[Neisseria meningitidis: characterisation and epidemiology].

Neisseria meningitidis are Gram-negative cocci, whose reservoir is exclusively human. This bacterium has several virulence factors including capsule with antiphagocytic properties, lipopolysaccharide, iron uptake system, pili and an IgA1 protease. The strains can be typed by immunological or genotypic methods. Phenotypic determination defines the serogroup, serotype, subtype and immunotype. Molecular typing, a very discriminating method, allows the determination of clonal complexes. These two epidemiological approaches allow the characterization of N. meningitidis strains. Conversely to the other strains, invasive strains belong to a very limited number of clonal complexes (CC). The evolution of the genome of N. meningitidis is the consequence of horizontal transfer of DNA occurring by transformation or recombination and leading to capsular exchanges. The distribution of the different serogroups varies according to the different countries. In France, in 2010, the serogroups B, C, W135 and Y accounted respectively for 72%, 17%, 5% and 2% of cases of invasive infections. The recent emergence of serogroup X in Niger highlights the need for continuing epidemiological surveillance.