Identification and characterization of the major cell envelope proteins of oral strains of Actinobacillus actinomycetemcomitans

Altered antigenicity is seen in the lipopolysaccharide profile of non-serotypeable Actinobacillus actinomycetemcomitans strains

Non-serotypeable Actinobacillus actinomycetemcomitans strains may be derived from the serotypeable ones. In the present study, we compared the outer membrane proteins (OMPs) and lipopolysaccharides (LPSs) of serotypeable and non-serotypeable A. actinomycetemcomitans strains (n=24) of the same genotype in the same subject (n=6) to find out if alterations on the cell-surface contribute to the non-serotypeability. Serotypeable and non-serotypeable A. actinomycetemcomitans strains showed great similarity in the OMP patterns both within and between subjects. Using serotype-specific antisera, clear immunoblotting LPS profiles in the O-antigenic region were seen in serotype b and c strains but not in non-serotypeable strains from the same subjects. The results suggest that changes in LPS lead to the altered antigenicity of non-serotypeable A. actinomycetemcomitans strains.

Subcellular localization and cytotoxic activity of the GroEL-like protein isolated from Actinobacillus actinomycetemcomitans

The subcellular locations, ultrastructure, and cytotoxic activity of the GroEL-like protein from Actinobacillus actinomycetemcomitans were investigated. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) clearly indicated that synthesis of the GroEL-like protein is substantially increased after a thermal shock. Analysis of the purified native GroEL-like protein by transmission electron microscopy revealed the typical 14-mer cylindrical molecule, which had a diameter of about 12 nm. A. actinomycetemcomitans cells grown at 35 degreesC and heat shocked at 43 degreesC were fractionated, and fractions were separated by SDS-PAGE and analyzed by Western immunoblotting using antibodies to GroEL- and DnaK-like proteins. The GroEL-like protein was found in both the soluble and membrane fractions, whereas the DnaK-like protein was mostly found in the cytoplasm. An increase in specific proteins, including the GroEL- and DnaK-like proteins, was found in heat-shocked cells. The subcellular localization of the GroEL-like protein was examined by immunoelectron microscopy of whole cells. More GroEL-like protein was detected in stressed cells than in unstressed cells, and most of it was found not directly associated with outer membranes but rather in extracellular material. The native GroEL-like protein was assessed for cytotoxic activities. The GroEL-like protein increased the proliferation of periodontal ligament epithelial cells at concentrations between 0.4 and 1.0 microgram/ml. The number of cells in the culture decreased significantly at higher concentrations. A cell viability assay using HaCaT epithelial cells indicated that the GroEL-like protein was strongly toxic for the cells. These studies suggest the extracellular nature of the GroEL-like protein and its putative role in disease initiation.

Antigenic diversity in the periodontopathogen, Actinobacillus actinomycetemcomitans

We have identified a significant level of variation in antibody responses to Actinobacillus actinomycetemcomitans outer membrane antigens (OMA). This study was designed to verify A. actinomycetemcomitans antigenic diversity that could contribute to maintaining this chronic infection despite the host immune response. A. actinomycetemcomitans strains (5 from different patients and 3 the same patient) were cultured and OMA prepared for Western immunoblotting studies. Antigen bands in the OMA were identified using 7 sera obtained from 3 adult periodontitis (AP) and 4 localized juvenile periodontitis (LJP) patients that were documented with elevated A. actinomycetemcomitans antibody and infection. Differences/similarities in the antigen patterns among the A. actinomycetemcomitans strains were assessed using a kappa similarity coefficient. Antigen bands in the A. actinomycetemcomitans strains ranged from 11-150 kDa; however, variation in antigen patterns were noted among the strains. Utilizing the human sera as probes for antigenic diversity, the 5 heterologous strains showed average K=0.23 (p < 0.05), while homologous A. actinomycetemcomitans strains had a K=0.48 (p < 0.02). The A. actinomycetemcomitans OMA were used as probes to describe variability in host antibody and as such presumptive evidence of antigenic diversity in A. actinomycetemcomitans that is colonizing each of the patients. The results showed average K=0.26 (p < 0.05) for the patients when tested against each of the heterologous strains, and K=0.14 when tested against the homologous strains (p > 0.1). Finally, antigen bands of M r 80, 65, 58, 31 and 20 kDa were demonstrated as antigens contributing to the antigenic diversity in A. actinomycetemcomitans.

Antigen specificity of serum antibody in A. actinomycetemcomitans-infected periodontitis patients

We hypothesized that serum antibody with selected antigen specificities would relate to infection and disease in the patients and, thus, describe the characteristics of potential protective antibody. This study used serum samples from 24 periodontitis patients with subgingival infection and elevated serum IgG antibody to A. actinomycetemcomitans to define the antigenic specificities of IgG, IgM, IgA, and IgG1-4 antibody to A. actinomycetemcomitans strain Y4 outer membrane antigens (OMA). Uniform IgG antibody (> 70% of the patients) was noted to antigens with M(r) of 65, 38, 29, and 17 kDa. Both IgA and IgM specificities reflected those shown for IgG in each patient. IgG1 and IgG2 antibody reacted with several OMA bands in each patient, while IgG3 antibodies were directed to numerous OMA bands in many patients and represented the most broad-based response. The IgG4 response patterns were limited to a few OMA bands. We noted a prominent occurrence of IgG reactions with OMA bands that were characteristic for individual patients. The frequency of responses to OMA of higher M(r) (i.e., > 80 kDa) and to the 34-, 31-, and 24-kDa antigens was positively related to the total IgG antibody levels. Antibody reactive with OMA bands at 65-, 38-, 29-, 17-, 15-, and 11-kDa antigens was detected in patients with few to many teeth infected with A. actinomycetemcomitans. Furthermore, patients with a high percentage of teeth with > or = 6 mm pockets had a decreased frequency of responses to the high-M(r) antigens (i.e. > 90 kDa) as well as to the 58-kDa antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

Lactoferrin interaction with Actinobacillus actinomycetemcomitans

The interaction of lactoferrin with Actinobacillus actinomycetemcomitans was examined in a 125I-labeled protein binding assay. The binding of human and bovine lactoferrins reached maximum within 1 h. Lactoferrin binding to the bacterium was pH-dependent and reversible. Scatchard analysis indicated the existence of two different types of binding sites on the bacterium, one with a high affinity constant k alpha approximately 8.8 x 10(-7) M) and the other with a low one (k alpha approximately 1.8 x 10(-6) M). Bacteria in the exponential phase of growth showed higher binding than cells in the stationary phase. Bacteria grown in medium containing serum and/or lysed erythrocytes bound lactoferrin to a lesser extent. Heat-inactivated serum, lysed erythrocytes and other proteins such as mucin and laminin inhibited lactoferrin binding to A. actinomycetemcomitans in a competitive binding assay. Sodium dodecyl sulfate polyacrylamide-gel electrophoresis and Western blot analysis of the cell envelope as well as the outer membrane of A. actinomycetemcomitans revealed lactoferrin-reactive protein bands at 29 kDa and 16.5 kDa. The 29-kDa band displayed a heat-modifiable lactoferrin-reactive form with a molecular weight of 34 kDa. Neither proteinase K-treated cell envelope nor lipopolysaccharide of this bacterium showed reactivity with lactoferrin. These data suggests a specific interaction of lactoferrin with outer membrane proteins of A. actinomycetemcomitans.

Comparison of six typing methods for Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans is an important pathogen in the etiology of severe periodontitis. For epidemiological studies on the prevalence of certain pathogenic clones and transmission of this bacterium, adequate typing methods are necessary. The purpose of this study was to compare six different typing methods for A. actinomycetemcomitans. Five reference strains and 27 fresh clinical isolates from periodontitis patients were used. Serotyping showed 12 serotype a strains, 13 type b strains, 6 type c strains, and 1 nontypeable strain. Biotyping on the basis of the fermentation of mannose, mannitol, and xylose resulted in six biotypes. Antibiogram typing was evaluated by measuring the inhibition zones of seven antibiotics in agar diffusion tests. With this method eight main types which could be further differentiated into 15 subtypes were found. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of outer membrane proteins were similar among all isolates tested. Restriction endonuclease analysis (REA) of whole chromosomal DNA resulted in five main types. These five main types were further differentiated into 24 subtypes on the basis of DNA fragment differences in the high-molecular-weight region. Hybridization of DNA fragments with ribosomal DNA (ribotyping) resulted in 22 to 24 different types, depending on the restriction endonuclease used. Ribotype patterns were easy to interpret and provided an univocal distinction between different strains compared with REA results. When applied to epidemiologically related isolates, all methods were able to discriminate two clonal types among five isolates from five children from one family. We conclude that serotyping, biotyping, and outer membrane patterns were reproducible but had a low discriminatory potential. REA and ribotyping were reproducible and gave the highest number of distinct types. When the DNA typing methodis were compared, all strains tested could be distinguished. These findings confirm the heterogeneity found within the species A. actinomycetemcomitans.

Recent approaches to the chemotaxonomy of the Actinobacillus-Haemophilus-Pasteurella group (family Pasteurellaceae)

Many members of the Actinobacillus-Haemophilus-Pasteurella group (family Pasteurellaceae) have been misclassified. This article reviews the chemotaxonomic characters that recently have been provided to improve the taxonomy of Pasteurellaceae. These include fatty acids of whole cells, of lipopolysaccharides and of single colonies, together with sugar contents of whole cells, of whole defatted cells, of lipopolysaccharides and of single colonies. This article also reviews taxonomy aided by distribution of proteins in whole cells and outer membranes, distribution of enzymes in outer membrane vesicles and in whole cells, bacteriolysis induced by ethylenediaminetetraacetic acid and hen eggwhite lysozyme and the distribution of respiratory quinones. Furthermore, an overview of characters obtained through studies on genetic transformation, restriction enzyme analysis, restriction fragment length polymorphism, DNA-DNA hybridization, DNA-rRNA hybridization, and 16S rRNA sequencing is given.

Identification of genomic clonal types of Actinobacillus actinomycetemcomitans by restriction endonuclease analysis

To evaluate its utility in discriminating different strains, restriction endonuclease analysis was applied to 12 strains of Actinobacillus actinomycetemcomitans (3 serotype a, 5 serotype b, and 4 serotype c strains). DNA isolated from each strain was digested by 12 different restriction endonucleases, and the electrophoretic banding patterns of the resulting DNA fragments were compared. The DNA fragment patterns produced by SalI, XhoI, and XbaI for the 12 A. actinomycetemcomitans strains were simple (less than 30 bands) and allowed us to recognize easily 10 distinct genomic clonal types. The three serotype a strains exhibited distinctly different clonal types from one another, the five serotype b strains exhibited an additional four distinct clonal types, and the four serotype c strains showed another three different clonal types. The other endonucleases tested were less useful in typing A. actinomycetemcomitans. We conclude that restriction endonuclease analysis is a powerful tool for typing and discerning genetic heterogeneity and homogeneity among A. actinomycetemcomitans strains. It should, therefore, be very useful for epidemiologic studies.

The heat-modifiable outer membrane protein of Actinobacillus actinomycetemcomitans: relationship to OmpA proteins

The outer membrane of Actinobacillus actinomycetemcomitans contains a 29-kDa protein which exhibits heat modifiability on sodium dodecyl sulfate-polyacrylamide gels and represents a major target for immunoglobulin G antibody in sera of periodontitis patients colonized by this organism. In the present study, the N-terminal amino acid sequence of the 29-kDa outer membrane protein was determined and compared with reported sequences for other known proteins. The heat-modifiable outer membrane protein of A. actinomycetemcomitans was found to exhibit significant N-terminal homology with the OmpA proteins of other gram-negative bacteria. Moreover, this protein reacted with antiserum raised against the purified OmpA protein of Escherichia coli K-12. Whether the heat-modifiable OMP of A. actinomycetemcomitans also shares functional properties of OmpA proteins, particularly with respect to bacteriophage receptor activity, is presently under investigation.

Use of randomly cloned DNA fragments for the identification of oral spirochetes

DNA probes were produced for the detection and identification of 4 cultivable species of oral spirochetes, Treponema denticola, Treponema socranskii, Treponema vincentii and Treponema pectinovorum. To obtain probe sequences, chromosomal DNA, isolated from representative strains within each species, was cloned in Escherichia coli K-12. Cloned DNA fragments were screened for the ability to hybridize to DNA only from homologous strains. Several such fragments were identified and shown to be specific when tested against a series of DNAs from gram-negative and gram-positive oral bacteria. The selected probe sequences were semi-conserved within strains of T. denticola and T. socranskii such that restriction fragment length polymorphism (RFLP) was observed. In the case of T. socranskii, RFLP was useful in distinguishing between the 3 known subspecies. Chromosomal DNA fragments from 2 strains of T. vincentii failed to cross-hybridize, under stringent conditions, to genomic DNA from each of these strains. The hybridization probes were suitable for the identification of clinical isolates of T. denticola and could be used to detect the presence of individual Treponema species in mixed cultures. On this basis, the probes were used successfully to detect T. denticola in uncultured plaque samples.

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)

Antigens of Actinobacillus actinomycetemcomitans recognized by patients with juvenile periodontitis and periodontally normal subjects

Most juvenile periodontitis patients respond to infection by Actinobacillus actinomycetemcomitans by producing serum antibodies. Specific antigens inducing the humoral immune response have not been identified, nor has the role of the resulting antibodies in disease progression been determined. Adsorbed and unadsorbed sera from juvenile periodontitis patients and normal subjects were analyzed by enzyme-linked immunosorbent assay and Western blots (immunoblots), using digested and undigested bacterial sonicates and French pressure cell fractions to determine the biochemical class, cross-reactivity, and cellular location of the antigens in different A. actinomycetemcomitans serotypes. Antigens detected by using high-titer sera included the following: (i) serotype-specific nonprotein material located on the cell surface, (ii) soluble-fraction proteins showing highly variable antibody binding, (iii) cross-reactive proteins, and (iv) a protein present in soluble and cell wall fractions and immunopositive for all sera tested. In addition, one apparently nonprotein component that was enriched in the cell wall fraction was observed. Sera with high immunoglobulin G titers to one, two, three, or none of the three A. actinomycetemcomitans serotypes were observed. There was a high degree of variation from one patient to another in the humoral immune response to serotype-specific and cross-reactive antigens. As demonstrated by whole-cell adsorption experiments, the serotype-specific surface antigen accounted for approximately 72 to 90% of the total antibody-binding activity for sera with titers greater than 100-fold above background, while cross-reactive antigen accounted for less than 28%. Antibody binding the whole-cell sonicate for high-titer sera was inhibited 90% by lipopolysaccharide from the same serotype, strongly suggesting that lipopolysaccharide is the immunodominant antigen class.

IgG antibody response of localized juvenile periodontitis patients to the 29 kilodalton outer membrane protein of Actinobacillus actinomycetemcomitans

Levels of serum IgG antibody to the 29 kilodalton outer membrane protein of A. actinomycetemcomitans Y4 in sera of periodontally healthy subjects and localized juvenile periodontitis patients were determined using an enzyme-linked immunosorbent assay (ELISA). The 29 kDa protein was isolated by solubilization of an octylglucoside-NaCl insoluble fraction by incubation at ambient temperature in 20 mM sodium phosphate, pH 7.5, containing 1% sodium dodecyl sulfate. The isolated protein migrated on SDS-polyacrylamide gels with an apparent molecular mass of 29 kDa following incubation in sample buffer at ambient temperature. However, the protein migrated with an apparent molecular mass of 34 kDa following incubation in sample buffer at 100 degrees C for 10 minutes. Geometric mean IgG antibody titers to the 29 kDa protein were significantly higher in sera from LJP subjects than in sera obtained from periodontally healthy subjects. Twenty-two of 35 LJP sera (63%) had antibody titers greater than 2 standard deviations from the mean titer of the periodontally healthy group. Among LJP subjects, elevated antibody titers to the 29 kDa protein were found primarily in subjects greater than or equal to 18 years of age, with the highest titers seen in patients 18 to 21 years of age. The results of this study indicate that the humoral response of LJP subjects to A. actinomycetemcomitans includes the production of IgG antibodies which recognize the major outer membrane proteins of this organism.

Characterization of outer membrane proteins from Actinobacillus actinomycetemcomitans

Outer membranes were prepared from whole cells of various strains of Actinobacillus actinomycetemcomitans and analysed by SDS-polyacrylamide gel (12.5%) electrophoresis (SDS-PAGE). In all strains four common major outer membrane proteins (OMPs) with molecular masses of 30, 34, 36 and 39 kDa could be distinguished. Heating the OMP preparation of strain Y4 at 60, 70, 90 and 100 degrees C produced a band of 30 kDa, which gradually lost its intensity from 70 degrees C onwards concomitantly with the development of two new protein bands of 34 and 36 kDa. Furthermore, the 36 kDa OMP appeared susceptible to proteolysis by trypsin; degraded products apparently produced a new electrophoretic band of 27 kDa. Y4-derived OMP fractions were solubilized with a Triton-SDS mixture to investigate the presence of peptidoglycan-associated proteins. The 39 kDa OMP was found to be peptidoglycan-associated.

Outer membrane proteins of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus studied by SDS-PAGE and immunoblotting

This investigation characterized and compared outer membrane proteins (OMP) of the closely related Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus by means of SDS-PAGE patterns and reactions on immunoblots with rabbit antiserum against A. actinomycetemcomitans FDC Y4. Reactions with serum from a patient with Papillon Lefévre syndrome (PLS), from whom periodontal wild strains of A. actinomycetemcomitans had been isolated, were also studied. OMP were purified with selective solubilization from lyophilized cells of 10 wild and 4 reference strains of A. actinomycetemcomitans and 4 reference strains of H. aphrophilus. OMP profiles from wild and reference strains of A. actinomycetemcomitans were similar while those from A. actinomycetemcomitans and H. aphrophilus differed. The most prominent difference was absence of a heat modifiable protein in H. aphrophilus strains. Immunoblotting revealed strong common antigens in most strains, including a heat modifiable protein with mol wt 34 kDa, as well as a 29 kDa and a 16.5 kDa protein. Treatment with pronase and sodium periodate confirmed the protein nature of the major OMP antigens.

Probe-specific DNA fingerprinting applied to the epidemiology of localized juvenile periodontitis

Although Actinobacillus actinomycetemcomitans has been recognized as a primary etiological agent in localized juvenile periodontitis, questions remain concerning the source of infection, mode of transmission, and relative virulence of strains. DNA fingerprinting analysis, using a randomly cloned chromosomal DNA fragment as a probe, revealed that previously characterized strains of A. actinomycetemcomitans displayed significant restriction site heterogeneity which could be applied to the typing of clinical isolates of this bacterium such that individual strains or variants could be traced within subjects from localized juvenile periodontitis families. Hybridization data derived from an analysis of bacterial isolates obtained from families participating in an ongoing longitudinal study of the disease showed that a single individual could be infected with more than one strain or variant of A. actinomycetemcomitans and that various members of the same family could harbor different strains or variants of the bacterium. In several cases the clinical isolates were matched to characterized laboratory strains by comparing hybridization patterns generated by digestion of the DNA with several restriction enzymes in independent reactions. Thus, probe-specific DNA fingerprinting of A. actinomycetemcomitans will permit us to determine if particular strains or variants are frequently associated with sites of periodontal destruction. Attention could then be focused on determining the virulence properties of those strains or variants that have in vivo significance.

Gene cloning of an Actinobacillus actinomycetemcomitans Y4 antigen which reacts with peripheral blood sera in patients with advanced destructive periodontitis

Actinobacillus actinomycetemcomitans has been implicated in the aetiology of juvenile periodontitis and advanced destructive periodontitis. Levels of IgG antibody against A. actinomycetemcomitans in peripheral blood sera of patients with advanced destructive periodontitis are high, as are those against Bacteroides gingivalis. To clone the genes of antigens reactive with sera of such patients, a library of the A. actinomycetemcomitans strain Y4 DNA in lambda L47 was constructed and then screened, using an immunochemical detection method, with serum from a patient with the advanced disease. Six clones from among nearly 1000 reacted with the serum and also with that of another patient. They were designated 3, 4, 6, 7, 8 and 9. Restriction enzyme and Southern blot analyses indicated that clones 8 and 9 were identical and that all the clones were overlapping because they shared in common the 4 and 5 kbp HincII DNA fragments of A. actinomycetemcomitans. The cloned DNA fragment hybridized to the DNA of two other strains of A. actinomycetemcomitans but not to those of six periodontopathic bacteria examined. These findings suggest that a DNA sequence encoding an A. actinomycetemcomitans strain Y4 antigen strongly reactive with sera of patients with advanced destructive periodontitis was cloned. This sequence is present specifically in A. actinomycetemcomitans but not in other bacteria isolated from patients with periodontal diseases. Thus, the cloned DNA could serve as a probe for the diagnosis of periodontitis.

Intra-oral colonization of macaque monkeys by Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans was acquired by captive Macaca fascicularis 3 to 6 months after birth, and all monkeys aged over 6 months harbored detectable levels. This microorganism was most frequently isolated from the gingival plaque of the incisor (and other) teeth compared with other oral sites. Strains were leukotoxic by bioassay and Western blot analysis. Antibodies in macaque serum contained neutralized the leukotoxin of a human A. actinomycetemcomitans strain. High titres of maternal neutralizing anti-leukotoxin antibodies were detected in neonates; the titre then fell rapidly so that by 6 months the antibody titer was zero. Antileukotoxin antibody production was detected after 6 months of age, rapidly reaching a high level within 2 years after birth. The presence of leukotoxic strains of A. actinomycetemcomitans in the gingival region did not appear to be correlated with an increase in susceptibility to periodontal disease.

Iron-regulated outer membrane protein OM2 of Vibrio anguillarum is encoded by virulence plasmid pJM1

Vibrio anguillarum 775 harboring the virulence plasmid pJM1 synthesized an outer membrane protein of 86 kilodaltons, OM2, that was inducible under conditions of iron limitation. pJM1 DNA fragments obtained by digestion with restriction endonucleases were cloned into cosmid vectors and transferred into Escherichia coli. The OM2 protein was synthesized in E. coli, demonstrating that it is actually encoded by the pJM1 plasmid. Mobilization of the recombinant plasmids to V. anguillarum was accomplished by using the transfer factor pRK2013. A V. anguillarum exconjugant harboring the recombinant derivative pJHC-T7 and synthesizing the OM2 protein took up 55Fe3+ and grew under iron-limiting conditions, only in presence of the pJM1-mediated siderophore. Exconjugants harboring recombinant plasmids, such as pJHC-T2 which did not encode the OM2 protein, were transport negative. Membrane protein iodination experiments, together with protease treatment of whole cells, indicated that the OM2 protein is exposed to the outside environment of the V. anguillarum cells.

Monoclonal antibodies to leukotoxin of Actinobacillus actinomycetemcomitans

Hybridoma cell lines which produce monoclonal antibodies to a leukotoxin from Actinobacillus actinomycetemcomitans were prepared. The monoclonal antibodies were selected for their ability to neutralize the cytotoxic activity of the leukotoxin and recognize the toxin on nitrocellulose blots. The antibodies belonged to either the immunoglobulin G1 (IgG1) or IgG2 subclass and differed in their ability to bind to the leukotoxin on nitrocellulose blots. However, only slight differences in neutralization titers were observed. Use of the monoclonal antibodies revealed that polymyxin B-extracted or osmotic shock-released leukotoxin could be separated into several high-molecular-weight polypeptides by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Immunoblot analysis with the monoclonal antibodies also demonstrated that the leukotoxin was present in eight oral strains of A. actinomycetemcomitans that had been previously classified by a biological assay as leukotoxic. The availability of these monoclonal antibodies should facilitate and expand studies concerning the role of the leukotoxin in the pathogenicity of A. actinomycetemcomitans.

Cell surface proteins of oral streptococci

Whole cells of representative strains of oral streptococci (Streptococcus sanguis, S. mitis, and S. salivarius) were radiolabeled by the lactoperoxidase method of radioiodination. The labeled polypeptides obtained by extraction of whole cells with boiling sodium dodecyl sulfate were analyzed by polyacrylamide gel electrophoresis and autoradiography. Of the total radioactivity, ca. 70% was released by treating whole cells with trypsin, suggesting that the labeling was confined to proteins located on the cell surface. Most S. sanguis strains studied gave a characteristic banding pattern consisting of a high-molecular-weight (120,000 [120K] to 63K) group of six proteins. Three low-molecular-weight (12K, 16K, and 18K) proteins were also detected in many strains.

Isolation of a major cell envelope protein from Fusobacterium nucleatum

A major, heat-modifiable cell envelope protein was identified in Fusobacterium nucleatum FDC 364 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This protein, designated HM-1, had apparent molecular weights of 38,500 and 50,000 when heated in sodium dodecyl sulfate at 50 and 100 degrees C, respectively. Whole cells were labeled with 125I, and the results suggested that the HM-1 protein may be exposed on the bacterial surface. The HM-1 protein was isolated in association with the peptidoglycan by extraction of whole cells or cell envelopes with 2% sodium dodecyl sulfate at 55 degrees C. Heating the peptidoglycan-HM-1 protein complex in the detergent at 100 degrees C resulted in the quantitative release of the protein. Isoelectric focusing experiments and amino acid analysis revealed that the HM-1 protein had a basic character and was moderately hydrophilic. Various strains of F. nucleatum as well as three oral fusiform isolates contained a serologically related protein. The abundance and location of the HM-1 protein in F. nucleatum suggest that it has the potential to participate in cell surface-related interactions of this bacterium.

Extraction and isolation of a leukotoxin from Actinobacillus actinomycetemcomitans with polymyxin B

A leukotoxin from Actinobacillus actinomycetemcomitans was isolated by a procedure that includes polymyxin B extraction, ion-exchange chromatography, and gel filtration chromatography. The procedure resulted in the recovery of 48% of the toxin with a 99-fold increase in specific activity. The isolated toxin has a molecular mass of 180,000 daltons by gel filtration and 115,000 daltons by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It retains all the major biological characteristics previously documented for crude leukotoxin preparations, including susceptibility to heat and proteolytic enzymes and neutralization by sera from patients with juvenile periodontitis. The isolated leukotoxin destroys human but not rat or guinea pig polymorphonuclear leukocytes and has no apparent effect on human erythrocytes. The availability of the A. actinomycetemcomitans leukotoxin should facilitate studies on its chemistry and mode of action as well as its role in the pathogenesis of human periodontal disease.