Characterization of the lipopolysaccharide from Actinobacillus actinomycetemcomitans Y4 and N27

Current concepts in periodontal diseases

Periodontal diseases are common oral diseases that afflict all humans to some degree. The major aetiological agent is dental plaque--the complex microflora which forms on teeth in the absence of effective oral hygiene. The interaction of the microbial flora and the periodontal tissues produces an inflammatory response and tissue breakdown. Recent information has categorized periodontal diseases on the basis of increased knowledge about the particular microorganisms associated with the different clinical conditions. In addition, the important role of host defences, in particular the phagocytic cellular elements, has allowed for a better understanding of the pathological processes. This knowledge is contributing towards the development of rational and effective therapy for all forms of periodontal diseases. Because of the widespread occurrence of periodontal diseases and their potential relationships to systemic conditions, it is important that medical practitioners should be able to recognize, and be conversant with methods of treatment of, these diseases.

Rapid identification of periodontal pathogens in subgingival plaque: comparison of indirect immunofluorescence microscopy with bacterial culture for detection of Actinobacillus actinomycetemcomitans

The sensitivity of indirect immunofluorescence microscopy using specific polyclonal or monoclonal serodiagnostic reagents for Actinobacillus actinomycetemcomitans in subgingival dental plaque ranged from 82-100% as compared with culture on selective or non-selective media. This bacterium was found in 100% of the periodontally diseased sites examined in localized juvenile periodontitis patients and was statistically related to clinical indices of periodontal disease including the Gingival Index, Plaque Index, and Pocket Depth. Indirect immunofluorescence microscopy is a useful technique for the rapid and reliable determination of A. actinomycetemcomitans in human subgingival dental plaque which may be applied to the clinical diagnosis, treatment, and monitoring of periodontitis associated with A. actinomycetemcomitans.

Fatty acid composition and Shwartzman activity of lipopolysaccharides from oral bacteria

The composition and the nature of the linkage of fatty acids and the Shwartzman activity of lipopolysaccharide (LPS) preparations derived from oral gram-negative bacteria including Bacteroides gingivalis, Bacteroides loesheii, Eikenella corrodens, Fusobacterium nucleatum, and Actinobacillus actinomycetemcomitans were examined. 3-Hydroxylated and nonhydroxy fatty acids of various chain lengths were found in all of the LPS preparations. All nonhydroxy fatty acids were found to be ester-bound, and part of the 3-hydroxy fatty acids in the LPS of B. gingivalis, E. corrodens, F. nucleatum, and A. actinomycetemcomitans were shown to be involved in ester linkage. It was also suggested that the hydroxy group of the ester-bound 3-hydroxy fatty acid of the LPS of F. nucleatum and A. actinomycetemcomitans is at least partly substituted by another fatty acid, but in the LPS of B. gingivalis and E. corrodens it is not. The main amide-linked fatty acid of the LPS of B. gingivalis, E. corrodens, F. nucleatum, and A. actinomycetemcomitans was 3-hydroxyheptadecanoic, 3-hydroxydodecanoic, 3-hydroxyhexadecanoic, and 3-hydroxytetradecanoic acid, respectively. The results of the Shwartzman assay showed that the E. corrodens LPS was the most active among the preparations tested, and that the Shwartzman toxicity of Bacteroides LPS is extremely low.

Subgingival microorganisms and bacterial virulence factors in periodontitis

Considerable information has come forth in recent years on the pathogenic organisms in human periodontitis and the sequence of events by which they produce periodontal disease. Important periodontopathogens include Bacteroides gingivalis, Bacteroides intermedius and Actinobacillus actinomycetemcomitans. Virulence factors of B. gingivalis and B. intermedius may mainly involve enzymes with potential to interfere with host defenses and to disintegrate periodontal tissues. Pathogenic properties of A. actinomycetemcomitans appear predominantly to be exerted by leukotoxin and other noxious products.

Actinobacillus actinomycetemcomitans in human periodontal disease

Recent evidence implicates Actinobacillus actinomycetemcomitans in the etiology of localized juvenile periodontitis. This paper reviews the morphological, biochemical and serological charcteristics of A. actinomycetemcomitans, evidence incriminating it as a periodontopathogen, its importance in human nonoral infections, and virulence factors which may be involved in the pathogenesis of A. actinomycetemcomitans infections. A. actinomycetemcomitans is a non-motile, gram-negative, capnophilic, fermentative coccobacillus which closely resembles several Haemophilus species but which does not require X or V growth factors. The organism has been categorized into 10 biotypes based on the variable fermentation of dextrin, maltose, mannitol, and xylose and into 3 serotypes on the basis of heat stable, cell surface antigens. A. actinomycetemcomitans' primary human ecologic niche is the oral cavity. It is found in dental plaque, in periodontal pockets, and buccal mucosa in up to 36% of the normal population. The organism can apparently seed from these sites to cause severe infections throughout the human body such as brain abscesses and endocarditis. There is a large body of evidence which implicates A. actinomycetemcomitans as an important micro-organism in the etiology of localized juvenile periodontitis including: (1) an increased prevalence of the organism in almost all localized juvenile periodontitis patients and their families compared to other patient groups; (2) the observation that localized juvenile periodontitis patients exhibit elevated antibody levels to A. actinomycetemcomitans in serum, saliva and gingival crevicular fluid; (3) the finding that localized juvenile periodontitis can be successfully treated by eliminating A. actinomycetemcomitans from periodontal pockets; (4) histopathologic investigations showing that A. actinomycetemcomitans invades the gingival connective tissue in localized juvenile periodontitis lesions; (5) the demonstration of several pathogenic products from A. actinomycetemcomitans including factors which may: (a) facilitate its adherence to mucosal surfaces such as capsular polysaccharides; (b) inhibit host defense mechanisms including leukotoxin, a polymorphonuclear leukocyte chemotaxis inhibiting factor, and a lymphocyte suppressing factor (c) cause tissue destruction such as lipopolysaccharide endotoxin, a bone resorption-inducing toxin, acid and alkaline phosphatases, collagenase, a fibroblast inhibiting factor and an epitheliotoxin.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation of rat B lymphocytes by Actinobacillus actinomycetemcomitans

We examined the lymphoproliferative responses of cervical lymphocytes and splenocytes of homozygous (rnu/rnu) congenitally athymic nude and normal heterozygous (rnu/+) Rowett rats to whole cells of Actinobacillus actinomycetemcomitans, a suspected periodontal disease pathogen. Previously sensitized cells from immunized only, infected only, or immunized and infected, normal rats demonstrated proliferation in response to formalinized A. actinomycetemcomitans, but cells from nude rats did not proliferate. The maximum antigenic response was observed at day 5 of culture. A. actinomycetemcomitans caused cervical lymphocytes and splenocytes from untreated naive normal and nude rats to undergo increased DNA synthesis at day 2 of culture. Highly enriched nonsensitized spleen T cells prepared on a nylon wool column did not respond to A. actinomycetemcomitans, whereas enriched nonsensitized B cells proliferated. Differences in response were probably not attributable to contributions from macrophages in the T- or B-cell populations, since macrophage percentages were approximately the same in both preparations. T-cell reconstitution of nude rats with neonatal thymus cells from rnu/+rats resulted in partial recovery of T-cell function but had no effect on the mitogenic response to A. actinomycetemcomitans. It is suggested that the antigenic responses to A. actinomycetemcomitans are dependent on T cells and that A. actinomycetemcomitans cells have mitogenic activity for B cells. The potential importance of these findings in periodontal disease is discussed.

Activation of complement system by porins extracted from Salmonella typhimurium

The effect of porins purified from Salmonella typhimurium on the complement system was investigated both in vitro and in vivo. Incubation of porins with either human or guinea pig serum resulted in the consumption of the total complement activity when an amount of porins ranging from 8 to 10 micrograms per 100 microliters of serum was used. The activation of the complement system was temperature dependent, suggesting an active process rather than passive adsorption of the complement components by porins. In addition, the activation had a fast kinetic and proceeded mainly through the classical pathway. This conclusion is supported by the consumption of C1s and C4 in normal human serum treated with porins and also by the depletion of C3 activity in the C1s-deficient serum which was marked only when purified C1s was added to the serum before incubation with porins. Injection of 100 micrograms of porins into guinea pigs induced profound complement consumption at 6 h postinjection that persisted up to 12 h. We conclude from this study that porins can effectively contribute to complement activation and to subsequent biological events induced by gram-negative bacteria.

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.

Biological activities of Eikenella corrodens outer membrane and lipopolysaccharide

Highly purified preparations of the outer membrane and lipopolysaccharide (LPS) of Eikenella corrodens strain ATCC 23834 and the outer membrane fraction (OMF) of strain 470 were tested in in vitro biological assays. The OMFs of both strains were found to be mitogenic for BDF and C3H/HeJ murine splenocytes. The E. corrodens LPS was mitogenic for BDF spleen cells; however, doses of LPS as high as 50 micrograms/ml failed to stimulate C3H/HeJ cells. When incubated with T-lymphocyte-depleted C3H/HeJ splenocytes, the strain 23834 OMF demonstrated significant mitogenic activity, indicating that the OMF is a B-cell mitogen by a mechanism other than that elicited by conventional LPS. The E. corrodens 23834 OMF and LPS were stimulators of bone resorption when tested in organ cultures of fetal rat long bones. In contrast, the strain 470 OMF was only weakly stimulatory. Both OMFs and LPSs demonstrated "endotoxic" activity, since as little as 0.062 micrograms of E. corrodens LPS and 0.015 micrograms of the OMFs induced gelation in the Limulus amebocyte clotting assay. Thus, despite having a "nonclassical" LPS biochemistry, the E. corrodens LPS elicits classical endotoxic activities. These results also indicate that the surface structures of E. corrodens have significant biological activities as measured in vitro. The expression of such activities in vivo may play an important role in the pathogenesis of periodontitis as well as other E. corrodens infections.

Isolation and characterization of the outer membrane and lipopolysaccharide from Eikenella corrodens

The chemical composition of the outer membrane fractions (OMFs) of Eikenella corrodens strains 23834 and 470 as well as the strain 23834 lipopolysaccharide (LPS) was determined. The OMFs were obtained by Triton X-100 treatment of the heavier membrane fraction from sucrose density centrifugation of the total membrane fraction. The resulting OMFs of strains 23834 and 470, free of cytoplasmic membrane components, were found to contain 69.6 and 75.0% (wt/wt) protein, 4.8 and 9.2% lipid, 4.6 and 4.7% carbohydrate, and 2.0 and 4.6% muramic acid, respectively. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis both OMFs contained one major peptide determined to be 33,500 daltons for the strain 23834 OMF, and 37,500 daltons for the strain 470 OMF. Analysis of the OMF fatty acids revealed hexadecanoic, hexadecenoic, octadecenoic, and lesser amounts of octadecanoic acids. Transmission electron microscopic examination of the OMFs revealed typical large sheets of membrane. Structures (10 nm in diameter) resembling pores were also evident. The E. corrodens LPS was found to be composed of 34.5% (wt/wt) carbohydrate and 25.0% lipid A. Only minute amounts of 2-keto-3-deoxyoctonate and heptose could be detected. Fatty acid analysis revealed primarily octadecanoic and hexadecanoic acids, with lesser amounts of octadecenoic acid. No hydroxy fatty acids were detected. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed the E. corrodens LPS to resemble other smooth-type LPSs. Transmission electron microscopic examination revealed a vesicle-like morphology. The E. corrodens LPS appears not to be a "classical," i.e., enteric, type of LPS.

Actinobacillus actinomycetemcomitans in human periodontal disease. Prevalence in patient groups and distribution of biotypes and serotypes within families

Actinobacillus actinomycetemcomitans is a Gram-negative oral bacterium which has been implicated in the etiology of localized juvenile periodontitis. In this study, 403 subjects from four study groups were examined for A actinomycetemcomitans in subgingival dental plaque. Samples pooled from at least six periodontal sites were included from each subject. A actinomycetemcomitans was detected in 28 of 29 localized juvenile periodontitis patients but in only 15% of the other subjects including 28 of 134 adult periodontitis patients, 24 of 142 periodontally healthy subjects and 5 of 98 insulin dependent juvenile diabetics with varying degrees of gingivitis. A actinomycetemcomitans isolates from members of five families with localized juvenile periodontitis patients were biotyped on the basis of variable fermentation of dextrin, maltose, mannitol and xylose and serotyped by indirect immunofluorescence using serotype specific rabbit antisera. Individuals within a family all harbored A actinomycetemcomitans of the same biotype and serotype. However, even in families with individuals heavily infected with A actinomycetemcomitans, some family members did not appear to be infected with the organism. The apparent poor transmissibility of A actinomycetemcomitans between individuals may, in part, explain the overall low prevalence of localized juvenile periodontitis and the familial pattern of the disease. The high prevalence of A actinomycetemcomitans in the subgingival plaque of localized juvenile periodontitis patients, compared to the much lower prevalence in other patient groups, supports the hypothesis that A actinomycetemcomitans is an etiologic agent in this periodontal disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Human immune responses to oral microorganisms. II. Serum antibody responses to antigens from Actinobacillus actinomycetemcomitans and the correlation with localized juvenile periodontitis

Human serum antibody responses to antigens from a suspected oral pathogen, Actinobacillus actinomycetemcomitans (Aa), were studied. IgG and IgM isotype antibodies to four antigen preparations, sonicate antigen (SA), leukotoxin (LT), group carbohydrate (LG), and lipopolysaccharide (LPS), were determined using an ELISA. An ELISA inhibition technique was developed to show that human serum antibodies reacting with the LT, LG, or LPS materials were binding to different antigenic moieties in each preparation. Cross-sectional studies of serum IgG antibodies showed that patients with localized juvenile periodontitis (LJP) had a greater frequency of occurrence and a higher level of antibodies to the SA (82%), LT (70%), and LG (62%) antigens compared to all other diseased (11-46%) or normal (4-13%) groups. Serum IgM antibodies to LPS were increased in LJP, generalized juvenile periodontitis, and adult periodontitis patients compared to all other groups. Therefore, while both IgG and IgM antibodies were found against various Aa antigens, the detection of IgG antibodies was most clearly associated with the specific disease classification of LJP. Blocking studies suggested that the human serum responses were specific for the Aa antigens and that the LT, LG, and LPS comprise major antigenic determinants on the organisms to which human serum antibody reacts.

Suppression of the periodontopathic microflora in localized juvenile periodontitis by systemic tetracycline

Since recent studies have implicated Actinobacillus actinomycetemcomitans in the etiology of localized juvenile periodontitis, this investigation determined the effectiveness of subgingival debridement, topical Betadine Solution, and systemic tetracycline in suppressing subgingival A. actinomycetemcomitans and other microorganisms. A total of 20 deep periodontal pockets and 10 normal periodontal sites of 6 localized juvenile periodontitis patients was included in the study. Each patient was treated in 3 stages over a period of 22 weeks, and the result of treatment was monitored for an additional 38 weeks. The first stage of treatment included plaque control, as well as thorough scaling and root planing, composed of at least 6 h of debridement. No concomitant periodontal surgery was performed. In the second stage, Betadine saturated cotton gauze was inserted into the periodontal pockets for 10 min. Stage 3 involved systemic tetracycline therapy (1 g/day) for 14 days. The subgingival microflora was determined at frequent intervals by selective culturing of A. actinomycetemcomitans and Capnocytophaga and by direct microscopic examination. The clinical effect was assessed by measuring changes in probing periodontal attachment level, probing periodontal pocket depth, radiographic alveolar bone mass, and other relevant clinical parameters. Scaling and root planing reduced the total subgingival bacterial counts and the proportions of certain Gram-negative bacteria, but no periodontal pocket became free of A. actinomycetemcomitans. Betadine application had little or no effect on the subgingival microflora. In contrast, tetracycline administered via the systemic route suppressed A. actinomycetemcomitans, Capnocytophaga, and spirochetes to low or undetectable levels in all test periodontal pockets. A. actinomycetemcomitans reappeared in 9 of the deep periodontal pockets after the administration of tetracycline. Most of these 9 pockets became free of detectable A. actinomycetemcomitans during the second week of tetracycline administration, whereas pockets which yielded no A. actinomycetemcomitans after tetracycline therapy became free of the organisms during the first week of tetracycline treatment. This data suggests that systemic tetracycline therapy of localized juvenile periodontitis should, as a practical rule, be continued for 3 weeks. Periodontal destruction continued in 4 deep pockets which all showed high posttetracycline A. actinomycetemcomitans counts. All 6 pockets which demonstrated a marked gain in periodontal attachment yielded no cultivable A. actinomycetemcomitans. No association was found between periodontal disease status and subgingival Capnocytophaga, spirochetes or motile rods. The present study indicates that A. actinomycetemcomitans is an important etiologic agent in localized juvenile periodontitis.(ABSTRACT TRUNCATED AT 400 WORDS)

Serology of oral Actinobacillus actinomycetemcomitans and serotype distribution in human periodontal disease

Actinobacillus actinomycetemcomitans from the human oral cavity was serologically characterized with rabbit antisera to the type strain NCTC 9710; a number of reference strains, including Y4, ATCC 29522, ATCC 29523, ATCC 29524, NCTC 9709; and our own isolates representative of each of 10 biotypes. Using immunoabsorbed antisera, we identified three distinct serotypes by immunodiffusion and indirect immunofluorescence. Serotype a was represented by ATCC 29523 and SUNYaB 75; serotype b was represented by ATCC 29522 and Y4; and serotype c was represented by NCTC 9710 and SUNYaB 67. Indirect immunofluorescence revealed no reaction between the three A. actinomycetemcomitans serotype-specific antisera and 62 strains representing 23 major oral bacterial species. Distinct from the serotype antigens were at least one A. actinomycetemcomitans species common antigen and an antigen shared with other Actinobacillus species, Haemophilus aphrophilus, and Haemophilus paraphrophilus. All serotype a A. actinomycetemcomitans strains failed to ferment xylose, whereas all serotype b organisms fermented xylose. Serotype c included xylose-positive as well as xylose-negative strains. A total of 301 isolates of A. actinomycetemcomitans from the oral cavity of 74 subjects were serologically categorized by indirect immunofluorescence with serotype-specific rabbit antisera. Each patient harbored only one serotype of A. actinomycetemcomitans. Fourteen healthy subjects, five diabetics, and seventeen adult periodontitis patients exhibited serotypes a and b in approximately equal frequency, whereas serotype c was found less frequently. In contrast, in 29 localized juvenile periodontitis patients, the incidence of serotype b was approximately two times higher than that of serotypes a or c, suggesting a particularly high periodontopathic potential of A. actinomycetemcomitans serotype b strains. In subjects infected with A. actinomycetemcomitans, serum antibodies were detected to the serotype antigens, indicating that these antigens may play a role in the pathogenesis of periodontal disease.

Ultrastructural studies of the effect of human leukocyte extracts on periodontopathic bacteria

Human gingival crevicular exudate (GE) and leukocyte extracts (LE) were previously shown to be able to release the bulk of radioactivity from a variety of 14C-labeled oral bacteria. The present study demonstrates that the release of radiolabel by these enzymatic agents from two periodontopathic bacteria (Actinobacillus actinomycetemcomitans strain Y4 and Capnocytophaga sputigena strain 4) is accompanied by both cell wall and cytoplasmatic damage. The possible role of bacterial products released by lysosomal enzymes, present in the gingival crevice, is discussed.

A rationale for management of periodontal diseases: rapid identification of microbial 'therapeutic targets' with phase-contrast microscopy

Monitoring the composition of subgingival flora can provide clinicians with a supplement to periodontal diagnosis and therapy. Conventional bacteriologic culturing may be clinically impractical, but direct microscopy may not.

Effect of human leukocyte extracts and gingival exudate on periodontopathic bacteria

The effect of leukocyte hydrolytic enzymes on periodontopathic bacteria was examined in vitro. A frozen and thawed extract of human peripheral blood leukocytes (LE) and human gingival crevicular exudate (GE) were shown to be able to cause the release of 50% of the radioactivity from a leukotoxic strain of Actinobacillus actinomycetemcomitans (Aa Y4), labeled by 14C. A nonleukotoxic strain (Aa 653) was shown to be more susceptible to both LE and GE, up to 68% of the total radioactivity was solubilized by LE at pH 7.4. Both bacterial strains were found to be resistant to the activity of lysozyme, but highly susceptible to lysolecithin and mixtures of lysolecithin and lysozyme or LE. Capnocytophaga sputigena strain 4 was also found to be partially susceptible to the effect of LE and GE. The possible role of leukocyte hydrolytic enzymes in bacteriolysis and release of bacterial products in relation to periodontal disease is discussed.

Cytotoxicity of the bacterium Actinobacillus actinomycetemcomitans extracts in human gingival fibroblasts

Filter-sterilized sonic extracts (SE) of strains of Actinobacillus actinomycetemcomitans were shown to inhibit the proliferation of human gingival fibroblasts in vitro. The inhibition was dose-dependent: a 50 per cent inhibitory dose of 2 micrograms protein/ml was found for A. actinomycetemcomitans strain Y4. The inhibitory activity could be neutralized by homologous antiserum and was heat inactivated by temperatures of 80 degrees C or greater. The fibroblast-inhibitory activity was present in SEs of both leukotoxic-producing and non-leukotoxic strains of A. actinomycetemcomitans, suggesting that a separate agent is responsible for leukotoxicity and fibroblast inhibition. A short (10 min) exposure of the fibroblasts to the A. actinomycetemcomitans SE was sufficient to inhibit irreversibly cell proliferation, provided that serum was present at the time that the cells were exposed to the SE. SE-challenged fibroblasts exhibited a marked decrease in the rate of DNA synthesis, but no inhibition of RNA or protein synthesis. Although the SE-treated cells did not proliferate, they appeared to remain intact and viable; and displayed no gross morphological alterations.

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

The major cell envelope protein compositions of seven Actinobacillus actinomycetemcomitans strains of human origin were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The major envelope polypeptides were homogeneous, in relation to molecular weight, in all of the strains that were examined. The characterization of the five major proteins, designated Env1 through Env5, in the leukotoxic strain Y4 revealed that proteins Env2 to -5 may reside in the outer membrane as suggested by differential detergent extractions and 125I-labeling experiments. The proteins did not demonstrate covalent or ionic interactions with the peptidoglycan; however, one protein, Env2, displayed heat-modifiable properties, having apparent molecular weights of 32,000 and 45,000 when heated in sodium dodecyl sulfate at 50 and 100 degrees C, respectively. The protein composition of the extracellular "bleb" material, normally released by strain Y4, was determined, and proteins Env1 to -4 were the predominant protein species found. A comparison of the cell envelope proteins of strain Y4 with those of other members of the human oral flora, including species within the genera Capnocytophaga, Bacteroides, and Fusobacterium, revealed distinct differences on the basis of molecular size and heat-modifiable properties. However, the membrane proteins of Haemophilus aphrophilus showed a remarkable degree of homology with those of A. actinomycetemcomitans.

Inhibition of fibroblast proliferation by Actinobacillus actinomycetemcomitans

We have examined soluble sonic extracts of Actinobacillus actinomycetemcomitans for their ability to alter human and murine fibroblast proliferation. We found that extracts of all A. actinomycetemcomitans strains examined (both leukotoxic and nonleukotoxic) caused a dose-dependent inhibition of both murine and human fibroblast proliferation as assessed by DNA synthesis ([3H]thymidine incorporation). Addition of sonic extract simultaneously with [3H]thymidine had no effect on incorporation, indicating that suppression was not due to the presence of excessive amounts of cold thymidine. Inhibition of DNA synthesis was also paralleled by decreased RNA synthesis ([3H]uridine incorporation) and by a decrease in cell growth as assessed by direct cell counts; there was no effect on cell viability. The suppressive factor(s) is heat labile; preliminary purification and characterization studies indicate that it is a distinct and separate moiety from other A. actinomycetemcomitans mediators previously reported, including leukotoxin, immune suppressive factor, and endotoxin. Although it is not clear how A. actinomycetemcomitans acts to cause disease, we propose that one aspect of the pathogenicity of this organism rests in its ability to inhibit fibroblast growth, which in turn could contribute to the collagen loss associated with certain forms of periodontal disease, in particular juvenile periodontitis.

Selective medium for isolation of Actinobacillus actinomycetemcomitans

A selective medium, TSBV (tryptic soy-serum-bacitracin-vancomycin) agar, was developed for the isolation of Actinobacillus actinomycetemcomitans, TSBV agar contained (per liter) 40 g of tryptic soy agar, 1 g of yeast extract, 100 ml of horse serum. 75 mg of bacitracin, and 5 mg of vancomycin. The TSBV medium suppressed most oral species and permitted significantly higher recovery of A. actinomycetemcomitans than nonselective blood agar medium. The distinct colonial morphology and positive catalase reaction of A. actinomycetemcomitans easily distinguished this bacterium from Haemophilus aphrophilus, Capnocytophaga species, and a few other contaminating organisms. With the TSBV medium, even modestly equipped laboratories will be able to isolate and identify A. actinomycetemcomitans from clinical specimens.

Characterization of an inducible bacteriophage from a leukotoxic strain of Actinobacillus actinomycetemcomitans

A bacteriophage, designated phi Aa17, was isolated by mitomycin C induction from leukotoxic Actinobacillus actinomycetemcomitans strains 651. Electron microscopy of the virus revealed particles with regular, nonelongated, polyhedral heads, and tails consisting of a contractile sheath and core. Spikes emanated from the base of the tail. The head had a diameter of 70 nm. The fully extended tail sheath had a length of 127 nm and a diameter of 22 nm. In its contracted form, the tail sheath measured 47 nm in length and 25 nm in diameter. The phage had a buoyant density of 1.370 in CsCl, and its genome was found to be double-stranded DNA. A single-cycle growth curve revealed that the phage had a latent period of 30 min and a burst size of 435 PFU per cell. The host range of the phage was examined, and A. actinomycetemcomitans strains ATCC 29523 and ATCC 29524 were found to be phage sensitive, whereas strains Y4, ATCC 29522, 2043, 652, 651, 627, 2097, N27, 2112, and 511 were resistant. The host range of this virus does not suggest any association between the phage and leukotoxin production.

Cellular fatty acid and soluble protein composition of Actinobacillus actinomycetemcomitans and related organisms

The cellular fatty acid and protein content of twenty-five representative strains of Actinobacillus actinomycetecomitans isolated from juvenile and adult periodontitis patients was compared to that of 15 reference strains of oral and nonoral Actinobacillus species and Haemophilus aphrophilus. Trimethylsilyl derivatives of the fatty acid methyl esters were analyzed by gas-liquid chromatography. The predominant fatty acids of all 40 strains examined were 14:0, 3-OH 14:0, 16 delta, and 16:0. Actinobacillus seminis (ATCC 15768) was unlike the other strains examined because of a greater amount of 14:0 detected. The soluble protein analysis using polyacrylamide gel electrophoresis revealed that A. actinomycetemcomitans, H. aphrophilus, and nonoral Actinobacillus species possessed distinct protein profiles attesting to the validity of separating these organisms into different species. Established biotypes of A. actinomycetemcomitans could not be differentiated on the basis of fatty acid or protein profiles.