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Xavier Nassif

Publications and source records attributed to Xavier Nassif.

30 records · Page 2Linked to original sources
PubMed2003

Production of the signalling molecule, autoinducer-2, by Neisseria meningitidis: lack of evidence for a concerted transcriptional response.

Neisseria meningitidis is a Gram-negative bacterium which is an important causative agent of septicaemia and meningitis. LuxS has been shown to be involved in the biosynthesis of a quorum sensing molecule, autoinducer-2 (AI-2), known to play a role in virulence in Escherichia coli, as well as other bacteria. Evidence that serogroup B of N. meningitidis produces AI-2, along with the observation that a luxS mutant of this strain had attenuated virulence in an infant rat model of bacteraemia, led to further investigation of the role of this quorum sensing molecule in N. meningitidis. In this study, it is demonstrated that AI-2 is not involved in regulating growth of meningococci, either in culture or in contact with epithelial cells. Furthermore, transcriptional profiling using DNA microarrays shows an absence of the concerted regulation seen in other bacteria. Taken together, these data suggest that in N. meningitidis, AI-2 may be a metabolic by-product and not a cell-to-cell signalling molecule.

Animals↗
PubMed2003

Large-scale analysis of the meningococcus genome by gene disruption: resistance to complement-mediated lysis.

The biologic role of a majority of the Neisseria meningitidis 2100 predicted coding regions is still to be assigned or experimentally confirmed. Determining the phenotypic effect of gene disruption being a fundamental approach to understanding gene function, we used high-density signature-tagged transposon mutagenesis, followed by a large-scale sequencing of the transposon insertion sites, to construct a genome-wide collection of mutants. The sequencing results for the first half of the 4548 mutants composing the library suggested that we have mutations in 80%-90% of N. meningitidis nonessential genes. This was confirmed by a whole-genome identification of the genes required for resistance to complement-mediated lysis, a key to meningococcal virulence. We show that all the genes we identified, including four previously uncharacterized, were important for the synthesis of the polysialic acid capsule or the lipooligosaccharide (LOS), suggesting that these are likely to be the only meningococcal attributes necessary for serum resistance. Our work provides a valuable and lasting resource that may lead to a global map of gene function in N. meningitidis.

Antigens, Bacterial↗
PubMed2003

The REP2 repeats of the genome of Neisseria meningitidis are associated with genes coordinately regulated during bacterial cell interaction.

Interaction with host cells is essential in meningococcal pathogenesis especially at the blood-brain barrier. This step is likely to involve a common regulatory pathway allowing coordinate regulation of genes necessary for the interaction with endothelial cells. The analysis of the genomic sequence of Neisseria meningitidis Z2491 revealed the presence of many repeats. One of these, designated REP2, contains a -24/-12 type promoter and a ribosome binding site 5 to 13 bp before an ATG. In addition most of these REP2 sequences are located immediately upstream of an ORF. Among these REP2-associated genes are pilC1 and crgA, described as being involved in steps essential for the interaction of N. meningitidis with host cells. Furthermore, the REP2 sequences located upstream of pilC1 and crgA correspond to the previously identified promoters known to be induced during the initial localized adhesion of N. meningitidis with human cells. This characteristic led us to hypothesize that at least some of the REP2-associated genes were upregulated under the same circumstances as pilC1 and crgA. Quantitative PCR in real time demonstrated that the expression of 14 out of 16 REP2-associated genes were upregulated during the initial localized adhesion of N. meningitidis. Taken together, these data suggest that these repeats control a set of genes necessary for the efficient interaction of this pathogen with host cells. Subsequent mutational analysis was performed to address the role of these genes during meningococcus-cell interaction.

Bacterial Adhesion↗
PubMed2002

Microvilli-like structures are associated with the internalization of virulent capsulated Neisseria meningitidis into vascular endothelial cells.

Bacterial pathogens are internalized into non-phagocytic cells either by a zipper mechanism involving a direct contact between a bacterial ligand and a cellular receptor or a trigger mechanism secondary to the formation of membrane ruffles. Here we show that internalization of capsulated Neisseria meningitidis within endothelial cells following type IV pilus-mediated adhesion is associated with the formation of cellular protrusions at the site of bacterial attachment. These protrusions, like microvilli, are highly enriched in ezrin and moesin, two members of the ERM (ezrin/radixin/moesin) family, whereas vinculin and paxillin are absent. ERM-binding transmembrane proteins, such as CD44, and cortical actin polymerization colocalized within these membrane protrusions. Expression of dominant-negative ezrin largely prevented cortical actin polymerization, thus confirming the role of this molecule in bacteria-induced cytoskeletal modifications. Moreover, using selective inhibitors and dominant-negative mutants of the Rho family GTPases, we show that bacteria-induced actin polymerization required the activation of both Rho and Cdc42 but not of Rac1. Whereas GTPase inhibition dramatically reduced actin polymerization at the site of bacterial attachment, ezrin recruitment was not affected, indicating that bacterial adhesion promotes ezrin recruitment independently of the activity of the Rho-GTPases. Furthermore, GTPase inhibition largely reduced N. meningitidis entry into endothelial cells without affecting adhesion. We thus propose that following pilus-mediated adhesion, capsulated N. meningitidis recruit ERM-binding transmembrane proteins, as well as ezrin and moesin, and that both Rho and Cdc42 are critical for the subsequent cytoskeletal modifications responsible for the formation of microvilli-like cellular protrusions and bacterial internalization.

Actins↗
PubMed2002

How do extracellular pathogens cross the blood-brain barrier?

Bacterial invasion of the meninges can occur as a consequence of bloodstream invasion by some bacterial pathogens. Bacteria enter the central nervous system following a direct interaction with the luminal side of the cerebral endothelium, which constitutes the blood-brain barrier. To breach the barriers protecting the brain, extracellular pathogens must cross a monolayer of tight junction-expressing endothelial or epithelial cells. The limited number of pathogens capable of crossing these tight barriers and invading the meninges suggests that they display very specific attributes. For Neisseria meningitidis, type IV pili have been identified as being essential for meningeal invasion and it is believed other, as-yet-unidentified factors are also involved.

Animals↗
PubMed2002

Genomics of Neisseria meningitidis.

An important feature of disease caused by Neisseria meningitidis is the propensity to invade the meninges. Much progress has been made in our understanding of how this pathogen circumvents the physical properties of this cellular barrier. This review will address the new possibilities offered by the recent availability of meningococcal genome sequences.

Bacterial Proteins↗
PubMed2002

Representational difference analysis between Afa/Dr diffusely adhering Escherichia coli and nonpathogenic E. coli K-12.

Diffusely adhering Escherichia coli strains harboring Afa/Dr adhesins (Afa/Dr DAEC) have been associated with diarrhea and urinary tract infections (UTIs). The present work is the first extensive molecular study of a Afa/Dr DAEC strain using the representational difference analysis technique. We have searched for DNA sequences present in strain C1845, recovered from a diarrheagenic child, but absent from a nonpathogenic K-12 strain. Strain C1845 harbors part of a pathogenicity island (PAI(CFT073)) and several iron transport systems found in other E. coli pathovars. We did not find genes encoding factors known to subvert host cell proteins, such as type III secretion system or effector proteins. Several C1845-specific sequences are homologous to putative virulence genes or show no homology with known sequences, and we have analyzed their distribution among Afa/Dr and non-Afa/Dr clinical isolates and among strains from the E. coli Reference Collection. Three C1845-specific sequences (MO30, S109, and S111) have a high prevalence (77 to 80%) among Afa/Dr strains and a low prevalence (12 to 23%) among non-Afa/Dr strains. In addition, our results indicate that strain IH11128, an Afa/Dr DAEC strain recovered from a patient with a UTI, is genetically closely related to strain C1845.

Adhesins, Bacterial↗
PubMed2002

A uropathogenicity island contributes to the pathogenicity of Escherichia coli strains that cause neonatal meningitis.

We report that the archetypal Escherichia coli strain C5 causing neonatal meningitis harbors a pathogenicity island (PAI) designated PAI I(C5) that is similar to the PAI II(J96) of uropathogenic E. coli J96 inserted in the leuX-tRNA gene. PAI-negative C5 mutants had a lower capacity than C5 to induce high-level bacteremia in a neonatal rat model. However, no change in their resistance to the bactericidal effect of serum and their capacity to cross the blood-brain barrier was observed.

Animals↗
PubMed2002

Comparative genomics identifies the genetic islands that distinguish Neisseria meningitidis, the agent of cerebrospinal meningitis, from other Neisseria species.

Neisseria meningitidis colonizes the nasopharynx and, unlike commensal Neisseria species, is capable of entering the bloodstream, crossing the blood-brain barrier, and invading the meninges. The other pathogenic Neisseria species, Neisseria gonorrhoeae, generally causes an infection which is localized to the genitourinary tract. In order to investigate the genetic basis of this difference in disease profiles, we used a strategy of genomic comparison. We used DNA arrays to compare the genome of N. meningitidis with those of N. gonorrhoeae and Neisseria lactamica, a commensal of the nasopharynx. We thus identified sequences conserved among a representative set of virulent strains which are either specific to N. meningitidis or shared with N. gonorrhoeae but absent from N. lactamica. Though these bacteria express dramatically different pathogenicities, these meningococcal sequences were limited and, in contrast to what has been found in other pathogenic bacterial species, they are not organized in large chromosomal islands.

Bacterial Proteins↗