Search

International audience; A scientist in our laboratory was accidentally infected while working with Z5463, a Neisseria meningitidis serogroup A strain. She developed severe symptoms (fever, meningism, purpuric lesions) that fortunately evolved with antibiotic treatment to complete recovery. Pulse-field gel electrophoresis confirmed that the isolate obtained from the blood culture (Z5463BC) was identical to Z5463, more precisely to a fourth subculture of this strain used the week before the contamination (Z5463PI). In order to get some insights into genomic modifications that can occur in vivo, we sequenced these three isolates. All the strains contained a mutated mutS allele and therefore displayed an hypermutator phenotype, consistent with the high number of mutations (SNP, Single Nucleotide Polymorphism) detected in the three strains. By comparing the number of SNP in all three isolates and knowing the number of passages between Z5463 and Z5463PI, we concluded that around 25 bacterial divisions occurred in the human body. As expected, the in vivo passage is responsible for several modifications of phase variable genes. This genomic study has been completed by transcriptomic and phenotypic studies, showing that the blood strain used a different haemoglobin-linked iron receptor (HpuA/B) than the parental strains (HmbR). Different pilin variants were found after the in vivo passage, which expressed different properties of adhesion. Furthermore the deletion of one gene involved in LOS biosynthesis (lgtB) results in Z5463BC expressing a different LOS than the L9 immunotype of Z2491. The in vivo passage, despite the small numbers of divisions, permits the selection of numerous genomic modifications that may account for the high capacity of the strain to disseminate.

International audience; Cerebrospinal meningitis is a feared disease that can cause the death of a previously healthy individual within hours. Paradoxically, the causative agent, Neisseria meningitidis, is a common inhabitant of the human nasopharynx, and as such, may be considered a normal, commensal organism. Only in a small proportion of colonized people do the bacteria invade the bloodstream, from where they can cross the blood–brain barrier to cause meningitis. Furthermore, most meningococcal disease is caused by bacteria belonging to only a few of the phylogenetic groups among the large number that constitute the population structure of this genetically variable organism. However, the genetic basis for the differences in pathogenic potential remains elusive. By performing whole genome comparisons of a large collection of meningococcal isolates of defined pathogenic potential we brought to light a meningococcal prophage present in disease-causing bacteria. The phage, of the filamentous family, excises from the chromosome and is secreted from the bacteria via the type IV pilin secretin. Therefore, this element, by spreading among the population, may promote the development of new epidemic clones of N. meningitidis that are capable of breaking the normal commensal relationship with humans and causing invasive disease.

International audience; Many proteins, especially membrane and exported proteins, are stabilized by intramolecular disulfide bridges between cysteine residues without which they fail to attain their native functional conformation. The formation of these bonds is catalyzed in Gram-negative bacteria by enzymes of the Dsb system. Thus, the activity of DsbA has been shown to be necessary for many phenotypes dependent on exported proteins, including adhesion, invasion, and intracellular survival of various pathogens. The Dsb system in Neisseria meningitidis, the causative agent of cerebrospinal meningitis, has not, however, been studied. In a previous work where genes specific to N. meningitidis and not present in the other pathogenic Neisseria were isolated, a meningococcus-specific dsbA gene was brought to light (Tinsley, C. R., and Nassif, X. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 11109-11114). Inactivation of this gene, however, did not result in deficits in the phenotypes commonly associated with DsbA. A search of available genome data revealed that the meningococcus contains three dsbA genes encoding proteins with different predicted subcellular locations, i.e. a soluble periplasmic enzyme and two membrane-bound lipoproteins. Cell fractionation experiments confirmed the localization in the inner membrane of the latter two, which include the previously identified meningococcus-specific enzyme. Mutational analysis demonstrated that the deletion of any single enzyme was compensated by the action of the remaining two on bacterial growth, whereas the triple mutant was unable to grow at 37 °C. Remarkably, however, the combined absence of the two membrane-bound enzymes led to a phenotype of sensitivity to reducing agents and loss of functionality of the pili. Although in many species a single periplasmic DsbA is sufficient for the correct folding of various proteins, in the meningococcus a membrane-associated DsbA is required for a wild type DsbA؉ phenotype even in the presence of a functional periplasmic DsbA.

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.