[THE CHARACTERISTICS OF MORPHOLOGY OF BIOFILM OF PERIODONTIUM UNDER INFLAMMATORY DISEASES OF GUMS (CHRONIC CATARRHAL GINGIVITIS, CHRONIC PERIODONTITIS, CANDIDA-ASSOCIATED PERIODONTITIS) ACCORDING RESULTS OF ELECTRONIC MICROSCOPY]

The study was carried out to analyze morphology of biofilm of periodontium and to develop electronic microscopic criteria of differentiated diagnostic of inflammatory diseases of gums. The scanning electronic microscopy was applied to analyze samples of bioflm of periodont from 70 patients. Including ten patients with every nosologic form of groups with chronic catarrhal periodontitis. of light, mean and severe degree, chronic catarrhal gingivitis, Candida-associated paroperiodontitis and 20 healthy persons with intact periodontium. The analysis was implemented using dual-beam scanning electronic microscope Quanta 200 3D (FEI company, USA) and walk-through electronic micJEM 100B (JEOL, Japan). To detect marker DNA of periodont pathogenic bacteria in analyzed samples the kit of reagentsfor polymerase chain reaction "MultiDent-5" ("GenLab", Russia). The scanning electronic microscopy in combination with transmission electronic microscopy and polymerase chain reaction permits analyzing structure, composition and degree of development of biofilm of periodontium and to apply differentiated diagnostic of different nosologic forms of inflammatory diseases of periodontium, including light form of chronic periodontitis and gingivitis. The electronic microscopical indications of diseases ofperiodontium of inflammatory character are established: catarrhal gingivitis, (coccal morphological alternate), chronic periodontitis (bacillary morphological alternate), Candida-associated periodontitis (Candida morphological alternate of biofilm ofperiodontium).

[Invasion of four common periodontal pathogens into vascular endothelial cells in vitro]

OBJECTIVE

To investigate the adhesive and invasive ability of four common periodontal pathogens, Pg33277, Pi25611, Aa29522 and Fn10953 in human umbilical vein endothelial cells (HUVEC).

METHODS

The model of infection of HUVEC by periodontal pathogens was established in vitro. The invasive ability of four periodontal pathogens in HUVEC was tested by scanning electron microscope (SEM) and antibiotic protection assays-colony-forming units (CFU).

RESULTS

All of the four periodontal pathogens were found to adhere to HUVEC by SEM and invaded HUVEC at invasion numbers of (0.8 +/- 0.1) x 10(8), (4.1 +/- 0.5) x 10(6), (1.6 +/- 0.3) x 10(6) and (5.0 +/- 0.4) x 10(6) CFU/L respectively by antibiotic protection assays-CFU. The invasion efficiencies were (0.400 +/- 0.050)%, (0.021 +/- 0.003)%, (0.008 +/- 0.002)% and (0.025 +/- 0.002)%, respectively. The invasive ability of Pg33277 was significantly greater than those of the other three periodontal pathogens (P < 0.001). There was no difference in invasive abilities among Pi25611, Aa29522 and Fn10953 (P > 0.05).

CONCLUSIONS

All of the four common periodontal pathogens, Pg33277, Pi25611, Aa29522 and Fn10953 could adhere to and invaded HUVEC, with Pg33277 being the strongest.

Actinobacillus actinomycetemcomitans adheres to human gingival fibroblasts and modifies cytoskeletal organization

Adherence of Actinobacillus actinomycetemcomitans to human gingival fibroblast cells induces cytoskeletal reorganization. A. actinomycetemcomitans is considered a pathogenic bacteria involved in localized aggressive periodontitis. Studies with epithelial cells have shown an adherent capacity of bacteria that is increased under anaerobic conditions. For adherence to take place, there is a need for interaction between extracellular vesicles and bacterial fimbriae. However, molecular events associated with the adherence process are still unknown. The aim of this study was to investigate whether A. actinomycetemcomitans adherence to human gingival fibroblasts promotes cytoskeletal reorganization. Adherence was determined with light microscopy and scanning electron microscopy. For F-actin visualization, cells were treated with fluorescein-isothiocyanate-phalloidin and samples were examined with epifluorescence optics. Fluorescent was recorded on Kodak T-Max 400 film. We showed that A. actinomycetemcomitans adheres to human gingival fibroblast primary cultures, this property stimulating an increase in the intracellular calcium levels. In human gingival fibroblast primary cultures, we observed that maximal A. actinomycetemcomitans adherence took place 1.5h after culture infection occurred and remained for 6h. The adherence was associated with morphologic alterations and an increased in the intracellular calcium levels. These experiments suggest that A. actinomycetemcomitans adherence cause morphological alterations, induce actin stress fibers and recruitment of intracellular calcium levels.

Novel surface structures are associated with the adhesion of Actinobacillus actinomycetemcomitans to collagen

Actinobacillus actinomycetemcomitans is a gram-negative, facultative, anaerobic bacterium that colonizes the human oral cavity and the upper respiratory tract. This bacterium is strongly associated with localized aggressive periodontitis and adult periodontitis and is the causative agent for other serious systemic infections. Recently, we have identified a protein, EmaA (extracellular matrix protein adhesin A), that mediates the adhesion of A. actinomycetemcomitans to collagen. The conserved sequence and predicted secondary structure suggest that EmaA is an orthologue of the Yersinia enterocolitica adhesin YadA. Electron microscopy examinations of A. actinomycetemcomitans have identified antenna-like protrusions associated with the surface of the bacterium. These structures are absent on emaA mutant strains and can be restored by transformation of the mutant strain with emaA in trans. The loss of these structures is associated with a decrease in the binding of this bacterium to collagen. The antenna-like structures are composed of a long rod that terminates in an ellipsoidal head region. The analysis of these structures using image processing techniques has provided an initial estimate of the overall dimensions, which suggests that the appendages are oligomeric structures formed by either three or four subunits. Together, the data suggest that emaA is required for the expression of novel appendages on the surface of A. actinomycetemcomitans that mediate the adhesion of the bacterium to collagen.

Susceptibility of Actinobacillus actinomycetemcomitans to six antibiotics decreases as biofilm matures

OBJECTIVES

Actinobacillus actinomycetemcomitans is a major causative agent of chronic and aggressive periodontitis. Freshly isolated strains of A. actinomycetemcomitans display rough-type colonies and initiate biofilm formation on glass surfaces. The purpose of this study was to determine the antibiotic susceptibility of A. actinomycetemcomitans biofilm during different phases of maturation.

METHODS

Using 96-well microtitre plates, we determined the antibiotic susceptibility of rough-type strain 310a to concentrations from 0.1 to 10 mg/L each of erythromycin, ofloxacin, ampicillin, cefalexin, tetracycline and minocycline during biofilm formation. Antibiotics were added at the start of the culture (early phase) and after 24 h of cultivation (mature phase).

RESULTS

Adding 10 mg/L of ampicillin, 10 mg/L of cefalexin, 0.1 or 1 mg/L of tetracycline, or 0.1 mg/L of minocycline significantly inhibited 310a biofilm formation in the early phase, but not in the mature phase. Although adding 10 mg/L of erythromycin, tetracycline or minocycline reduced biofilm development in the early phase, it enhanced 310a biofilm development in the mature phase. Ofloxacin exerted a strong inhibitory effect in both the early and mature phases of biofilm formation throughout all experiments.

CONCLUSIONS

The present study demonstrated that the susceptibility of A. actinomycetemcomitans to many antibiotics decreased after biofilm maturation.

A simple viability-maintaining method produces homogenic cell suspensions of autoaggregating wild-type Actinobacillus actinomycetemcomitans

Tenacious adherence and autoaggregation of wild-type Actinobacillus actinomycetemcomitans strains jeopardize reliability of determined cell concentrations, e.g. for studies on bacteria-host interactions. We first compared the efficacy of two methods, an indirect and a direct method, for homogenizing cell suspensions of a wild-type, autoaggregating (SA269) strain and of a non-autoaggregating laboratory variant (ATCC 43718) used as a reference. Since the direct method left visible clumps in SA269 suspension, only the indirect method was further tested. In serial dilutions of the homogenized cell suspensions of strains SA269 and ATCC 43718, the OD600 values (R2=0.99, R2=0.99, respectively) and protein concentrations (R2=0.93, R2=0.95, respectively) correlated significantly (all P<0.002) with the dilution factor. There were no differences (P>0.05) in the bacterial viable counts between the two strains or between suspending solutions, i.e., PBS and water, the cell concentrations demonstrating 1x10(9) cells/ml at OD600=1. Repeated microscopic cell counts did not differ (P>0.05) from each other. Large aggregates occurred as 1% of cell units counted. Dispersing bacterial mass indirectly to solution leads to homogeneous cell suspensions with repeatable cell concentrations. Viability of A. actinomycetemcomitans was also maintained when cells were suspended in water.

Environmental influences on Actinobacillus actinomycetemcomitans biofilm formation

Fresh clinical isolates of the periodontal pathogen Actinobacillus actinomycetemcomitans have an adherent, rough colony morphology that transforms into a minimally adherent, smooth colony phenotype during successive in vitro passage. The objectives of this study were: (1) to compare biofilm formation of the rough (RVs) and smooth variants (SVs) of several strains of A. actinomycetemcomitans grown under various environmental conditions and (2) to examine the dynamics of biofilm formation. A microtitre plate biofilm assay was used to evaluate biofilm formation of strains grown in broth with modified salt concentration and pH, and to evaluate the effect of pre-conditioning films. Scanning electron microscopy (SEM) was used to monitor microscopic changes in morphology. Dynamics of biofilm formation were measured in a flowcell monitored by confocal microscopy. The RVs generally produced greater biofilm than the SVs. However, medium-dependent differences in biofilm formation were evident for some rough/smooth pairs. The RVs were more tolerant to changes in salt and pH, and more resistant to chlorhexidine than the SVs. Horse serum virtually eliminated, and saliva significantly reduced, biofilm formation by the SVs in contrast to the RVs. SEM revealed no alteration in morphology with change of environment. In a flowcell, the RVs produced towers of microcolonies anchored by a small contact area, whereas the SVs produced an open architecture of reduced height. After 7 days in a flowcell, the rough to smooth phenotype transition could be demonstrated. In conclusion, strain, growth medium and conditioning film all affect biofilm formation. The RVs produce biofilms of unique architecture that may serve to protect the bacterium from environmental perturbations.

Apoptotic activity and sub-cellular localization of a T4SS-associated CagE-homologue in Actinobacillus actinomycetemcomitans

A potent virulence factor, cagE homologue of Actinobacillus actinomycetemcomitans, was identified via an expression cloning strategy and periodontitis-associated CD4(+)T-cells of a humanized mouse model. Through the immuno-gold labeling with transmission electron microscopy, immunofluorescent staining, in vitro co-cultures and Western blot studies, the resulting data clearly demonstrate that: (i) in CagE-homologue treated human epithelia in vitro, there are ultra-structural features of plasma membrane blebbing, sub-cellular disorganization with condensed and marginalized chromatins along the nuclear membrane, consistent with the pro-apoptotic characteristics, (ii) the disturbed membrane integrity detected above is associated with localization of the CagE proteins on target cell surface, and (iii) CagE-homologue is located in the cytoplasm of A. actinomycetemcomitans and associated with a bacterial type-IV secretion system (T4SS), suggesting that its translocation is required for secretion. Thus, CagE-homologue may be critically involved in A. actinomycetemcomitans-induced tissue destruction, inflammation and subsequent adverse immunity in periodontal pathogenesis.

Genetic basis for conversion of rough-to-smooth colony morphology in Actinobacillus actinomycetemcomitans

The basis of the rough-to-smooth conversion of Actinobacillus actinomycetemcomitans was examined. Smooth variants often contained mutations at the flp promoter region. Replacing the mutated flp promoter with the wild-type promoter restored the rough phenotype. The expression level of the flp promoter was approximately 100-fold lower in smooth than in rough strains. Mutations of the flp promoter are a cause of the rough-to-smooth conversion.

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.

Detection of subgingival calculus and dentine caries by laser fluorescence

OBJECTIVES

Detection of subgingival calculus and dentine caries in the bottom of deep periodontal pockets is often difficult without visual observation. We thus examined the possibility of its detection using autofluorescence induced by laser irritation.

METHODS

Autofluorescence was measured at various excitation and emission wavelength settings in five specimens each of sound dentine and enamel, subgingival calculus, and root caries. Periodontopathic model teeth with bacterial cells and blood clots were also irritated by laser to obtain autofluorescent images.

RESULTS

Subgingival calculus and dentine caries showed a characteristic 700 nm emission when excited at 635 nm or a 720 nm emission when excited at 655 nm; sound dentine or enamel, however, did not. The calculus differentiation power, however, was higher with excitation at 635 nm than at 655 nm. The autofluorescent images photographed at an excitation of 633 nm provided clear calculus identification in periodontopathic model teeth when a 700 nm band-pass filter or a 700 nm high-pass filter was used. However, fluorescence intensity was masked when the calculus surface was covered by bacterial cells or blood clots. For clinical use, it would be important to remove subgingival plaque and debris from root surfaces before attempting to detect subgingival calculus and root caries with this manner.

CONCLUSION

The autofluorescence method employing excitation of 633-635 nm was found to be a powerful tool for detecting subgingival calculus and root caries.

Outer membrane protein 100, a versatile virulence factor of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans (Aa) is one of the pathogenic bacteria involved in periodontal diseases. We have previously identified six major outer membrane proteins (Omps) of Aa Y4. Among them is an Omp with high molecular mass, designated Omp100, which has homology to a variety of virulence factors. Electron microscopic observation indicated that Omp100 is randomly localized on the cell surface of Aa. Aa Y4 has been shown to adhere and invade KB or normal human gingival keratinocytes. Anti-Omp100 antibody inhibited 50% of adhesion and 70% of invasion of Aa Y4 to KB cells. An Omp100 knock-out mutant had a decreased adhesion and invasion efficiency of 60%, compared with that of the wild type. Escherichia coli HB101 expressing Omp100 adhered twofold and invaded 10-fold more than the wild-type E. coli HB101. HB101 expressing Omp100 showed resistance to serum by trapping factor H, an inhibitor for C3b, with Omp100. Omp100 induced inflammatory cytokine responses of interleukin (IL)-8, IL-6 and tumour necrosis factor (TNF)alpha in epithelial cells, and induced IL-1beta and TNFalpha production in mouse macrophages. These results indicate that Omp100 is a versatile virulence factor that may demonstrate potential significance in the onset of periodontal diseases related to Aa.

Biofilm growth and detachment of Actinobacillus actinomycetemcomitans

The gram-negative, oral bacterium Actinobacillus actinomycetemcomitans has been implicated as the causative agent of several forms of periodontal disease in humans. When cultured in broth, fresh clinical isolates of A. actinomycetemcomitans form tenacious biofilms on surfaces such as glass, plastic, and saliva-coated hydroxyapatite, a property that probably plays an important role in the ability of this bacterium to colonize the oral cavity and cause disease. We examined the morphology of A. actinomycetemcomitans biofilm colonies grown on glass slides and in polystyrene petri dishes by using light microscopy and scanning and transmission electron microscopy. We found that A. actinomycetemcomitans developed asymmetric, lobed biofilm colonies that displayed complex architectural features, including a layer of densely packed cells on the outside of the colony and nonaggregated cells and large, transparent cavities on the inside of the colony. Mature biofilm colonies released single cells or small clusters of cells into the medium. These released cells adhered to the surface of the culture vessel and formed new colonies, enabling the biofilm to spread. We isolated three transposon insertion mutants which produced biofilm colonies that lacked internal, nonaggregated cells and were unable to release cells into the medium. All three transposon insertions mapped to genes required for the synthesis of the O polysaccharide (O-PS) component of lipopolysaccharide. Plasmids carrying the complementary wild-type genes restored the ability of mutant strains to synthesize O-PS and release cells into the medium. Our findings suggest that A. actinomycetemcomitans biofilm growth and detachment are discrete processes and that biofilm cell detachment evidently involves the formation of nonaggregated cells inside the biofilm colony that are destined for release from the colony.

Outer membrane-like vesicles secreted by Actinobacillus actinomycetemcomitans are enriched in leukotoxin

Actinobacillus actinomycetemcomitans is associated with early onset periodontal diseases and secretes membranous vesicles that appear to contain several virulence-associated proteins. However, the composition of these vesicles and the process leading to their secretion are not well defined. Electron micrographs of thin sectioned bacterial cells and purified vesicle preparations showed that vesicles are spherical lipid bilayers, 50-100 nm in diameter, that appear to form by budding from the outer membrane of the bacterium. Thin layer chromatography identified the predominant lipid components of vesicles as lipopolysaccharide, phosphatidylethanolamine and cardiolipin, similar to the main lipid constituents of the outer membrane. However, vesicles also contained minor lipids that were not detected in outer membrane samples. The major protein constituents of vesicles co-migrated with proteins in outer membrane extracts of A. actinomycetemcomitans, but the outer membrane preparations possessed polypeptides that were not detected in vesicles. Three vesicle proteins were identified; the heat-modifiable OmpA homologue of A. actinomycetemcomitans, a 28 kDa lipoprotein related to the major outer membrane lipoprotein of Mannheimia haemolytica and leukotoxin. Incubation of leukotoxin-sensitive human HL60 cells with vesicles from A. actinomycetemcomitans strains JP2 and 652 resulted in cell lysis, indicating that vesicle-associated leukotoxin is biologically active. Vesicles from the highly leukotoxic strain JP2 were five- to 10-fold more toxic than vesicles from the minimally leukotoxic 652 strain. Furthermore, the specific leukotoxic activity of JP2 vesicles was approximately four- to five-fold higher than isolated outer membrane preparations from JP2, suggesting that vesicles are enriched in leukotoxin. Together, these results suggest that the formation of A. actinomycetemcomitans vesicles occurs by a process that results in the enrichment of leukotoxin.

Adherence of Actinobacillus actinomycetemcomitans on oral epithelial cells

Actinobacillus actinomycetemcomitans is capable of colonizing mucosa and dental plaque and plays an important role in periodontal disease in young peoples and adult. Adherence mechanisms on epithelial cells, tooth or oral bacteria and gingival invasion probably are the initial steps in the pathogenesis of gingivitis or periodontitis. In this study, the adherence of A. actinomycetemcomitans on oral epithelial cells following subculturing were examined. The adherence on oral epithelial cells showed high in all the isolates values but with differences among them and at each time of subculturing. The adherence of A. actinomycetemcomitans FDC Y4 was stable in each of the subcultures. However, adhesion values of all the tested isolates were different except for strains #1, #38 and Y4, suggesting a heterogenicity within this microbial group. Morphologic variations were observed in extracellular structures of the A. actinomycetemcomitans tested. The adhesion process on oral epithelial cells of this organism can be influenced by subcultures, but additional studies are necessary to verify the influence of subculturing on adherence or other virulence factors.

Nonspecific adherence and fibril biogenesis by Actinobacillus actinomycetemcomitans: TadA protein is an ATPase

Cells of Actinobacillus actinomycetemcomitans, a gram-negative pathogen responsible for an aggressive form of juvenile periodontitis, form tenaciously adherent biofilms on solid surfaces. The bacteria produce long fibrils of bundled pili, which are required for adherence. Mutations in flp-1, which encodes the major subunit of the pili, or any of seven downstream tad genes (tadABCDEFG) cause defects in fibril production, autoaggregation, and tenacious adherence. We proposed that the tad genes specify part of a novel secretion system for the assembly and transport of Flp pili. The predicted amino acid sequence of TadA (426 amino acids, 47,140 Da) contains motifs for nucleotide binding and hydrolysis common among secretion NTP hydrolase (NTPase) proteins. In addition, the tadA gene is the first representative of a distinct subfamily of potential type IV secretion NTPase genes. Here we report studies on the function of TadA. The tadA gene was altered to express a modified version of TadA that has the 11-residue epitope (T7-TAG) fused to its C terminus. The TadA-T7 protein was indistinguishable from the wild type in its ability to complement the fibril and adherence defects of A. actinomycetemcomitans tadA mutants. Although TadA is not predicted to have a transmembrane domain, the protein was localized to the inner membrane and cytoplasmic fractions of A. actinomycetemcomitans cells, indicating a possible peripheral association with the inner membrane. TadA-T7 was purified and found to hydrolyze ATP in vitro. The ATPase activity is stimulated by Triton X-100, with maximal stimulation at the critical micellar concentration. TadA-T7 forms multimers that are stable during sodium dodecyl sulfate-polyacrylamide gel electrophoresis in nonreducing conditions, and electron microscopy revealed that TadA-T7 can form structures closely resembling the hexameric rings of other type IV secretion NTPases. Site-directed mutagenesis was used to substitute Ala and Gln residues for the conserved Lys residue of the Walker A box for nucleotide binding. Both mutants were found to be defective in their ability to complement tadA mutants. We suggest that the ATPase activity of TadA is required to energize the assembly or secretion of Flp pili for tight adherence of A. actinomycetemcomitans.

Molecular strategies for fimbrial expression and assembly

Fimbriae or pili are long, filamentous, multimeric macromolecules found on the bacterial cell surface. Bacteria express a diverse array of fimbriae or pili that are involved in bacterial adherence and invasion. Fimbriae can be categorized based on their modes of expression and assembly. Type I fimbriae and P pili are distributed peritrichously and translocated to the cell surface by a chaperone/usher pathway. Type 4 pili are located at the pole of the cell and assembled via the type II secretion system. Curli fimbriae are coiled surface structures assembled by an extracellular nucleation/precipitation pathway. Fimbriae of oral gram-negative and gram-positive bacteria have not been well-studied as compared with the fimbriae of enteric pathogens. Oral pathogens, such as Eikenella corrodens, Actinobacillus actinomycetemcomitans, and Porphyromonas gingivalis, possess fimbriae that have been implicated in bacterial adhesion and invasion. These fimbriae are potential virulence factors in oral infectious processes. A. actinomycetemcomitans and E. corrodens have Type 4-like fimbriae, whereas P. gingivalis displays a unique type of fimbriae. To date, fimbriae of the oral primary colonizers, Actinomyces naeslundii and Streptococcus parasanguis, represent the only fimbriae characterized for any gram-positive bacteria. The putative major fimbrial subunits, FimA and FimP of A. naeslundii and Fap1 of S. parasanguis, contain a signal sequence and cell-wall-sorting signal. The presence of extensive dipeptide repeats in Fap1 makes it unique among fimbrial molecules. Based on experimental data, a nucleation/precipitation pathway is proposed for fimbrial biogenesis of both S. parasanguis and A. naeslundii, although we cannot rule out an alternative covalent linkage model. The model systems described in this review served as a framework for hypotheses for how the known molecular factors of fimbriae on oral bacteria may be expressed and assembled.

Tenacious adhesion of Actinobacillus actinomycetemcomitans strain CU1000 to salivary-coated hydroxyapatite

Adherence of Actinobacillus actinomycetemcomitans to hard-tissue surfaces was evaluated by comparing a phenotypically stable, well-maintained clinical isolate (strain CU1000) to Streptococcus gordonii G9B, an extensively studied oral-colonizing bacterium. Standard innocula of radiolabelled bacteria were added to saliva-coated hydroxyapatite (SHA) and the ratio of bound to unbound cells counted. Several other clinical isolates as well as laboratory strain Y4 were studied. In other experiments, cell detachment from SHA was compared in static and shaking vessels to calculate controlled desorption of cells over time. A sonic-displacement assay was used to measure avidity of binding to HA and SHA. To better define the attachment properties of CU1000, bacteria were treated with a variety of agents including detergents, salts and enzymes before or after incubation with SHA. Results indicated that CU1000 bound better than G9B (a minimum of 10-fold greater; p < or = 0.05) and did not desorb from SHA, while G9B desorbed to equilibrium in 4 h. Furthermore, Langmuir isotherm calculations indicated that, unlike G9B, CU1000 did not follow second-order adsorption kinetics and thus did not achieve saturation. In addition, of the agents tested only periodate reduced attachment and resulted in detachment of CU1000 from surfaces. These experiments suggest that clinical isolates of A. actinomycetemcomitans possess unique binding properties that promote adsorption to and impede desorption from SHA. The characteristics described for the actinobacillus in this study have been previously underestimated, appear to be mediated by glycoconjugates, and may resemble attachment described for several biofilm-forming, non-oral pathogens.

Phenotypic variation in Actinobacillus actinomycetemcomitans during laboratory growth: implications for virulence

This study examined alteration of specific virulence traits associated with phenotypic changes seen when a low-passage disease-associated and well maintained parent strain of Actinobacillus actinomycetemcomitans was compared to a laboratory-grown spontaneous variant/mutant. Clinical isolates of A. actinomycetemcomitans recovered from periodontitis patients typically grow as rough, adherent colonies on primary culture but undergo transformation to smooth, non-adherent colonies following repeated passage in vitro. The relationship of these phenotypic changes to the virulence of the organism or to the processes that underlie this transformation are not understood. A fresh clinical isolate, designated strain CU1000, was obtained from the first molar site of a patient with classical signs of localized juvenile periodontitis and used as the parent strain to study virulence-related phenotypes. Following several passages of CU1000 on selective agar, a spontaneous variant that demonstrated smooth, opaque, non-adherent colonies was isolated and designated strain CU1060. This study compared the properties of these two strains with respect to colony morphology, autoaggregation, surface appendages, adherence to saliva-coated hydroxyapatite (SHA), LPS chemotype and activity, induction of fibroblast proteinase activity and antigenic properties. CU1000 demonstrated rough, raised, star-positive colonies which upon electron microscopic examination revealed the presence of large, flexible, bundled fibrils. In addition, CU1000 showed adherence to SHA, several unique protein antigens and elevated endotoxin and fibroblast proteinase activity. CU1060, on the other hand, showed minimal adherence to SHA and fewer reactive proteins compared to the fresh clinical isolates. This strain formed smooth, opaque colonies on agar, showed minimal fibril formation and limited endotoxin and fibroblast-proteinase-inducing activity. These findings demonstrate that clinical isolates of A. actinomycetemcomitans undergo significant virulence-reducing phenotypic alterations during in vitro passage and support the need to study this organism in its clinical form.

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.

Molecular characterization of low-molecular-weight component protein, Flp, in Actinobacillus actinomycetemcomitans fimbriae

Fimbriae preparation from Actinobacillus actinomycetemcomitans was found to contain an abundant low-molecular-weight protein (termed Flp) with an apparent molecular mass of approximately 6.5 kDa, in addition to a small amount of 54-kDa protein. Immunogold electron microscopy localized the Flp protein at the bacterial fimbriae but not at the cell surface. The DNA fragment including the flp gene was cloned from A. actinomycetemcomitans 304-a and its nucleotide sequence was determined. An open reading frame of the flp gene was composed of 225 bp encoding a protein of 75 amino acids. Comparison of the translated amino acid sequence with the sequence of native Flp determined by Edman degradation indicated that the N-terminal part of 26 amino acids is leader peptide. The N-terminal sequence of mature Flp exhibited some similarity to type-IV pilin. Furthermore, the processing site of premature Flp is also similar to that of type-IV prepilin, and a gene encoding a protein homologous to type-IV prepilin-like protein leader peptidase was found downstream of the flp gene. These findings indicate that Flp is the major component protein of A. actinomycetemcomitans fimbriae.

Invasion of epithelial cells by Actinobacillus actinomycetemcomitans: a dynamic, multistep process

The invasion process of Actinobacillus actinomycetemcomitans, a periodontopathogen, was studied with microscopy and viable quantitative assays using both KB and Madin-Darby canine kidney (MDCK) epithelial cells. Microscopy revealed that the events associated with the A. actinomycetemcomitans invasion process occurred rapidly. Scanning electron micrographs revealed A. actinomycetemcomitans associated with craters on the KB cell surface and others entering the KB cells through apertures with lip-like rims within 30 min of infection. Both transmission electron and immunofluorescence micrographs demonstrated that by this time some bacteria had, in fact, already entered, replicated, and exited host cells. Scanning electron micrographs revealed that infected KB cells exhibited fibrillar protrusions which contained bulges with the conformation of bacteria. Some protrusions formed intercellular connections between KB cells. Immunofluorescence micrographs revealed protrusions which harbored A. actinomycetemcomitans. The spread of internalized A. actinomycetemcomitans from one MDCK epithelial cell monolayer to another was demonstrated using a sandwich assay developed in our laboratory. Transcytosis of A. actinomycetemcomitans through polarized MDCK cells was also demonstrated. This study indicates that soon after entry of A. actinomycetemcomitans bacteria into epithelial cells, they undergo rapid multiplication and may subsequently be found in protrusions which sometimes extend between neighboring epithelial cells. The protrusions are thought to mediate the cell-to-cell spread of A. actinomycetemcomitans. Cell-to-cell spread may also occur by the endocytosis of A. actinomycetemcomitans bacteria which have been released into the medium via rudimentary protrusions which do not interconnect epithelial cells. The finding that the A. actinomycetemcomitans invasion process is so dynamic sheds significant new light on the interaction of this periodontopathogen with mammalian cells.

Delmopinol interactions with cell walls of gram-negative and gram-positive oral bacteria

The main purpose of the present study was to investigate the influence of delmopinol hydrochloride on the cell surface morphology of gram-negative and gram-positive bacterial cells by using transmission electron microscopy. A second purpose was to evaluate the extraction of cell wall material caused by delmopinol and the binding of radiolabelled delmopinol to the various strains. Fresh isolates and type strains of gram-negative rods associated with periodontal disease, Porphyromonas gingivalis, Prevotella intermedia, Actinobacillus actinomycetemcomitans, and strains of the gram-positive streptococci Streptococcus sanguis, Streptococcus mutans and Streptococcus salivarius, were exposed to 3.2 mM (0.1%) or 6.4 mM (0.2%) delmopinol hydrochloride from 1 to 90 min. For electron microscopy the cells were fixed and negatively contrast-stained. Treatment with 6.4 mM delmopinol for 1 min resulted in marked ultrastructural changes of cell wall components and the outer cell membrane of the 3 gram-negative species compared with control cells, whereas the gram-positive streptococci treated with delmopinol showed little or no morphologic alteration as compared with untreated cells. The result from the electron microscopy was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins released from bacterial cells treated as for electron microscopy. More material was extracted from the gram-negative rods than from the gram-positive cocci. Significantly more delmopinol bound to the gram-negative rods than to the streptococci. It appears that the amphiphilic properties of delmopinol make gram-negative rods more vulnerable to delmopinol than gram-positive streptococci.

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.

[Ultrastructure and properties of Actinobacillus actinomycetemcomitans]

In this study, plaque samples taken from periodontal pockets were cultured on Tryptic-soy-serum-bacitracin-vancomycin agar and identified according to colony morphology, Gram stain, catalase reaction and nitrate reduction tests after an incubation of 48 hours in candle jar. Cells identified as Actinobacillus actinomycetemcomitans were evaluated under the transmission electron microscope for fine structure. Outer membrane was observed as an irregular structure containing microcapsules. Unlike previous studies, periplasmic space was observed separately from other layers. Cytoplasmic membrane was observed surrounded by an electron-opaque cytoplasm. Besides, extracellular vesicles were seen extending to the outer environment around cytoplasmic membrane. Pathogenic properties of organelles were discussed. As a result, it was concluded that, in the future studies, products released and structural alterations occurring during growth of the organism, their pathologic effects and ways to suppress them need to be investigated microbiologically, ultrastructurally and biochemically.

Demonstration of the glycocalyces associated with three oral gram-negative bacterial species using a modern acrylic resin technique

The complex highly hydrated chemical composition of the bacterial glycocalyx renders it difficult to preserve and visualize at the ultrastructural level. Polyanionic stains such as ruthenium red help to maintain some structural integrity, and other more modern approaches include antibody stabilization, lectins, and the addition of lysine to the primary fixative. It has been suggested that the glycocalyx of certain disease-associated organisms may play a role in the pathogenesis of some microbially based diseases such as periodontitis. New, more adequate, modern methodologies are therefore required for the further study of this structure. In the present study a cold dehydration process in conjunction with LR white acrylic resin has been employed to study the glycocalyces of three oral gram-negative bacterial species reported to be periodontopathogens. When compared with organisms processed conventionally and with ruthenium red, the organisms processed by the cold dehydration and LR white method demonstrated a fibrous matrix that was not seen in the other specimens. These results indicate that a combination of reduced dehydration temperature and cold acrylic resin embedding provides the best methodology for the visualization of the fine structure of the bacterial glycocalyx. This approach may be particularly useful in the study of organisms within specific disease-associated environments such as the periodontal pocket.

A preliminary study on the effects of the Nd:YAG laser on root surfaces and subgingival microflora in vivo

The purpose of this study was to examine the effects of root preparation using the pulsed Nd:YAG laser, either alone or in combination with manual instrumentation. Study specimens consisting of 18 teeth with associated periodontal pockets from 8 different patients were treated as follows: 5 specimens were root planed with curets followed by laser exposure for 3 minutes using energy settings of 3.0 W at 20 pps; 2 specimens were root planed and then laser treated for 3 minutes using settings of 2.25 W and 20 pps; 4 specimens were treated by laser for 1 minute at settings of 1.75 W and 20 pps followed by root planing; 4 specimens were treated by laser only for 1 minute using settings of 1.75 W and 20 pps; and the remaining 3 teeth served as untreated controls. Both prior to and after completion of the laser and root planing treatments, microbiological samples were obtained from the treated pockets and submitted to a commercial laboratory for analysis of levels of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Prevotella intermedia. With the exception of two 7-day specimens, all others were extracted immediately post-therapy and processed for SEM examination. All treated specimens, regardless of treatment sequence, exhibited some degree of laser-induced root surface alteration. Notably, laser-treated calculus deposits were free of their characteristic surface layer of microbial plaque. Microbial sampling indicated a post-therapy reduction in levels of all 3 putative microbial pathogens compared to pre-treatment samples and control specimens. However, SEM examination revealed residual deposits of plaque and calculus in all treatment groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Electron immunocytochemical localization of Actinobacillus actinomycetemcomitans leukotoxin

The Actinobacillus actinomycetemcomitans leukotoxin was localized in A. actinomycetemcomitans bacteria using an electron immunocytochemical thin-section labeling method. An immuno-dot blot procedure was initially used to ascertain the optimal specimen fixation. This consisted of a periodate-lysine-paraformaldehyde (2%) fixative in a phosphate buffer followed by embedding in LR White. Affinity-purified toxin was used to produce a monospecific polyclonal antibody. The reaction sites were visualized with a colloidal gold-tagged reporter antibody. The leukotoxin was found to be localized either in the cell envelope and/or in membranous vesicles on the outer surface of the bacterial cell. These results support previous observations indicating the same location.