bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental periodontal disease in rats induced by plaque‐forming microorganisms
Authors: van der Hoeven J. S. , Mikx F. H. M. , Plasschaert A. J. M. , Maltha J. C. 
Published: June 2006

Three different capsule or extracellular slime producing microorganisms: Rothia, Neisseria and Bacterionema were tested in SPF Osborne‐Mendel rats for their ability to stimulate plaque formation and their effect on the gingiva. Gingival inflammation in the rats was evaluated in histological sections of buccal gingivae.All three the test strains were found to stimulate plaque formation. The high plaque score in the inoculated groups of rats was found to be attended by an increase in the area of infiltrated gingival tissue.
Cellular response to subgingival injection of bacterial products in the rat
Authors: Irving J. T. , Heeley J. D. , Socransky S. S. 
Published: June 2006

Various bacterial products were injected in the oral mucosa of 74 conventional weanling rats of the Holtzman strain. The site of injection was lingual to the mesial cusp of the first molar of the maxilla or mandible. The bacterial products were whole dead cells, cell walls or cytoplasm obtained from Actinomyces naeslundii. Saline was injected into control animals. The animals were killed at intervals 0 to 48 hours subsequently, and the tissues examined by standard histological methods.In all cases there was an initial polymorphonuclear response at the site of injection which had usually disappeared by 24 hours. In addition, osteoblasts on the adjacent alveolar bone were destroyed and in no case had they reappeared at 48 hours. Osteocytes were also missing after whole dead cell or cytoplasm injections, but not after cell wall injections. The most striking difference between the various reactions was an early appearance of lymphocytes after cell wall injections, which overshadowed the polymorphonuclear response, and which persisted up to 24 hours post injection. The disappearance of osteoblasts and osteocytes after injection of bacterial products from an organism associated with periodontal disease in man may explain in part the bone loss in this condition.
Two years oral use of chlorhexidine in man
Authors: Löue Harald , Rindom Schiöutt C. , Glavind L. , Karring T. 
Published: June 2006

The general objectives of this study were to examine the long term effects of daily chlorhexidine application on the development of dental plaque, calculus and periodontal pathology and to monitor changes in oral microbiology and any systemic or local side effects following prolonged use of chlorhexidine over a period of two years.An experimental group of 61 medical and dental students used 10 ml. of 0.2 per cent aqueous solution of chlorhexidine gluconate daily in addition to tooth brushing and interdental cleansing. A control group of 59 students used a placebo solution in addtion to tooth brushing and interdental cleansing. Assessment of selected oral and systemic parameters took place at regular intervals throughout the experiment.The results show that, when compared to the placebo solution, chlorhexidine treatment reduced plaque and gingivitis, but tended to stain teeth. Stains were readily removed by a conventional dental prophylaxis procedure. The chlorhexidine group tended to exhibit a greater amount of supragingival calculus. There were no other local side effects relative to the structure and function of the oral mucosa, tongue, salivary glands and pharyngeal complex, following the prolonged use of chlorhexidine.
Two years oral use of chlorhexidine in man
Authors: Mackenzie I. C. , Nuki K. , Löue H. , Rindom Schiöutt C. 
Published: June 2006

Possible changes in the structure of human oral mucosa resulting from exposure to chlorhexidine were examined in biopsy specimens of palatal and gingival mucosa obtained from three groups of young adults who had rinsed for more than 1 year (a) once or (b) twice daily with 0.2 % chlorhexidine solution or (c) with a placebo mouthwash. Specimens were quenched in liquid nitrogen and cryostat sectioned perpendicular to the epithelial surface. Sections stained with hematoxylin and eosin were used to assess the degree of keratinization of epithelia and to measure the width of the stratum corneum. Sections treated with buffered alkaline solutions were used to expand and count the number of layers of cells in the stratum corneum.All specimens examined showed evidence of keratinization and, in keeping with previous reports, palatal specimens were more frequently orthokeratinized than gingival specimens. Mean width of the stratum corneum of gingival specimens was approximately 13 μm and of palatal specimens, 23 μm. The mean number of layers of cells in the stratum corneum of the gingiva was approximately 10 and of the palate, approximately 12. Differences in the degree of keratinization and thickness of the stratum corneum between gingival and palatal specimens was statistically significant, but no statistically significant differences were found between the chlorhexidine‐exposed and non‐chlorhexidine‐exposed palatal tissue in keratinization, layers of cells or thickness of the stratum corneum. Neither was there any statistical difference in the same parameters for the gingival specimens. The methods employed did not therefore detect any changes in the normal structure of keratinizing oral epithelia as a result of prolonged daily exposure to chlorhexidine.
Initial gingivitis induced by topical application of plaque extract
Authors: Kahnberg K‐E. , Lindhe J. , Helldén L. 
Published: June 2006

The present study was undertaken to examine if soluble substances in human dental plaque were able to induce structural alterations in the marginal gingiva characteristic of initial gingival inflammation.Four‐day old plaque was sampled from dental students; the plaque material was pooled, suspended in saline, homogenized, centrifuged and filtered. The supernatant, the plaque‐extract, was then, during an eight hour period, topically applied to the gingival margin of the upper jaws of five Beagle dogs. In control regions saline was applied in an identical manner. One and a half hour before sacrifice the animals were given i.v. injections of colloidal carbon.Biopsies of test and control regions were taken according to a technique described by Schroeder et al (1973). The biopsy specimens were embedded in Epon. Semithin sections (2‐3 μm) were examined in the microscope regarding 1. amount of vascular units subjacent to the junctional epithelium containing carbon particles2. number of polymorphonuclear and mononuclear leucocytes within the junctional epithelium.The examinations revealed that the gingival units exposed to plaque extract in comparison to controls harboured larger numbers of carbon labelled vascular units and larger numbers of leukocytes within the junctional epithelium. The data also showed that the main reaction occurred in the marginal portion of the gingival tissue. The observations of this study indicate that soluble substances from human dental plaque when applied topically in the gingival sulcus may give rise to structural alterations similar to those developing in the gingival tissues in response to plaque accumulation.
Role of bacterial products in periodontitis
Authors: Johnson David A. , Chen Chen‐Lo H. , Dombrowski John C. , Nowotny Alois 
Published: June 2006

Since the two major theories assume that either a hypersensitivity to plaque immunogens or a direct tissue damage caused by plaque constituents plays the dominant role in the etiology of periodontitis, we first investigated the nature of the immune response to and the endotoxin content of human plaque.It was found that pooled human plaque samples contained a very low but significant level of endotoxin, as determined by phenol‐water extraction, by pyrogenicity in New Zealand white rabbits, by local Shwartzman skin test, and by the Limulus lysate assay.A measurable humoral immune response could be elicited by human plaque material if injected into guinea pigs intraperitoneally. Intragingival application of the same material was a less efficient route of immunization. This humoral immune response was measured by passive hemagglutination and immune counterelectrophoresis.Cell‐mediated immune response, as measured by skin sensitivity, lymphoblast transformation and rosette formation assays in guinea pigs, sensitized either intragingivally or intraperitoneally, gave diverse results. No cell‐mediated immune response could be detected by using the lymphoblast transformation assay. A weak but positive reaction could be elicited in one‐third to one‐half of the sensitized animals by injecting them intradermally or by testing rosette formation of their spleen cells with plaque‐coated sheep erythrocytes.The weak and inconsistent results do not rule out the possibility that cell‐mediated immune responses and their mediators cause human periodontitis, but they make us cautious in considering such events as the sole factors in the development of the disease. As of now, we have even less reason to exclude the possibility that certain types of immune responses to plaque protect the patient from periodontitis.
Kinematic structure in the young σ Orionis association
Authors: Jeffries R. D. , Maxted P. F. L. , Oliveira J. M. , Naylor Tim 
Published: June 2006

Abstract
We have used precise radial velocity measurements for a large number of candidate low-mass stars and brown dwarfs to show that the young σ Ori ‘cluster’ consists of two spatially superimposed components which are kinematically separated by 7 km s−1 in radial velocity, and which have different mean ages. We examine the relationship of these two kinematic groups to other populations in the Orion OB1 association, and briefly discuss the consequence of mixed age samples for ongoing investigations of the formation and evolution of low-mass objects in this much-observed region.
Canals in Milky Way radio polarization maps
Authors: Fletcher A. , Shukurov A. 
Published: June 2006

Abstract
Narrow depolarized canals are common in maps of the polarized synchrotron emission of the Milky Way. Two physical effects that can produce these canals have been identified: the presence of Faraday rotation measure (RM) gradients in a foreground screen, and the cumulative cancellation of polarization known as differential Faraday rotation. We show that the behaviour of the Stokes parameters Q and U in the vicinity of a canal can be used to identify its origin. In the case of canals produced by a Faraday screen we demonstrate that, if the polarization angle changes by 90° across the canal, as is observed in all fields to-date, the gradients in RM must be discontinuous. Shocks are an obvious source of such discontinuities and we derive a relation of the expected mean separation of canals to the abundance and Mach number of supernova-driven shocks, and compare this with recent observations by Haverkorn, Katgert & de Bruyn. We also predict the existence of less common canals with polarization angle changes other than 90°. Differential Faraday rotation can produce canals in a uniform magneto-ionic medium, but as the emitting layer becomes less uniform the canals will disappear. We show that for moderate differences in emissivity in a two-layer medium, of up to 1/2, and for Faraday depth fluctuations of standard deviation ≲1 rad, canals produced by differential rotation will still be visible.
The Effect of Vortex Formation on Left Ventricular Filling and Mitral
Valve Efficiency
Authors: Pierrakos Olga , Vlachos Pavlos P. 
Published: June 2006

Abstract
A new mechanism for quantifying the filling energetics in the left ventricle (LV) and past mechanical heart valves (MHV) is identified and presented. This mechanism is attributed to vortex formation dynamics past MHV leaflets. Recent studies support the conjecture that the natural healthy left ventricle (LV) performs in an optimum, energy-preserving manner by redirecting the flow with high efficiency. Yet to date, no quantitative proof has been presented. The present work provides quantitative results and validation of a theory based on the dynamics of vortex ring formation, which is governed by a critical formation number (FN) that corresponds to the dimensionless time at which the vortex ring has reached its maximum circulation content, in support of this hypothesis. Herein, several parameters (vortex ring circulation, vortex ring energy, critical FN, hydrodynamic efficiencies, vortex ring propagation speed) have been quantified and presented as a means of bridging the physics of vortex formation in the LV. In fact, the diastolic hydrodynamic efficiencies were found to be 60, 41, and 29%, respectively, for the porcine, anti-anatomical, and anatomical valve configurations. This assessment provides quantitative proof of vortex formation, which is dependent of valve design and orientation, being an important flow characteristic and associated to LV energetics. Time resolved digital particle image velocimetry with kilohertz sampling rate was used to study the ejection of fluid into the LV and resolve the spatiotemporal evolution of the flow. The clinical significance of this study is quantifying vortex formation and the critical FN that can potentially serve as a parameter to quantify the LV filling process and the performance of heart valves.
Frequency Response of a Viscoelastic Tensegrity Model: Structural Rearrangement Contribution to Cell Dynamics
Authors: Cañadas Patrick , Wendling-Mansuy Sylvie , Isabey Daniel 
Published: June 2006

Abstract
In an attempt to understand the role of structural rearrangement onto the cell response during imposed cyclic stresses, we simulated numerically the frequency-dependent behavior of a viscoelastic tensegrity structure (VTS model) made of 24 elastic cables and 6 rigid bars. The VTS computational model was based on the nonsmooth contact dynamics (NSCD) method in which the constitutive elements of the tensegrity structure are considered as a set of material points that mutually interact. Low amplitude oscillatory loading conditions were applied and the frequency response of the overall structure was studied in terms of frequency dependence of mechanical properties. The latter were normalized by the homogeneous properties of constitutive elements in order to capture the essential feature of spatial rearrangement. The results reveal a specific frequency-dependent contribution of elastic and viscous effects which is responsible for significant changes in the VTS model dynamical properties. The mechanism behind is related to the variable contribution of spatial rearrangement of VTS elements which is decreased from low to high frequency as dominant effects are transferred from mainly elastic to mainly viscous. More precisely, the elasticity modulus increases with frequency while the viscosity modulus decreases, each evolution corresponding to a specific power-law dependency. The satisfactorily agreement found between present numerical results and the literature data issued from in vitro cell experiments suggests that the frequency-dependent mechanism of spatial rearrangement presently described could play a significant and predictable role during oscillatory cell dynamics.
The
Brucella abortus
Cyclic β-1,2-Glucan Virulence Factor Is Substituted with O-Ester-Linked Succinyl Residues
Authors: Roset Mara S. , Ciocchini Andrés E. , Ugalde Rodolfo A. , Iñón de Iannino Nora 
Published: June 2006

ABSTRACT

Brucella
periplasmic cyclic β-1,2-glucan plays an important role during bacterium-host interaction. Nuclear magnetic resonance spectrometry analysis, thin-layer chromatography, and DEAE-Sephadex chromatography were used to characterize
Brucella abortus
cyclic glucan. In the present study, we report that a fraction of
B. abortus
cyclic β-1,2-glucan is substituted with succinyl residues, which confer anionic character on the cyclic β-1,2-glucan. The oligosaccharide backbone is substituted at C-6 positions with an average of two succinyl residues per glucan molecule. This O-ester-linked succinyl residue is the only substituent of
Brucella
cyclic glucan. A
B. abortus
open reading frame (BAB1_1718) homologous to
Rhodobacter sphaeroides
glucan succinyltransferase (OpgC) was identified as the gene encoding the enzyme responsible for cyclic glucan modification. This gene was named
cgm
for
c
yclic
g
lucan
m
odifier and is highly conserved in
Brucella melitensis
and
Brucella suis
. Nucleotide sequencing revealed that
B. abortus cgm
consists of a 1,182-bp open reading frame coding for a predicted membrane protein of 393 amino acid residues (42.7 kDa) 39% identical to
Rhodobacter sphaeroides
succinyltransferase.
cgm
null mutants in
B. abortus
strains 2308 and S19 produced neutral glucans without succinyl residues, confirming the identity of this protein as the cyclic-glucan succinyltransferase enzyme. In this study, we demonstrate that succinyl substituents of cyclic β-1,2-glucan of
B. abortus
are necessary for hypo-osmotic adaptation. On the other hand, intracellular multiplication and mouse spleen colonization are not affected in
cgm
mutants, indicating that cyclic-β-1,2-glucan succinylation is not required for virulence and suggesting that no low-osmotic stress conditions must be overcome during infection.
An Unstable Competence-Induced Protein, CoiA, Promotes Processing of Donor DNA after Uptake during Genetic Transformation inStreptococcus pneumoniae
Authors: Desai Bhushan V. , Morrison Donald A. 
Published: June 2006

ABSTRACTNatural genetic transformation inStreptococcus pneumoniaeentails transcriptional activation of at least two sets of genes. One set of genes, activated by the competence-specific response regulator ComE, is involved in initiating competence, whereas a second set is activated by the competence-specific alternative sigma factor ComX and functions in DNA uptake and recombination. Here we report an initial characterization of CoiA, a ComX-dependent gene product that is induced during competence and is required for transformation. CoiA is widely conserved among gram-positive bacteria, and in streptococci, the entirecoiAlocus composed of four genes is conserved. By use of immunoblot assay, we show that, similar to its message, CoiA protein is transient, appearing at 10 min and largely disappearing by 30 min post-competence induction. Using complementation analysis, we establish thatcoiAis the only gene of this induced locus needed for transformability. We find no indication of CoiA having a role in regulating competence. Finally, using32P- and3H-labeled donor DNA, we demonstrate that acoiAmutant can internalize normal amounts of donor DNA compared to the wild-type strain but is unable to process it into viable transformants, suggesting a role for CoiA after DNA uptake, either in DNA processing or recombination.
Regulation of theHelicobacter pyloriFe-S Cluster Synthesis Protein NifS by Iron, Oxidative Stress Conditions, and Fur
Authors: Alamuri Praveen , Mehta Nalini , Burk Andrew , Maier Robert J. 
Published: June 2006

ABSTRACTTranscription of both chromosomal and extrachromosomally introducednifSwas regulated (up-expressed) by oxygen or by supplemental iron conditions. This up-expression was not observed in afurmutant strain background or when an iron chelator was added. Iron-bound Fur (but not apo-Fur) recognized thenifSpromoter, and Fur bound significantly farther upstream (−155 bp to −190 bp and −210 to −240 bp) in the promoter than documentedHelicobacter pyloriFur binding regions. This binding was stronger than Fur recognition of theflgEornapApromoter and includes a Fur recognition sequence common to theH. pylori pfrandsodBupstream areas. Studies of Fur-regulated genes inH. pylorihave indicated that apo-Fur acts as a repressor, but our results demonstrate that iron-bound Fur activates (nifS) transcription.
Mutational Analysis of the Flagellar Rotor Protein FliN: Identification of Surfaces Important for Flagellar Assembly and Switching
Authors: Paul Koushik , Harmon Jacob G. , Blair David F. 
Published: June 2006

ABSTRACTFliN is a component of the flagellar switch complex in many bacterial species. The crystal structure is known for most of FliN, and a targeted cross-linking study (K. Paul and D. F. Blair, J. Bacteriol. 188:2502-2511, 2006) showed that it is organized in ring-shaped tetramers at the bottom of the basal body C ring. FliN is essential for flagellar assembly and direction switching, but its precise functions have not been defined. Here, we identify functionally important regions on FliN by systematic mutagenesis. Nonconservative mutations were made at positions sampling the surface of the protein, and the effects on flagellar assembly and function were measured. Flagellar assembly was disrupted by mutations in a conserved hydrophobic patch centered on the dimer twofold axis or by mutations on the surface that forms the dimer-dimer interface in the tetramer. The assembly defect in hydrophobic-patch mutants was partially rescued by overexpression of the flagellar export proteins FliH and FliI, and coprecipitation assays demonstrated a binding interaction between FliN and FliH that was weakened by mutations in the hydrophobic patch. Thus, FliN might contribute to export by providing binding sites for FliH or FliH-containing complexes. The region around the hydrophobic patch is also important for switching; certain mutations in or near the patch caused a smooth-swimming chemotaxis defect that in most cases could be partially rescued by overexpression of the clockwise-signaling protein CheY. The results indicate that FliN is more closely involved in switching than has been supposed, possibly contributing to the binding site for CheY on the switch.
Biochemical and Molecular Characterization of a Na
+
-Translocating F
1
F
o
-ATPase from the Thermoalkaliphilic Bacterium
Clostridium paradoxum
Authors: Ferguson Scott A. , Keis Stefanie , Cook Gregory M. 
Published: June 2006

ABSTRACT

Clostridium paradoxum
is an anaerobic thermoalkaliphilic bacterium that grows rapidly at pH 9.8 and 56°C. Under these conditions, growth is sensitive to the F-type ATP synthase inhibitor
N
,
N′
-dicyclohexylcarbodiimide (DCCD), suggesting an important role for this enzyme in the physiology of
C. paradoxum
. The ATP synthase was characterized at the biochemical and molecular levels. The purified enzyme (30-fold purification) displayed the typical subunit pattern for an F
1
F
o
-ATP synthase but also included the presence of a stable oligomeric
c
-ring that could be dissociated by trichloroacetic acid treatment into its monomeric
c
subunits. The purified ATPase was stimulated by sodium ions, and sodium provided protection against inhibition by DCCD that was pH dependent. ATP synthesis in inverted membrane vesicles was driven by an artificially imposed chemical gradient of sodium ions in the presence of a transmembrane electrical potential that was sensitive to monensin. Cloning and sequencing of the
atp
operon revealed the presence of a sodium-binding motif in the membrane-bound
c
subunit (viz., Q
28
, E
61
, and S
62
). On the basis of these properties, the F
1
F
o
-ATP synthase of
C. paradoxum
is a sodium-translocating ATPase that is used to generate an electrochemical gradient of Na
+
that could be used to drive other membrane-bound bioenergetic processes (e.g., solute transport or flagellar rotation). In support of this proposal are the low rates of ATP synthesis catalyzed by the enzyme and the lack of the C-terminal region of the ε subunit that has been shown to be essential for coupled ATP synthesis.