plasmid (pHRP1) was found using the Kado and Liu method only. The 3 small plasmids of 7.0, 5.2 and 4.0 MDa (pHRP2, pHRP3, pHRP4), respectively, were seen using the Birnboim and Doly method. These plasmids are so far to be regarded as cryptic; no phenotypical characters have been linked to their presence. The large 20 MDa plasmid was found in all strains examined, and may be a genotypical marker for the A. actinomycetemcomitans species.