PubMed Health⌕ Search

Biomedical subjects

Henri Monteil

Publications and source records attributed to Henri Monteil.

At least 19 recordsLinked to original sources
PubMed2006

Engineered covalent leucotoxin heterodimers form functional pores: insights into S-F interactions.

The staphylococcal alpha-toxin and bipartite leucotoxins belong to a single family of pore-forming toxins that are rich in beta-strands, although the stoichiometry and electrophysiological characteristics of their pores are different. The different known structures show a common beta-sandwich domain that plays a key role in subunit-subunit interactions, which could be targeted to inhibit oligomerization of these toxins. We used several cysteine mutants of both HlgA (gamma-haemolysin A) and HlgB (gamma-haemolysin B) to challenge 20 heterodimers linked by disulphide bridges. A new strategy was developed in order to obtain a good yield for S-S bond formation and dimer stabilization. Functions of the pores formed by 14 purified dimers were investigated on model membranes, i.e. planar lipid bilayers and large unilamellar vesicles, and on target cells, i.e. rabbit and human red blood cells and polymorphonuclear neutrophils. We observed that dimers HlgA T28C-HlgB N156C and HlgA T21C-HlgB T157C form pores with similar characteristics as the wild-type toxin, thus suggesting that the mutated residues are facing one another, allowing pore formation. Our results also confirm the octameric stoichiometry of the leucotoxin pores, as well as the parity of the two monomers in the pore. Correctly assembled heterodimers thus constitute the minimal functional unit of leucotoxins. We propose amino acids involved in interactions at one of the two interfaces for an assembled leucotoxin.

Amino Acid Sequence↗
PubMed2006

Enhanced culture of Borrelia garinii and Borrelia afzelii strains on a solid BSK-based medium in anaerobic conditions.

The growth of 29 human strains from the three main pathogenic species of Borrelia burgdorferi sensu lato on a solid BSK-based medium was compared in two culture atmospheres: 3% CO(2) air and anaerobiosis. All strains grew under anaerobic conditions, whereas only 13 strains were able to grow in aerobiosis with 3% CO(2) (P<0.001). In the latter condition, 75% of the B. burgdorferi sensu stricto strains grew versus 33% of the B. garinii and B. afzelii strains. These data suggest that, especially for B. garinii and B. afzelii species, anaerobic conditions enhance growth yield and speed of low-passage Borrelia strains.

Anaerobiosis↗
PubMed2006

Homologous versus heterologous interactions in the bicomponent staphylococcal gamma-haemolysin pore.

Staphylococcal gamma-haemolysin HlgA-HlgB forms a beta-barrel transmembrane pore in cells and in model membranes. The pore is formed by the oligomerization of two different proteins and a still debated number of monomers. To clarify the topology of the pore, we have mutated single residues - placed near the right and left interfaces of each monomer into cysteine. The mutants were labelled with fluorescent probes, forming a donor-acceptor pair for FRET (fluorescence resonance energy transfer). Heterologous couples (labelled on complementary left and right interfaces) displayed a marked FRET, suggesting extensive HlgA-HlgB or HlgB-HlgA contacts. Heterologous control couples (with both components labelled on the same side) showed absent or low FRET. We found the same result for the homologous couple formed by HlgA [i.e. HlgA-HlgA in the presence of wt (wild-type) HlgB]. The homologous HlgB couple (HlgB-HlgB labelled on left and right interfaces and in the presence of wt HlgA) displayed a transient, declining FRET, which may indicate fast formation of an intermediate that is consumed during pore formation. We conclude that bicomponent pores are assembled by alternating heterologous monomers.

Amino Acid Substitution↗
PubMed2006

Mimicking helical antibacterial peptides with nonpeptidic folding oligomers.

Unnatural oligomeric scaffolds designed to adopt defined secondary structures (e.g., helices), while retaining the chemical diversity of amino acid side chains, are of practical value to elaborate functional mimetics of bioactive alpha-polypeptides. Enantiopure N,N'-linked oligoureas as short as seven residues long have been previously shown to fold into a stable helical structure, stabilized by 12- and 14-membered H-bonded rings. We now report that eight-residue oligoureas designed to mimic globally amphiphilic alpha-helical host-defense peptides are effective against both gram-negative and gram-positive bacteria (including methicillin-resistant Staphylococcus aureus [MRSA]) and exhibit selectivity for bacterial versus mammalian cells. Circular dichroism (CD) spectroscopy studies suggest enhanced helical propensity of oligoureas in the presence of phospholipid vesicles. The utility of this new class of nonpeptidic foldamers for biological applications is highlighted by high resistance to proteolytic degradation.

Amino Acid Sequence↗
PubMed2006

Incidence and pathogenic effect of Streptococcus pseudopneumoniae.

We evaluated the incidence of Streptococcus pseudopneumoniae in clinical isolates by phenotypic methods and DNA-DNA hybridization. The pathogenic role of this organism was investigated with the mouse peritonitis/sepsis model. Our results show a low incidence (1/120 pneumococcal isolates) and a potential pathogenic effect for S. pseudopneumoniae.

Animals↗
PubMed2005

Sensitive and specific detection of staphylococcal epidermolysins A and B in broth cultures by flow cytometry-assisted multiplex immunoassay.

Two of the most common bacterial skin infections of young infants and children are bullous impetigo due to Staphylococcus aureus and its more acute form, staphylococcal scalded skin syndrome. Epidermolysin A (ETA), ETB and, possibly, ETD are responsible for these diseases, which may appear as epidemics in pediatric patients. We tested the reliability of a flow cytometry-assisted multiplex immunoassay (Bio-Plex system) for the detection of ETA and ETB. The Bio-Plex system was found to be highly specific and highly sensitive for toxin concentrations of between 2 and 80,000 pg/ml. The results of this assay were 100% identical to the results of a PCR-based method. We demonstrated that this test did not generate any cross-reactions with ETD-producing isolates. The level of detection of ETB by this test differed according to culture conditions and from isolate to isolate; these results must be taken into account for diagnostic purposes.

Exfoliatins↗
PubMed2004

Crystal structure of leucotoxin S component: new insight into the Staphylococcal beta-barrel pore-forming toxins.

Staphylococcal leucocidins and gamma-hemolysins (leucotoxins) are bi-component toxins that form lytic transmembrane pores. Their cytotoxic activities require the synergistic association of a class S component and a class F component, produced as water-soluble monomers that form hetero-oligomeric membrane-associated complexes. Strains that produce the Panton-Valentine leucocidin are clinically associated with cutaneous lesions and community-acquired pneumonia. In a previous study, we determined the crystal structure of the F monomer from the Panton-Valentine leucocidin. To derive information on the second component of the leucotoxins, the x-ray structure of the S protein from the Panton-Valentine leucocidin was solved to 2.0 angstrom resolution using a tetragonal crystal form that contains eight molecules in the asymmetric unit. The structure demonstrates the different conformation of the domain involved in membrane contacts and illustrates sequence and tertiary structure variabilities of the pore-forming leucotoxins. Mutagenesis studies at a key surface residue (Thr-28) further support the important role played by these microheterogeneities for the assembly of the bipartite leucotoxins.

Amino Acid Sequence↗
PubMed2004

Determination of fosmidomycin in human serum and urine by capillary electrophoresis.

A capillary electrophoresis method with direct UV detection was developed for the determination of fosmidomycin, a promising new anti-malarial drug, in human serum and urine. Optimization of the separation parameters resulted in a buffer system adjusted to pH 10.8 containing a cationic reagent and an organic modifier. Under these conditions, the migration time of fosmidomycin was 5.2 min with serum and 7.4 min with urine samples. Validation of the method revealed good recoveries, precision and accuracy. The limit of quantification was 0.5 microg/ml in serum and 10 microg/ml in urine. The determination of fosmidomycin in serum was linear over a range of 0.1-150 microg/ml. Short and long-term stability tests resulted in no significant loss of fosmidomycin. The described technique will provide a fast and accurate analytical method for future pharmacokinetic studies.

Electrophoresis, Capillary↗
PubMed2004

Regulation of virulence determinants in Staphylococcus aureus: complexity and applications.

The virulence of Staphylococcus aureus is essentially determined by cell wall associated proteins and secreted toxins that are regulated and expressed according to growth phases and/or growth conditions. Gene expression is regulated by specific and sensitive mechanisms, most of which act at the transcriptional level. Regulatory factors constitute numerous complex networks, driving specific interactions with target gene promoters. These factors are largely regulated by two-component regulatory systems, such as the agr, saeRS, srrAB, arlSR and lytRS systems. These systems are sensitive to environmental signals and consist of a sensor histidine kinase and a response regulator protein. DNA-binding proteins, such as SarA and the recently identified SarA homologues (SarR, Rot, SarS, SarT, SarU), also regulate virulence factor expression. These homologues might be intermediates in the regulatory networks. The multiple pathways generated by these factors allow the bacterium to adapt to environmental conditions rapidly and specifically, and to develop infection. Precise knowledge of these regulatory mechanisms and how they control virulence factor expression would open up new perspectives for antimicrobial chemotherapy using key inhibitors of these systems.

Amino Acid Sequence↗
PubMed2004

Aeromonas simiae sp. nov., isolated from monkey faeces.

Two Aeromonas strains, IBS S6874(T) and IBS S6652, were isolated from the faeces of two healthy monkeys (Macaca fascicularis) from Mauritius that were kept in quarantine in the Centre for Primatology, Strasbourg, France. Phylogenetic analysis based on 16S rRNA gene sequences showed that the two isolates formed an unknown genetic lineage within the genus Aeromonas. The two isolates had nearly identical sequences (0.1 % nucleotide substitution) that were related closely to those of recognized Aeromonas species (1.7-3.5 % nucleotide substitution). DNA-DNA hybridization showed that strains IBS S6874(T) and IBS S6652 had high DNA-DNA similarity (89 %) to each other and a low level of DNA-DNA similarity to closely related taxa (18 % relatedness to Aeromonas trota and 16 % relatedness to Aeromonas schubertii). Phenotypically, the two monkey isolates differed from most previously described mesophilic Aeromonas species by their lack of haemolysis on sheep-blood agar and inability to produce indole, gas from glucose or acid from mannitol. They differed from the most closely related species, A. schubertii, by their ability to produce acid from D-cellobiose and D-sucrose and by their pyrazinamidase activity. The name Aeromonas simiae sp. nov. is proposed for these isolates; strain IBS S6874(T) (=CIP 107798(T)=CCUG 47378(T)) is the type strain.

Aeromonas↗
PubMed2004

Correlation of wbiI genotype, serotype, and isolate source within species of the Burkholderia cepacia complex.

Gram-negative bacteria of the Burkholderia cepacia complex (Bcc) are opportunistic pathogens that can infect the lungs of cystic fibrosis (CF) patients and can be transmitted among these patients, causing epidemics in the CF community. Lipopolysaccharide (LPS) is an important virulence factor of many gram-negative bacteria, with the O antigen component of LPS being responsible for serotype specificity. The goal of this work was to develop a genetic method of determining the serotype of Bcc isolates based on the conserved gene wbiI. Homologues of wbiI are found in polysaccharide biosynthesis gene clusters in other bacteria. Primers to a conserved region of the Bcc wbiI gene were able to amplify by PCR a single product in 67 of 80 Bcc isolates tested. Sequencing and restriction enzyme digestion of this wbiI PCR product revealed sufficient DNA polymorphisms to distinguish and group various isolates. In five of nine instances, Bcc isolates of a single serotype had a single wbiI restriction fragment length polymorphism (RFLP) pattern, while isolates of the other four serotypes could have multiple wbiI RFLP types. Species determination of the Bcc isolates revealed no obvious correlation between wbiI RFLP type and species. There was also no apparent correlation between wbiI RFLP type and the ability of a single Bcc isolate to infect an individual with CF. However three of five Bcc outbreaks involved isolates with the same wbiI RFLP type, indicating that wbiI RFLP typing may be a useful tool to help track Bcc outbreaks.

Base Sequence↗
PubMed2003

Staphylococcal epidermolysins.

PURPOSE OF REVIEW: Staphylococcal epidermolysins are the major causative toxins of bullous impetigo and staphylococcal scalded skin syndrome. This disease is characterized by the splitting of the epidermis between two cell layers resulting in exfoliation. It predominantly affects newborn babies and exposes them to secondary infections. This leads to the risk of epidemics, especially in nurseries. With only an experimental model which consists of skin injections in newborn mice and the recent determination of three-dimensional structures, the essential function of these toxins remained controversial, split between that of specific proteases and that of superantigens. RECENT FINDINGS: Staphylococcal epidermolysins now constitute a family of toxins, with the recent characterizations of two new serotypes: ETC and ETD. They may be secreted by sensitive or methicillin-resistant strains. Four molecules were also identified in Staphylococcus hyicus responsible for exudative epidermitis in swine. While different observations suggested a proteolytic action to these toxins, the histological parallel made with pemphigus foliaceus greatly helped in the characterization of the targets for epidermolysins ETA, ETB, ETD: desmoglein-1, a desmosome-constitutive protein, and incidentally melanocyte-stimulating hormones, which accounts for the blisters observed clinically. SUMMARY: The growing complexity in staphylococcal toxins has to be taken into account both for their association with diseases and for diagnosis purposes. Even though cases of staphylococcal scalded skin syndrome in adults are rare, they raise further questions about the pathogenic features of the disease such as individual sensitivity and distribution of the toxins into the body.

Adult↗
PubMed2003

Moxifloxacin efficacy and vitreous penetration in a rabbit model of Staphylococcus aureus endophthalmitis and effect on gene expression of leucotoxins and virulence regulator factors.

Bacterial endophthalmitis is a serious complication of ocular surgery and of eye trauma; the leading causative organisms are Staphylococcus aureus strains. Tissue damage is due both to the host inflammatory response and to toxin synthesis by bacteria. Systemic treatment remains difficult because most antibiotics show poor ocular penetration. Moxifloxacin (MXF), a novel fluoroquinolone, was evaluated for its penetration into the vitreous of normal rabbit eyes and of eyes of rabbits infected for 24 h with methicillin-susceptible and methicillin-resistant S. aureus (MSSA and MRSA) following a single intravenous administration of 5 or 20 mg/kg. MXF penetration was rapid and efficient regardless of the dose, ranging from 28 to 52%. An inflammatory state of the vitreous significantly increased penetration after the 20-mg/kg dose, with penetration reaching 52%. Concentrations determined in the vitreous cavity following a 20-mg/kg administration showed a 3.5-fold decrease of the bacterial density within 5 h for MSSA (MIC, 0.125 micro g/ml) and a 1.6-fold decrease for MRSA (MIC, 4 micro g/ml) strains, respectively. By using a semiquantitative reverse transcription-PCR method, the expression of luk-PV and hlgCB, but not hlgA, encoding staphylococcal leukotoxins, was detected in the vitreous without MXF treatment. A slight decrease in the expression of leucotoxins and sarA, agr, and sigB virulence regulatory factors was observed 1 h following the administration of 5 mg of MXF per kg.

Animals↗
PubMed2003

Control of the oxidative burst of human neutrophils by staphylococcal leukotoxins.

The ability of staphylococcal two-component leukotoxins to induce an oxidative burst and/or to prime human polymorphonuclear cells (PMNs) was studied by using spectrofluorometry or flow cytometry. At sublytic concentrations, the HlgA-HlgB, HlgA-LukF-PV, LukS-PV-LukF-PV, and HlgC-LukF-PV combinations of leukotoxins, but not the LukS-PV-HlgB and HlgC-HlgB combinations, were able to induce H(2)O(2) production similar to the H(2)O(2) production induced by 1 micro M N-formyl-Met-Leu-Phe (fMLP). In addition, when added at sublytic concentrations, all of the leukotoxin combinations primed PMNs for H(2)O(2) production induced by fMLP. Leukotoxin activation was dependent on the presence of Ca(2+) and was inhibited by wortmannin, an inhibitor of phosphatidylinositol 3-kinase, but not by N-methyl-L-arginine, an inhibitor of NO generation, which eliminates the possibility that NO plays a role in the action of leukotoxins. At higher concentrations, all leukotoxins inhibited H(2)O(2) production by PMNs activated by fMLP, phorbol 12-myristate 13-acetate (PMA), or the leukotoxins themselves. This inhibition was not related to the pore formation induced by leukotoxins. Intracellular release of H(2)O(2) induced by fMLP and PMA was not primed by leukotoxins but was inhibited. It seems that leukotoxin inhibition of H(2)O(2) release is independent of pore formation but secondary to an intracellular event, as yet unknown, triggered by leukotoxins.

Calcium↗