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Biomedical subjects

R Legrand

Publications and source records attributed to R Legrand.

At least 19 recordsLinked to original sources
PubMed2000

Novel mechanism of beta-lactam resistance due to bypass of DD-transpeptidation in Enterococcus faecium.

The peptidoglycan structure of in vitro selected ampicillin-resistant mutant Enterococcus faecium D344M512 and of the susceptible parental strain D344S was determined by reverse phase high performance liquid chromatography and mass spectrometry. The muropeptide monomers were almost identical in the two strains. The substantial majority (99.3%) of the oligomers from the susceptible strain D344S contained the usual d-alanyl --> d-asparaginyl (or d-aspartyl)-l-lysyl cross-link (d-Ala --> d-Asx-l-Lys) generated by beta-lactam-sensitive DD-transpeptidation. The remaining oligomers (0.7%) were produced by beta-lactam-insensitive LD-transpeptidation, because they contained l-Lys --> d-Asx-l-Lys cross-links. The muropeptide oligomers of the ampicillin-resistant mutant D344M512 contained only these l-Lys --> d-Asx-l-Lys cross-links indicating that resistance was due to the bypass of the beta-lactam-sensitive DD-transpeptidation reaction. The discovery of this novel resistance mechanism indicates that DD-transpeptidases cannot be considered anymore as the sole essential transpeptidase enzymes.

Amino Acid Sequence↗
PubMed2000

Vancomycin resistance is associated with serine-containing peptidoglycan in Enterococcus gallinarum.

In Enterococcus gallinarum SC1, a low-level vancomycin-resistant strain, only monomeric muropentapeptides with a C-terminal D-alanine were detected after growth without vancomycin. In contrast, in SC1 induced by vancomycin, as well as in AIB39, a constitutive vancomycin-resistant strain, monomeric and dimeric muropentapeptides with a C-terminal D-serine were detected.

Anti-Bacterial Agents↗
PubMed2000

Effect of nicotine on rat gingival fibroblasts in vitro.

Tobacco smoking is considered a major risk factor for the development and progression of periodontal diseases (Haber, J. and Wattles, J. (1994). J. Periodontol., 64, 16-23). The purpose of this study was to determine the effects of nicotine on rat gingival fibroblasts (RGF) cultured in vitro. After ether anesthesia, rat gingival tissues were obtained from the attached gingiva of a Wistar rat. Small fragments of gingiva were maintained in culture in Petri dishes. Fibroblasts developing from these explants were collected to obtain monolayer cultures. After the fourth passage (T4), cells were supplemented with nicotine at various concentrations. Control and treated cells were examined under phase contrast or transmission electron microscopy. They were compared as regards their DNA content, mitochondrial activity, collagen and protein synthesis, and cell death by apoptosis or necrosis. Nicotine from 0.05 microM to 1 mM did not affect the DNA content or protein and collagen synthesis. At concentrations between 3 and 5 mM, growth was significantly diminished and the survival rate reduced. Ultrastructural analysis revealed dilated mitochondria and vacuolization in treated cells, suggestive of necrosis, but increased apoptosis was also revealed by cytometry. On the basis of this in vitro study, it appears that tobacco, through its component nicotine, may directly affect various functions of RGF.

Animals↗
PubMed1999

Evolving smarts.

Explore the source record for details and available documents.

Humans↗
PubMed1999

Oral status and nutrition in the institutionalized elderly.

OBJECTIVES: To evaluate, in an elderly population, whether poor oral status might be a contributing factor to the development of undernutrition and might be associated with less eating pleasure, more subjective eating difficulty and increased mashed food consumption. METHODS: An oral examination and an evaluation of masticatory capacity were performed on 120 institutionalized elderly subjects. The nutritional assessment included serum albumin concentration, the Mini Nutritional Assessment and a questionnaire on eating habits. RESULTS: Edentulous subjects without dentures or with only one complete denture had significantly lower MNA scores than edentulous subjects with two complete dentures (p < 0.05). Edentulous subjects with two complete dentures more frequently reported taking pleasure from eating (p = 0.05), and had less frequent difficulties with hard foods (p = 0.01) than edentulous subjects without dentures or with only one complete denture. Mashed food consumption (p < 0.01) was also reported more frequently in edentulous subjects without dentures or with only one complete denture. Subjects with two complete dentures had similar or better MNA scores as dentate subjects with relatively few remaining teeth (10.4 +/- 7.8 teeth). About half of the subjects (53%) could not perform the masticatory test. These subjects had lower MNA scores (p = 0.001) and a larger proportion ate mashed food (p < 0.001) compared to those who were able to perform the test. CONCLUSIONS: Poor oral status (edentulous without dentures or with only one complete denture) increased difficulty in eating hard foods, increased mashed food consumption and decreased eating pleasure. It seemed also to put institutionalized subjects at higher risk of undernutrition.

Aged↗
PubMed1999

The combined use of bioresorbable membranes and xenografts or autografts in the treatment of bone defects around implants. A study in beagle dogs.

The aim of the present investigation was to test the effect of a bioresorbable membrane supported by xenografts or autografts in regenerating bone into peri-implant defects. In 3 dogs, the mandibular premolars P2, P3, P4 and M1 were extracted bilaterally. After 4 months of healing, 3 standardized bone defects were prepared on each side of the mandible and 1 implant per defect was placed. The 6 sites in each dog were distributed into 4 different treatment groups: 2 sites received a Bio-Gide membrane alone (BG); 2 sites received a Bio-Gide membrane supported by Bio-Oss (BG + BO); 1 site received the Bio-Gide membrane supported by autogenic bone harvested from the prepared defects (BG + Aut); 1 site received neither membrane nor bone graft and served as control (C). The soft tissue flaps were adapted and sutured for primary healing. No adverse events occurred during the experimental period. After 16 weeks, the dogs were sacrificed and histomorphometric examinations on non-decalcified ground sections were carried out. The vertical bone growth amounted to 45% (SD +/- 13%) of the defect height in the BG group, to 78% (SD +/- 29%) in the BG + BO group, to 69% (SD +/- 9%) in the BG + Aut group, and to 22% (SD +/- 10%) in C group. The horizontal bone growth measured 78% (SD +/- 16%) in the BG group, 81% (SD +/- 21%) in the BG + BO group, 82% (SD +/- 12%) in the BG + Aut group, and 46% (SD +/- 21%) in the C group. The vertical height of bone growth in contact with the implant measured 17% (SD +/- 12%) in the BG group, 20% (SD +/- 12%) in the BG + BO group, 17% (SD +/- 7%) in the BG + Aut group, and 12% (SD +/- 8%) in the C group. The surface fraction of the graft in direct bone contact measured 89% (SD +/- 9%) in the BG + BO group and 93% (SD +/- 3%) in the BG + Aut group. It is concluded that the bioresorbable membrane tested enhances bone regeneration, in particular in conjunction with the use of a supporting graft material. In addition, deproteinized bovine bone mineral and autogenic bone grafts appeared to be equally well integrated into regenerating bone. Finally, no additional effects in the bone growth was observed with the autogenous bone in comparison with the hydroxyapatite.

Absorbable Implants↗
PubMed1999

Interspecies complementation in Saccharopolyspora erythraea : elucidation of the function of oleP1, oleG1 and oleG2 from the oleandomycin biosynthetic gene cluster of Streptomyces antibioticus and generation of new erythromycin derivatives.

Two glycosyltransferase genes, oleG1 and oleG2, and a putative isomerase gene, oleP1, have previously been identified in the oleandomycin biosynthetic gene cluster of Streptomyces antibioticus. In order to identify which of these two glycosyltransferases encodes the desosaminyltransferase and which the oleandrosyltransferase, interspecies complementation has been carried out, using two mutant strains of Saccharopolyspora erythraea, one strain carrying an internal deletion in the eryCIII (desosaminyltransferase) gene and the other an internal deletion in the eryBV (mycarosyltransferase) gene. Expression of the oleG1 gene in the eryCIII deletion mutant restored the production of erythromycin A (although at a low level), demonstrating that oleG1 encodes the desosaminyltransferase required for the biosynthesis of oleandomycin and indicating that, as in erythromycin biosynthesis, the neutral sugar is transferred before the aminosugar onto the macrocyclic ring. Significantly, when an intact oleG2 gene (presumed to encode the oleandrosyltransferase) was expressed in the eryBV deletion mutant, antibiotic activity was also restored and, in addition to erythromycin A, new bioactive compounds were produced with a good yield. The neutral sugar residue present in these compounds was identified as L-rhamnose attached at position C-3 of an erythronolide B or a 6-deoxyerythronolide B lactone ring, thus indicating a relaxed specificity of the oleandrosyltransferase, OleG2, for both the activated sugar and the macrolactone substrate. The oleP1 gene located immediately upstream of oleG1 was likewise introduced into an eryCII deletion mutant of Sac. erythraea, and production of erythromycin A was again restored, demonstrating that the function of OleP1 is identical to that of EryCII in the biosynthesis of dTDP-D-desosamine, which we have previously proposed to be a dTDP-4-keto-6-deoxy-D-glucose 3, 4-isomerase.

Chromatography, High Pressure Liquid↗
PubMed1999

Graft of autologous fibroblasts in gingival tissue in vivo after culture in vitro. Preliminary study on rats.

Several grafting techniques and guided tissue regeneration techniques (GTR) have been well-developed in periodontal surgery. However, these techniques could induce pain and side effects, such as a gingival recession during the healing period following the therapy. The graft of a small autologous connective tissue, using non-invasive surgical techniques could yield several benefits for the patients. Our preliminary study explores the feasibility of collecting healthy gingival tissues, culturing them in vitro to amplify rat gingival fibroblasts (RGF) and inoculating the obtained cells into autologous rat gingival tissues in vivo. Gingival tissues samples were cultured as explants as described by Freshney et al. and Adolphe. Confluent cells surrounding explants were detached after 7 d of culture from Petri dishes using 0.05% trypsin and designated "first transferred cells" (T1). At the third passage (T3), cells cultured as monolayer were either examined under microscopy--phase contrast, scanning, or transmission electron--or numerated after trypan blue exclusion test. Autologous RGF labelled with fluorochrome were inoculated at the vestibular and palatine site of gingival tissue close to the superior incisors. In this preliminary study, 12 Wistar rats were used; for each, 2 biopsies were dissected and fixed for phase contrast or fluorescence microscopy. On d 1, 3 and 7 after injection in rat gingival tissues, fluorochrome-labelled cells could be detected in all these.

Animals↗
PubMed1999

Culture of gingival fibroblasts on bioabsorbable regenerative materials in vitro.

BACKGROUND: The use of membranes in guided tissue regeneration (GTR) can limit the apical migration of gingival cells and favor the establishment of new attachment by periodontal ligament fibroblasts. However, gingival recession during healing following GTR has been described as a frequent complication. The purpose of this study was to determine if gingival fibroblasts are affected by the composition of the bioabsorbable membranes used in mucogingival surgery. METHODS: Two type of bioabsorbable regenerative materials were used as cell carriers. Wistar rat gingival fibroblasts (RGF) were obtained from attached gingiva, cut into small fragments, and placed in culture dishes. When confluent, cells were detached using trypsin and identified as "first transferred cells" (P1). At the third passage (P3), cell count, trypan blue exclusion test, acid phosphatase activity, DNA synthesis, phase contrast microscopy, and scanning electron microscopy were performed. The cells were then placed in wells containing the membranes and incubated for 72 hours. RESULTS: When examined under microscopy, the control wells (without membranes) showed one cell type with the elongated appearance characteristic of fibroblasts. The wells with membranes showed an altered cell morphology with a high proportion of cell fragments regardless of the type of membrane used. CONCLUSIONS: These results suggest that cell carrier membranes could affect RGF morphology and thus alter gingival tissue healing following GTR.

Absorbable Implants↗
PubMed1999

[Burning mouth syndrome].

The BMS which involves the oral mucosa and produces sensations of pain and prickling is still poorly known by the physician. It differs from the other pathologies of the oral mucosa by its multifactorial etiology and by its high prevalence among postmenopausal women. The current treatments are somewhat disappointing and postmenopausal women suffering from BMS are advised to take a hormonal replacement therapy even though no direct relation between BMS and estrogen blood levels has been proved.

Burning Mouth Syndrome↗
PubMed1998

Site-directed mutagenesis and chemical modification of the two cysteine residues of the UDP-N-acetylmuramoyl:L-alanine ligase of Escherichia coli.

Site-directed mutagenesis and chemical modification of the two cysteine residues of the MurC L-alanine-adding enzyme from Escherichia coli were undertaken to study their possible role in activity and stability. Their replacement by alanine was not critical for activity. However, C230 played a role in enzyme stability and substrate binding. N-Ethylmaleimide alkylation led to monoalkylated and dialkylated proteins. The monoalkylated protein had mostly unmodified C230 residues. The extent of alkylation of C230 paralleled the loss of activity, whereas that of C426 did not. Protection against inactivation by beta,gamma-imidoadenosine 5'-triphosphate implied the involvement of C230 in the ATP binding site.

Alanine↗
PubMed1998

Acquisition of five high-Mr penicillin-binding protein variants during transfer of high-level beta-lactam resistance from Streptococcus mitis to Streptococcus pneumoniae.

Penicillin-resistant isolates of Streptococcus pneumoniae generally contain mosaic genes encoding the low-affinity penicillin-binding proteins (PBPs) PBP2x, PBP2b, and PBP1a. We now present evidence that PBP2a and PBP1b also appear to be low-affinity variants and are encoded by distinct alleles in beta-lactam-resistant transformants of S. pneumoniae obtained with chromosomal donor DNA from a Streptococcus mitis isolate. Different lineages of beta-lactam-resistant pneumococcal transformants were analyzed, and transformants with low-affinity variants of all high-molecular-mass PBPs, PBP2x, -2a, -2b, -1a, and -1b, were isolated. The MICs of benzyl-penicillin, oxacillin, and cefotaxime for these transformants were up to 40, 100, and 50 microg/ml, respectively, close to the MICs for the S. mitis donor strain. Recruitment of low-affinity PBPs was accompanied by a decrease in cross-linked muropeptides as revealed by high-performance liquid chromatography of muramidase-digested cell walls, but no qualitative changes in muropeptide chemistry were detected. The growth rates of all transformants were identical to that of the parental S. pneumoniae strain. The results stress the potential for the acquisition by S. pneumoniae of high-level beta-lactam resistance by interspecies gene transfer.

Amino Acid Sequence↗
PubMed1998

Evaluation of a diphenylphosphorylazide-crosslinked collagen membrane for guided bone regeneration in mandibular defects in rats.

In the present study, the potential of a diphenylphosphorylazide-crosslinked type I bovine collagen membrane was evaluated in the healing of mandibular bone defects applying the biological concept of guided bone regeneration. The experiment was carried out on 25 Wistar rats. After exposing the mandibular ramus bilaterally, 5 mm diameter full-thickness circular bone defects were surgically created. While the defect on one side was covered by the membrane (experimental), the defect on the other side was left uncovered (control) before closure of the overlying soft tissues. The rats were sacrificed in groups of 5 after 7, 15, 30, 90, and 180 days of healing. Although at early stages of healing similar amounts of bone formation were observed in the experimental and control defects, after 1 month of healing, most of the experimental defects were completely closed with new bone, while in the control defects, only limited amounts of new bone were observed at the rims and in the lingual aspect of the lesions. In the 90- and 180-day animals, all experimental defects were completely closed, while in the control defects, no statistically significant increase in bone regeneration was observed. The increase in percentage of bone regeneration in the experimental defects was statistically significant between the 15-day specimens as compared with the 7-day specimens (P < 0.01) and likewise between 30-day and 15-day specimens (P < 0.001). It can be concluded that a DPPA-crosslinked collagen membrane yields biocompatibility, ad hoc mechanical hindrance, and handling characteristics suitable for guided bone regeneration applications in this experimental model.

Alveolar Bone Loss↗
PubMed1998

[Osseointegrated endosseous implants, University of Liège concepts. Various clinical applications].

Based on fundamental experimental studies performed by the research teams of Professor Bränemark (Göteborg, Sweden), the use of dental implants has become a scientifically accepted treatment concept in Dentistry to replace lost or missing teeth in fully and partially edentulous patients. The use of dental implants was initiated by the discovery that dental implants made of titanium can be anchored in the jawbone with direct bone contact (osseointegration).

Adult↗
PubMed1997

Presence of UDP-N-acetylmuramyl-hexapeptides and -heptapeptides in enterococci and staphylococci after treatment with ramoplanin, tunicamycin, or vancomycin.

Analyses of the peptidoglycan nucleotide precursor contents of enterococci and staphylococci treated with ramoplanin, tunicamycin, or vancomycin were carried out by high-pressure liquid chromatography coupled with mass spectrometry (MS). In all cases, a sharp increase in the UDP-N-actetylmuramoyl-pentapeptide or -pentadepsipeptide pool was observed. Concomitantly, new peptidoglycan nucleotide peptides of higher molecular masses with hexa- or heptapeptide moieties were identified: UDP-MurNAc-pentapeptide-Asp or pentadepsipeptide-Asp in enterococci and UDP-MurNAc-pentapeptide-Gly or -Ala and UDP-MurNAc-pentapeptide-Gly-Gly or -Ala-Gly in staphylococci. These new compounds are derivatives of normal UDP-MurNAc-pentapeptide or -pentadepsipeptide precursors with the extra amino acid(s) linked to the lysine epsilon-amino group as established by various analytical procedures (MS, MS-MS fragmentation, chemical analysis, and digestion with R39 D,D carboxypeptidase). Except for tunicamycin-treated cells, it was not possible to ascertain whether these unusual nucleotides were formed by direct addition of the amino acids to UDP-MurNAc-pentapeptide (or -pentadepsipeptide) or whether they arose by reverse reactions from lipid I intermediates to which the amino acids had been added.

Anti-Bacterial Agents↗
PubMed1997

Peptidoglycan structure of Lactobacillus casei, a species highly resistant to glycopeptide antibiotics.

The structure of the peptidoglycan of Lactobacillus casei ATCC 393, a species highly resistant to glycopeptide antibiotics, was examined. After digestion, 23 muropeptides were identified; monomers represented 44.7% of all muropeptides, with monomer tetrapeptides being the major ones. Fifty-nine percent of the peptidoglycan was O-acetylated. The cross-bridge between D-alanine and L-lysine consisted of one asparagine, although aspartate could be found in minor quantities. Since UDP-MurNAc-tetrapeptide-D-lactate is the normal cytoplasmic precursor found in this species, monomer tetrapeptide-lactate was expected to be found. However, such a monomer was found only after exposure to penicillin, suggesting that penicillin-sensitive D,D-carboxypeptidases were very active in normal growing cells.

Acetylation↗