Chemical and immunological comparison of surface fibrils of strains representing six taxonomic groups of Actinomyces viscosus and Actinomyces naeslundii

Direct detection of cell surface interactive forces of sessile, fimbriated and non-fimbriated Actinomyces spp. using atomic force microscopy

Actinomyces species are predominant early colonizers of the oral cavity and prime mediators of inter-bacterial adhesion and coaggregation. Previous workers have evaluated the adhesion of Actinomyces spp. by quantitative assessment of sessile, as opposed to planktonic cells attached to substrates, but did not quantify the cell surface interactive forces. Therefore we used atomic force microscopy to directly detect the interactive force between an approaching silicon tip and sessile Actinomyces spp. adhering to a substrate, at nanonewton (nN) range force levels. A total of eight strains each belonging to fimbriated and non-fimbriated Actinomyces species were employed, namely A. bovis, A. gerencseriae, A. israelii, A. meyeri, A. naeslundii genospecies 1 and 2, A. odontolyticus and A. viscosus. The sterile mica discs, used as the adhesion substrate, were immersed in mono-species bacterial suspensions for five days to obtain a thin bacterial biofilm. Interactive forces were measured using a silicon nitride cantilever attached to a Nanoscope IIIA atomic force microscope. The interactive forces between the approaching silicon nitride tip and bacterial biofilm surfaces were randomly quantified at three different locations on each cell; namely, the cell surface proper, the periphery of the cell and the substrate and, the interface between two cells. When the interactive forces at these locations of the same species were compared, significantly higher force levels at the cell-cell interface than the other two locations were noted with A. gerencseriae (P < 0.001), A. viscosus (P < 0.01) and A. israelii (P < 0.05). When the interactive forces of different Actinomyces spp. at an identical location were compared, fimbriated A. naeslundii genospecies 2 showed the greatest interactive force at the cell surface proper (-32.6 +/- 8.7 nN, P < 0.01). A. naeslundii genospecies 1, 2 and A. viscosus demonstrated greater interactive force at the cell-mica periphery than the other five species (P < 0.05); A. viscosus (-34.6 +/- 10.5 nN) displayed greater interactive force at the cell-cell interface than the others (P < 0.01), except for A. gerencseriae (P > 0.05). These data indicate that fimbriated Actinomyces spp., including A. naeslundii genospecies 1, 2 and A. viscosus exert higher cell surface interactive forces than those devoid of fimbriae and, such variable force levels may modulate their adhesion and coaggregation during biofilm formation.

Antigenic relationships among oral Actinomyces isolates, Actinomyces naeslundii genospecies 1 and 2, Actinomyces howellii, Actinomyces denticolens, and Actinomyces slackii

Antigenic relatedness among human strains of oral Actinomyces and similar isolates from cattle has been analyzed by agglutination and immunoblotting. Whole cell agglutination placed A. viscosus serotype II, A. naeslundii serotypes II and III, Actinomyces NV, and strains from numerical taxomonic clusters C1, C2, C3, C4, and C6 into a single group. A. viscosus serotype I cross-reacted weakly with this group. A naeslundii serotype I strains and the cattle isolates Actinomyces denticolens and Actinomyces howellii were distinct. The agglutination results for A. slackii were equivocal. Immunoblots of cell wall extracts developed with non-absorbed sera showed cross-reactivity (23% to 90% antigenic similarity) among all of the strains tested, including A. israelii. The range of antigenic similarities among the group which included strains of A. viscosus serotype II, the A. naeslundii serotypes, and clusters C1, C2, C3, C4, and C6 was from 39% to 89%. Immunoblotting showed that A. howellii and A. denticolens were between 39% and 72% similar to A. naeslundii and A. viscosus. Absorption of antisera with A. israelii cell walls removed antibodies recognizing antigens common to Actinomyces and made the sera more specific. Immunoblotting with absorbed sera supported the grouping and separation of strains shown by agglutination. In some cases, serotypes could be included into a specific taxonomic cluster. A. naeslundii serotype II and Actinomyces NV most closely resembled cluster C1 strains, and A. naeslundii serotype III resembled cluster C1 strains, and A. naeslundii serotype I and A. viscosus serotype I were included into clusters C5 and C7, respectively. The results support a recent proposal that strains of A. viscosus serotype II, A. naeslundii serotypes II and III, and Actinomyces NV be included into A. naeslundii genospecies 2, that A. naeslundii serotype I should be designated A. naeslundii genospecies 1, and that A. viscosus serotype I should be retained distinct from A. naeslundii, as A. viscosus.

Actinomyces viscosus fibril antigens detected by immunogold electron microscopy

Strains representing taxonomic clusters of Actinomyces viscosus and Actinomyces naeslundii were studied by indirect immunogold electron microscopy with either monospecific anti-type 1 and anti-type 2 rabbit antibodies or species-specific monoclonal antibodies. The monoclonal and anti-type 2 antibodies localized on long fibrils, whereas the anti-type 1 antibodies mostly localized close to the cell body or on shorter appendages.

Cloning and nucleotide sequence of a gene for Actinomyces naeslundii WVU45 type 2 fimbriae

A genomic library of Actinomyces naeslundii WVU45 DNA in Escherichia coli was screened for antigen expression with rabbit antibody against A. naeslundii fimbriae. Western blotting (immunoblotting) of one recombinant clone carrying a 13.8-kilobase-pair insert revealed a 59-kilodalton (kDa) immunoreactive protein. A protein of similar electrophoretic mobility was detected from the isolated fimbrial antigen. Expression of the 59-kDa cloned protein in E. coli was directed by a promoter from the insert. The DNA sequence of the subunit gene was determined, and an open reading frame of 1,605 nucleotides was identified which was preceded by a putative ribosome-binding site and followed by two inverted repeats of 14 and 17 nucleotides, respectively. The reading frame encoded a protein of 534 amino acids (calculated molecular weight, 57,074), and the N-terminal sequence resembled that of a signal peptide. The presence of a 32-amino-acid signal peptide was indicated by amino-terminal sequencing of the fimbriae from A. naeslundii. The sequence, as determined by Edman degradation, was identical to that deduced from the DNA sequence beginning at predicted residue 33 of the latter sequence. Moreover, the amino acid composition of the predicted mature protein was similar to that of the isolated fimbriae from A. naeslundii. Thus, the cloned gene encodes a subunit of A. naeslundii fimbriae.

Distribution of antigenic determinants between Actinomyces viscosus and Actinomyces naeslundii

A total of 18 monoclonal antibodies was raised against whole cells of Actinomyces viscosus and Actinomyces naeslundii. The monoclonal antibodies were used to determine the cross-reacting patterns among 26 strains of these species. Eleven different antigenic determinants were found. The specificity profiles of the antibodies indicated that the antigenic determinants of A. viscosus and A. naeslundii were arranged in a complicated mosaic. Extensive cross-reactions occurred between A. viscosus strains and strains of "typical" and "atypical" A. naeslundii. However, cross-reactions were rare between the two groups of A. naeslundii. A. viscosus appears to occupy a "middle position" between the two A. naeslundii groups. In addition to their value in seroclassification, some of the monoclonal antibodies were found to be useful in the identification of these species. One monoclonal antibody appeared to be selective for the "typical" A. naeslundii group. A. viscosus and "atypical" A. naeslundii-specific antibodies were also found, though they did not label every strain in their respective clusters. A. viscosus detection might be improved if mixtures of monoclonal antibodies were used.

Fluctuations in crevicular and salivary anti-A. viscosus antibody levels in response to treatment of gingivitis

Experimental gingivitis studies support a pathogenic rôle for Actinomyces viscosus because of its numerical predominance in disease-associated plaques. The aims of the present investigation were to quantify specific crevicular IgG against A. viscosus before and after conventional gingivitis treatment and to determine whether salivary IgA and IgG against A. viscosus and A. naeslundii would be affected concomitantly. 6 subjects with generalized gingivitis were selected. Examinations were made before and after treatment and included collection of unstimulated saliva, paraffin-stimulated saliva and crevicular material as well as measurements of clinical parameters. The immunoglobulins were estimated by an ELISA assay using whole bacterial cells as antigen. Crevicular IgG against A. viscosus WVU 627 was demonstrated in pre- and post-treatment samples with a tendency towards increased values in the post-treatment samples. Salivary IgA and IgG against A. viscosus were also demonstrated in pre- and post-treatment samples. There were tendencies towards increased IgA values for paraffin-stimulated saliva and increased IgG values for unstimulated saliva in the post-treatment samples. Salivary IgA and IgG values against A. naeslundii ATCC 12104 were either not detected or barely detectable in both pre- and post-treatment samples. A. naeslundii B 74 IgG values were also rather low. As for A. viscosus WVU 627, anti-B 74 IgA values demonstrated a post-treatment increase for most subjects, especially for unstimulated saliva for which all post-treatment values were elevated. It is interesting to note that saliva samples showed changes similar to crevicular material, considering that salivary IgA is most likely derived from a different source. Together, elevated crevicular and salivary antibody concentrations might account for some of the beneficial effects of periodontal therapy by scaling.

Expression of Actinomyces viscosus antigens in Escherichia coli: cloning of a structural gene (fimA) for type 2 fimbriae

A cosmid gene library of Actinomyces viscosus T14V was prepared in Escherichia coli to examine the expression of A. viscosus antigens and to gain insight into the structure of A. viscosus type 1 and type 2 fimbriae. Out of this library of 550 clones, 28 reacted in a colony immunoassay with antibodies against A. viscosus cells. The proteins responsible for these reactions were identified in three clones. Clones AV1209 and AV2009 displayed nonfimbrial antigens with subunits of 40 and 58 kilodaltons, respectively. Clone AV1402 showed a 59-kilodalton protein that reacted with monospecific antibody against type 2 fimbriae and that comigrated with a subunit of type 2 fimbriae during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This indicates that AV1402 expresses a gene (fimA) for a subunit of A. viscosus type 2 fimbriae.

Assignment of Actinomyces viscosus and Actinomyces naeslundii strains to numerical taxonomy clusters by immunofluorescence based on antifibril antisera

A previous observation, using a few representative laboratory strains, that rabbit antisera raised against isolated surface fibrils might be useful in identifying Actinomyces viscosus and Actinomyces naeslundii isolates to their correct numerical taxonomy clusters was reexamined with a large culture collection, including clinical isolates from three different laboratories. Strains were first identified by a slower standard procedure, including agglutination with anti-whole-cell antisera, catalase test, and gas and paper chromatography as needed. Indirect immunofluorescence tests indicated that antisera raised against fibrils of strains representing the three principal taxonomic clusters could separate most strains into their correct clusters. The antisera were particularly successful in separating two taxonomically distinct groups of A. naeslundii, clusters 3 and 5, but could not separate A. viscosus belonging to the principal cluster (no. 1) and minor clusters (no. 2, 4, 6).

Exclusive presence of lactose-sensitive fimbriae on a typical strain (WVU45) of Actinomyces naeslundii

Lactose-sensitive fimbriae were identified as the only fimbriae present on Actinomyces naeslundii WVU45 (ATCC 12104). A single antigen reactive with antiserum against WVU45 cells was detected by cross immunoelectrophoresis of isolated fimbriae, and a monospecific antiserum against this antigen reacted with all fimbriae observed on the bacterial surface by immunoelectron microscopy. Moreover, the loss of one cell surface antigen by a spontaneous mutant of A. naeslundii WVU45 (WVU45M), isolated by its failure to react with a monospecific antibody against the fimbriae, was associated with the loss of all fimbriae. The functional involvement of the fimbriae in lactose-sensitive bacterial adherence was demonstrated by the ability of WVU45, but not WVU45M, cells to agglutinate neuraminidase-treated erythrocytes and by the lactose-sensitive hemagglutinating activity of immune complexes formed with isolated fimbriae and monospecific antibody. Bacterial agglutination assays with different monospecific antibodies revealed an antigenic similarity between the fimbriae of A. naeslundii WVU45 and the lactose-sensitive fimbriae (type 2) of Actinomyces viscosus T14V. In contrast, cross-reactivity was not observed between the WVU45 fimbriae and type 1 fimbriae, the structures involved in lactose-resistant adherence of strain T14V to saliva-treated hydroxyapatite. Functional differences between the fimbriae of A. naeslundii and A. viscosus strains may be correlated with well-established differences in the in vivo distribution of these organisms: namely, the preference of typical A. naeslundii for epithelial surfaces and of A. viscosus for tooth surfaces.

Structural preferences of beta-galactoside-reactive lectins on Actinomyces viscosus T14V and Actinomyces naeslundii WVU45

Specificities of lectins on Actinomyces viscosus T14V and Actinomyces naeslundii WVU45 were compared by measuring the abilities of D-galactose, N-acetyl-D-galactosamine, 14 beta-D-galacto-oligosaccharides, and 2 beta-D-fuco-oligosaccharides to inhibit coaggregation between Streptococcus sanguis 34 and each actinomycete. Inhibition profiles were similar, but WVU45 was significantly more sensitive to several inhibitors. D-Galactose-beta(1 leads to 3)-N-acetyl-D-galactosamine glycosides were most potent.

Actinomyces viscosus and Actinomyces naeslundii agglutinins in human saliva

The objectives were to determine the degree of Actinomyces agglutinating activity in human saliva and to begin characterizing the agglutination mechanism. Agglutination titres of whole saliva collected from adults and 6-yr-old children were compared. Titres for A. naeslundii were always higher than for A. viscosus. The mean A. naeslundii titre for the adults' and children's samples were equivalent. The children had a slightly lower mean titre than the adults for A. viscosus. No correlation was found between IgA concentrations and agglutination titre. Agglutinating activity was partially impaired by incubation with anti-IgA serum. Activity in submandibular/sublingual saliva was resistant to heat at 56 degrees C but sensitive to boiling. Boiling the bacteria had no effect. In sugar inhibition tests, only galactosides (beta-Gal) and glucosamine (for A. viscosus) affected Actinomyces agglutination but impairment was only temporary. Agglutinating activity was diminished by incubating saliva with hydroxyapatite. Thus, Actinomyces agglutinins 1) are probably distinct from IgA but may complex with it; 2) may include both beta-Gal and higher affinity sites; and 3) may contribute to salivary pellicle.