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Biomedical subjects

P Francois

Publications and source records attributed to P Francois.

At least 19 recordsLinked to original sources
PubMed2006

Control of a cluster of community-associated, methicillin-resistant Staphylococcus aureus in neonatology.

To control an outbreak of community-associated MRSA (CA-MRSA) in a neonatology unit, an investigation was conducted that involved screening neonates and parents, molecular analysis of MRSA isolates and long-term follow-up of cases. During a two-month period in the summer of 2000, Panton-Valentine leukocidin (PVL)-producing CA-MRSA (strain ST5-MRSA-IV) was detected in five neonates. The mother of the index caseshowed signs of mastitis and wound infection and consequently tested positive for CA-MRSA. A small cluster of endemic, PVL-negative MRSA strains (ST228-MRSA-I) occurred in parallel. Enhanced hygiene measures, barrier precautions, topical decolonization of carriers, and cohorting of new admissions terminated the outbreak. Four months after the outbreak, the mother of another neonate developed furunculosis with the epidemic CA-MRSA strain. One infant had persistent CA-MRSA carriage resulting in skin infection in a sibling four years after the outbreak. In conclusion, an epidemic CA-MRSA strain was introduced by the mother of the index case. This spread among neonates and was subsequently transmitted to another mother and a sibling. This is the first report of a successfully controlled neonatology outbreak of genetically distinct PVL-producing CA-MRSA in Europe.

Adult↗
PubMed2001

Development of a French inpatient satisfaction questionnaire.

OBJECTIVE: To develop a brief French-language, generic, self-administered questionnaire to measure inpatient satisfaction. DESIGN: Issues relevant to patients were identified using three open-ended questions designed in accordance with the disconfirmation paradigm. The content of patients' responses was analysed and then supplemented by items taken from published instruments in order to generate a pool of 93 items. Twenty-nine items were selected following a strict procedure. Content validity was judged by comparing the questionnaire to existing instruments. Construct validity was supported by testing specific hypotheses derived from the literature and by performing principal component analysis. Reliability was estimated by calculating Cronbach's alpha. SETTING: A 2200-bed French teaching hospital. SUBJECTS: A mail survey was carried out on a random sample of 1000 inpatients within 2-4 weeks of discharge. Eligible subjects were medical, surgical and obstetrics inpatients who had stayed in the hospital for more than 24 hours. RESULTS: The participation rate (71%) and the completion rate (95%) were indicators of acceptability. There were modest differences between the questionnaire and published instruments (financial aspects, amenities). Construct representation by principal component analysis consisted of six scales which accounted for 58% of the variance in total satisfaction scores. The reliability estimates of internal consistency ranged from 0.67 to 0.86. CONCLUSION: We propose that the self-administered multidimensional inpatient satisfaction questionnaire provided encouraging preliminary psychometric information. This instrument is intended to involve patient feedback in a continuous quality health care improvement strategy.

Adult↗
PubMed2001

In vivo emergence of subpopulations expressing teicoplanin or vancomycin resistance phenotypes in a glycopeptide-susceptible, methicillin-resistant strain of Staphylococcus aureus.

Several reports indicate the emergence of subpopulations resistant to glycopeptides in some clinical isolates of Staphylococcus aureus. While the development of glycopeptide resistance in S. aureus is easily observed in vitro, the in vivo conditions promoting emergence of glycopeptide-resistant subpopulations are unknown. Using a rat model, subcutaneous implants were chronically infected with a methicillin-resistant strain of S. aureus, MRGR3, devoid of a significant (>10(-7)) glycopeptide-resistant subpopulation at 2 mg/L of either teicoplanin or vancomycin. After 3 weeks of infection in antibiotic-untreated animals, subpopulations emerged, growing on agar containing 10 mg/L of either glycopeptide. These subpopulations were detected in all tissue cage fluids containing >7 log cfu/mL at average frequencies of 4 x 10(-5) and 2 x 10(-5) on teicoplanin- and vancomycin-containing agar, respectively. While teicoplanin MICs increased two- to 16-fold, vancomycin MICs increased by less than two-fold. Population analysis and survival kinetic studies of three teicoplanin-selected subclones indicated that transfer from solid to liquid medium conditions decreased expression of teicoplanin resistance in the bacterial population. In Mueller-Hinton broth, >90% of cells remained fully resistant to antibiotic, but did not grow in the presence of teicoplanin for an initial period of at least 6 h. All three teicoplanin-resistant subclones expressed stable teicoplanin resistance with slight cross-resistance to vancomycin after a few transfers on teicoplanin-supplemented agar. These data suggest that some in vivo conditions may lead to selection of S. aureus subpopulations exhibiting decreased glycopeptide susceptibility and growing in the presence of otherwise inhibitory concentrations of these antimicrobial agents.

Anti-Bacterial Agents↗
PubMed2001

Computer algebra for x-ray spectral reconstruction between 6 and 25 MV.

A previously presented algorithm for the reconstruction of bremsstrahlung spectra from transmission data has been implemented into MATHEMATICA. Spectra vectorial algebra has been used to solve the matrix system A * F = T. The new implementation has been tested by reconstructing photon spectra from transmission data acquired in narrow beam conditions, for nominal energies of 6, 15, and 25 MV. The results were in excellent agreement with the original calculations. Our implementation has the advantage to be based on a well-tested mathematical kernel. Furthermore it offers a comfortable user interface.

Models, Theoretical↗
PubMed2000

Identification of plasma proteins adsorbed on hemodialysis tubing that promote Staphylococcus aureus adhesion.

Risk factors for Staphylococcus aureus infections in patients undergoing hemodialysis include underlying disease, material-induced host defects, and the presence of vascular access catheters. To determine the specific contribution of various potentially adsorbed plasma components in promoting S aureus adhesion to shunt tubing during chronic hemodialysis, we quantified their respective amounts by Western immunoblotting and densitometry and estimated their individual adhesion-promoting activities with specific adhesion-modified bacterial mutants. Fibrinogen, which was the only component consistently present in tubing protein extracts from all patients, was adsorbed in significantly higher amounts on predialyzer than on postdialyzer tubing segments. In contrast, fibronectin and von Willebrand factor were irregularly present in patients' tubing, whereas vitronectin or thrombospondin remained undetectable in all samples. The contribution of fibrinogen in promoting S aureus attachment to hemodialysis tubing was demonstrated by (1) the significantly lower adhesion of a cIfA mutant of strain Newman compared with its parent; (2) the increased attachment of strain 8325-4 after complementation with the cloned cIfA gene on the multicopy plasmid pCF4; and (3) the general tendency for strains Newman and 8325-4(pCF4) to express higher attachment on predialyzer compared with postdialyzer tubing segments in relationship with the higher content of fibrinogen on the former material. However, the specific S aureus attachment-promoting activity of both prefilter and postfilter tubing-adsorbed fibrinogen were much lower than that of the native in vitro-adsorbed protein and may reflect masking or inactivation of the in vivo-adsorbed protein by unknown mechanisms.

Adsorption↗
PubMed2000

[Acute Salmonella typhi meningitis in a 25-day-old newborn infant complicated by obstruction of the sylvian artery].

UNLABELLED: Acute Salmonella typhi meningitis is rare in neonates, mostly reported from developing countries with poor socioeconomic conditions. CASE REPORT: A male Caucasian newborn presented with acute Salmonella typhi meningitis at the age of 25 days. His parents had traveled across several African countries under rudimentary hygienic conditions a few months before his birth. Despite early and adapted antibiotic therapy (cefotaxime plus netilmycine), the child developed ischemia in the region of the left sylvian artery. CONCLUSION: Salmonella meningitis must be considered while dealing with a sick newborn whose mother has traveled across countries with endemic typhoid.

Brain Ischemia↗
PubMed2000

Heterologously expressed Staphylococcus aureus fibronectin-binding proteins are sufficient for invasion of host cells.

Staphylococcus aureus invasion of mammalian cells, including epithelial, endothelial, and fibroblastic cells, critically depends on fibronectin bridging between S. aureus fibronectin-binding proteins (FnBPs) and the host fibronectin receptor integrin alpha(5)beta(1) (B. Sinha et al., Cell. Microbiol. 1:101-117, 1999). However, it is unknown whether this mechanism is sufficient for S. aureus invasion. To address this question, various S. aureus adhesins (FnBPA, FnBPB, and clumping factor [ClfA]) were expressed in Staphylococcus carnosus and Lactococcus lactis subsp. cremoris. Both noninvasive gram-positive microorganisms are genetically distinct from S. aureus, lack any known S. aureus surface protein, and do not bind fibronectin. Transformants of S. carnosus and L. lactis harboring plasmids coding for various S. aureus surface proteins (FnBPA, FnBPB, and ClfA) functionally expressed adhesins (as determined by bacterial clumping in plasma, specific latex agglutination, Western ligand blotting, and binding to immobilized and soluble fibronectin). FnBPA or FnBPB but not of ClfA conferred invasiveness to S. carnosus and L. lactis. Invasion of 293 cells by transformants was comparable to that of strongly invasive S. aureus strain Cowan 1. Binding of soluble and immobilized fibronectin paralleled invasiveness, demonstrating that the amount of accessible surface FnBPs is rate limiting. Thus, S. aureus FnBPs confer invasiveness to noninvasive, apathogenic gram-positive cocci. Furthermore, FnBP-coated polystyrene beads were internalized by 293 cells, demonstrating that FnBPs are sufficient for invasion of host cells without the need for (S. aureus-specific) coreceptors.

Adhesins, Bacterial↗
PubMed1999

Ca2+ regulation of interactions between endoplasmic reticulum chaperones.

Casade Blue (CB), a fluorescent dye, was used to investigate the dynamics of interactions between endoplasmic reticulum (ER) lumenal chaperones including calreticulin, protein disulfide isomerase (PDI), and ERp57. PDI and ERp57 were labeled with CB, and subsequently, we show that the fluorescence intensity of the CB-conjugated proteins changes upon exposure to microenvironments of a different polarity. CD analysis of the purified proteins revealed that changes in the fluorescence intensity of CB-ERp57 and CB-PDI correspond to conformational changes in the proteins. Using this technique we demonstrate that PDI interacts with calreticulin at low Ca2+ concentration (below 100 microM), whereas the protein complex dissociates at >400 microM Ca2+. These are the Ca2+ concentrations reminiscent of Ca2+ levels found in empty or full ER Ca2+ stores. The N-domain of calreticulin interacts with PDI, but Ca2+ binding to the C-domain of the protein is responsible for Ca2+ sensitivity of the interaction. ERp57 also interacts with calreticulin through the N-domain of the protein. Initial interaction between these proteins is Ca2+-independent, but it is modulated by Ca2+ binding to the C-domain of calreticulin. We conclude that changes in ER lumenal Ca2+ concentration may be responsible for the regulation of protein-protein interactions. Calreticulin may play a role of Ca2+ "sensor" for ER chaperones via regulation of Ca2+-dependent formation and maintenance of structural and functional complexes between different proteins involved in a variety of steps during protein synthesis, folding, and post-translational modification.

Animals↗
PubMed1999

Inhibition by heparin and derivatized dextrans of Staphylococcus epidermidis adhesion to in vitro fibronectin-coated or explanted polymer surfaces.

The ability of Staphylococcus aureus to recognize several extracellular matrix or plasma proteins (e.g., fibrinogen, fibronectin, and collagen) promotes bacterial attachment to artificial surfaces. Whereas most S. aureus clinical isolates elaborate a wide repertoire of bacterial surface receptors' called adhesins, exhibiting specific binding of individual host proteins, S. epidermidis is lacking most of such protein adhesins. To document the interactions between S. epidermidis and various surface-adsorbed proteins, we first compared promotion of bacterial attachment by seven purified human proteins immobilized onto poly(methyl methacrylate) (PMMA) coverslips. Only two of them, namely fibronectin and fibrinogen, exhibited adhesion-promoting activities. In the presence of native heparin or two functionalized dextrans (CMDBS for Carboxy Methyl, Benzylamide sulfonate/sulfate), a dose-dependent inhibition of S. epidermidis adhesion to fibronectin-coated, but not to fibrinogen-coated surfaces was observed. The inhibitory effects of each CMDBS were much stronger than that of native heparin. In contrast, a control highly negatively charged, dextran exclusively substituted with carboxy methyl groups exerted no inhibition on S. epidermidis adhesion. To evaluate how CMDBS could interfere with S. epidermidis attachment to coverslips coated in vivo with extracellular matrix components, we also tested PMMA surfaces retrieved from tissue cages subcutaneously implanted in guinea pigs. Each CMDBS, but not heparin, strongly inhibited S. epidermidis adhesion to explanted coverslips, even in the presence of tissue cage fluid. In conclusion, fibronectin plays an important role in promoting S. epidermidis attachment to implanted biomaterials. Furthermore, S. epidermidis adhesion to fibronectin-coated or implanted biomaterials can be efficiently blocked in vitro by CMDBS.

Animals↗
PubMed1998

Clumping factor B (ClfB), a new surface-located fibrinogen-binding adhesin of Staphylococcus aureus.

The surface-located fibrinogen-binding protein (clumping factor; ClfA) of Staphylococcus aureus has an unusual dipeptide repeat linking the ligand binding domain to the wall-anchored region. Southern blotting experiments revealed several other loci in the S. aureus Newman genome that hybridized to a probe comprising DNA encoding the dipeptide repeat. One of these loci is analysed here. It also encodes a fibrinogen-binding protein, which we have called ClfB. The overall organization of ClfB is very similar to that of ClfA, and the proteins have considerable sequence identity in the signal sequence and wall attachment domains. However, the A regions are only 26% identical. Recombinant biotinylated ClfB protein bound to fibrinogen in Western ligand blots. ClfB reacted with the alpha- and beta-chains of fibrinogen in the ligand blots in contrast to ClfA, which binds exclusively to the gamma-chain. Analysis of proteins released from the cell wall of S. aureus Newman by Western immunoblotting using antibody raised against the recombinant A region of ClfB identified a 124 kDa protein as the clfB gene product. This protein was detectable only on cells that were grown to the early exponential phase. It was absent from cells from late exponential phase or stationary phase cultures. Using a clfB mutant isolated by allelic replacement alone and in combination with a clfA mutation, the ClfB protein was shown to promote (i) clumping of exponential-phase cells in a solution of fibrinogen, (ii) adherence of exponential-phase bacteria to immobilized fibrinogen in vitro, and (iii) bacterial adherence to ex vivo human haemodialysis tubing, suggesting that it could contribute to the pathogenicity of biomaterial-related infections. However, in wild-type exponential-phase S. aureus Newman cultures, ClfB activity was masked by the ClfA protein, and it did not contribute at all to interactions of cells from stationary-phase cultures with fibrinogen. ClfB-dependent bacterial adherence to immobilized fibrinogen was inhibited by millimolar concentrations of Ca2+ and Mn2+, which indicates that, like ClfA, ligand binding by ClfB is regulated by a low-affinity inhibitory cation binding site.

Adhesins, Bacterial↗
PubMed1998

Introduction of the mec element (methicillin resistance) into Staphylococcus aureus alters in vitro functional activities of fibrinogen and fibronectin adhesins.

Some methicillin-resistant strains of Staphylococcus aureus are defective in the production of major surface components such as protein A, clumping factor, or other important adhesins to extracellular matrix components which may play a role in bacterial colonization and infection. To evaluate the impact of methicillin resistance (mec) determinants on bacterial adhesion mediated by fibrinogen or fibronectin adhesins, we compared the in vitro attachment of two genetically distinct susceptible strains (NCTC8325 and Newman) to protein-coated surfaces with that of isogenic methicillin-resistant derivatives. All strains containing an intact mec element in their chromosomes were found to be defective in adhesion to fibrinogen and fibronectin immobilized on polymethylmethacrylate coverslips, regardless of the presence or absence of additional mutations in the femA, femB, or femC gene, known to decrease expression of methicillin resistance in S. aureus. Western ligand affinity blotting or immunoblotting of cell wall-associated adhesins revealed similar contents of fibrinogen- or fibronectin-binding proteins in methicillin-resistant strains compared to those of their methicillin-susceptible counterparts. In contrast to methicillin-resistant strains carrying a mec element in their genomes, methicillin-resistant strains constructed in vitro, by introducing the mecA gene on a plasmid, retained their adhesion phenotypes. In conclusion, the chromosomal insertion of the mec element into genetically defined strains of S. aureus impairs the in vitro functional activities of fibrinogen or fibronectin adhesins without altering their production. This effect is unrelated to the activity of the mecA gene.

Adhesins, Bacterial↗
PubMed1997

The dipeptide repeat region of the fibrinogen-binding protein (clumping factor) is required for functional expression of the fibrinogen-binding domain on the Staphylococcus aureus cell surface.

Clumping factor of Staphylococcus aureus is a fibrinogen-binding protein that is located on the bacterial cell surface. The protein has an unusual repeat domain (region R) comprising mainly the dipeptide aspartate and serine. To determine if region R has a role in the surface display of the fibrinogen-binding region A domain, deletions lacking the region R encoding region of the clfA gene were generated. To determine the minimum length of region R required for wild-type levels of ClfA expression, variants with truncated region R domains were constructed. S. aureus cells expressing mutated clfA genes were tested for (i) proteins released by lysostaphin treatment that reacted with antisera specific for region A, (ii) clumping in soluble fibrinogen, (iii) adherence to immobilized fibrinogen and (iv) expression of the ClfA antigen on the cell surface by fluorescent activated cell sorting analysis. Each construct expressed three major immunoreactive proteins, two of which were putative N-terminal degradation products. Region R residues greater than 40 were required between region A and W (72 residues between region A and the LPDTG sorting signal) for wild-type levels of clumping in fibrinogen. A stepwise decrease in clumping titre was observed as the distance between region A and LPDTG was decreased from 72 to 4 residues. Similarly, a decrease in binding of anti-ClfA serum and in binding to fibrinogen-coated plastic surfaces was observed with cells expressing ClfA with 40 region R residues or less. Nevertheless, low levels of adherence to fibrinogen and binding to anti-ClfA serum occurred with ClfA derivatives that lacked region R altogether. This indicates that a small proportion of the ClfA molecules are linked to peptidoglycan very close to the cell surface but that residues greater than 72 are needed to allow sufficient ClfA molecules to span the entire cell wall and to display the biologically active A domain in a form that can participate fully in fibrinogen binding.

Binding Sites↗
PubMed1997

Validation of reconstructed bremsstrahlung spectra between 6 MV and 25 MV from measured transmission data.

We have previously investigated a method of high-energy x-ray spectral reconstruction from transmission data by direct resolution of a matrix system. This technique uses the spectral vectorial algebra formalism. The resolution has previously been tested on a 12 MV photon beam. To extend and to test the validity of the results to the entire radiotherapy energy range, we have performed the method on photon beams with nominal energies of 6, 12, 15, and 25 MV. The influence on the 6 MV spectrum of a 60 degrees built-in wedge has also been investigated to test the sensitivity of the method and the results are reported. To validate our reconstructed spectra, dosimetric quantities such as tissue phantom ratios (TPR), water-to-air stopping power ratios (S/p) air water, and quality indexes TPR 10 (20) have been calculated. The results show good agreement between the measured and calculated data. Mean mass energy absorption coefficient ratios for different materials have also been computed and compared to data published recently and the results are very close (within +/- 0.5%). Primary depth dose functions in water have also been computed to deduce primary dose attenuation coefficients.

Evaluation Studies as Topic↗
PubMed1996

Physical and biological effects of a surface coating procedure on polyurethane catheters.

Central venous catheters are widely used in clinical practice; however, complications such as venous thrombosis or infection are frequent. The physical and biological effects of a coating procedure designed to improve the blood-contacting properties of polyurethane central venous catheters (CVCs) were studied. The surface atomic composition of poly(vinyl pyrrolidone) (PVP)-coated or uncoated Pellethane single lumen CVCs was characterized by electron spectroscopy for chemical analysis (ESCA), which confirmed the presence of an oxygen-rich PVP layer on the former material. Topological analysis of both single and triple lumen CVCs by scanning force microscopy (SFM) revealed a very smooth surface in PVP-coated catheters compared to the more frequent surface irregularities found either in uncoated Pellethane or in four additional randomly selected, commercially available triple lumen polyurethane CVCs. The PVP-coated Pellethane showed a strong reduction in either fibrinogen or fibronectin adsorption compared to all other PVP-free polyurethane CVCs. This decreased protein adsorption led to a proportional reduction in protein-mediated adhesion of either Staphylococcus aureus or Staphylococcus epidermidis and in the binding of a monoclonal antibody directed against the cell-binding domain of fibronectin. Increased surface smoothness and hydrophilic properties of polyurethane CVCs might decrease the risk of bacterial colonization and infection.

Adsorption↗
PubMed1996

A low-fibronectin-binding mutant of Staphylococcus aureus 879R4S has Tn918 inserted into its single fnb gene.

A low-fibronectin-binding mutant of Staphylococcus aureus strain 879R4SSp generated by transposon Tn918 mutagenesis is attenuated in a rat endocarditis model (J.M. Kuypers & R.A. Procter, 1989, Infect Immun 57, 2306-2312). PCR and Southern hybridization analysis with primers and probes, respectively, for the fnbA and fnbB genes of strains 8325-4 showed that strain 879R4SSp possesses a single fnb gene which is homologous to fnbA. This was confirmed by sequencing 41 bp of 5' non-coding and 237 bp of 5' coding DNA, which showed 97% base identity to fnbA. Southern hybridization and sequencing showed that Tn918 was inserted 41 bp 5' to fnbA in the mutant 879R4SSp/1536, between the promoter and initiation codon. Reduced adherence of the mutant to surface-bound fibronectin correlated with lower expression of a 180 kDa wall-associated fibronectin-binding protein.

Adhesins, Bacterial↗
PubMed1995

Indications for digital fluorography and storage-phosphor plates in pediatrics: certainties and questionable points.

We have used two digital imaging systems: digital fluorography and the phosphor plates system. The respective indications for each technique in pediatric practice are presented hereafter. Digital fluorography is highly recommended by dynamic examinations, and phosphor plates are highly recommended for conventional studies, if the spatial resolution is mandatory. Either digital fluorography or phosphor plates can be used for contrast studies. In pediatric radiology, if the spatial resolution is not mandatory, digital fluorography is suggested to reduce the radiation dose, and if using a small fields of view is possible, digital fluorography may be carefully discussed. Digital radiography is supported neither to be better than classical radiology nor to compensate for technician's mistakes. It is aimed to improve the department's functioning and, above all, to accommodate future innovations. Images can be transferred or archived through networks. This is a main prospect in the coming years.

Child↗
PubMed1995

Adhesion properties of mutants of Staphylococcus aureus defective in fibronectin-binding proteins and studies on the expression of fnb genes.

Staphylococcus aureus 8325-4 has the potential to express two distinct cell wall-associated fibronectin-binding proteins called FnBPA and FnBPB. In order to test if both proteins are expressed in S. aureus and if both are required for promoting bacterial adhesion to fibronectin-coated surfaces, insertion mutations were isolated in each gene. A DNA fragment encoding tetracycline resistance was inserted into fnbA and a fragment encoding erythromycin resistance was inserted into fnbB. A double fnbAfnbB mutant was also constructed. The fnbA and fnbB single mutants showed no significant reduction in their adhesion to polymethylmethacrylate coverslips that had been coated in vitro with fibronectin. However, the double mutant was completely defective in adhesion. Monospecific antibodies directed against the non-conserved N-terminal regions of both proteins confirmed the lack of expression of FnBPs in the mutant strains. Wild-type fnbA and fnbB genes cloned seperately on a multicopy plasmid were each able to restore fully the adhesion-defective phenotype of the 8325-4 fnbAfnbB mutant. This demonstrates that both fnb genes are expressed in S. aureus and that both contribute to the ability of strain 8325-4 to adhere to fibronectin-coated surfaces. The double mutant was also defective in adhesion to coverslips that had been removed from tissue cages implanted subcutaneously in guinea-pigs, which suggests that fibronectin is important in promoting attachment of S. aureus to biomaterial in vivo.

Adhesins, Bacterial↗