Rank: Species
Lineage: Bacteria;Proteobacteria;Betaproteobacteria;Neisseriales;Neisseriaceae;Neisseria;Neisseria meningitidis
Description: The second of two pathogenic Neisseria, this organism causes septicemia and is the leading cause of life-threatening meningitis (inflammation of the meninges, the membrane surrounding the brain and spinal cord) in children. This organism typically residies in the nasopharynx cavity but can invade the respiratory epthelial barrier, cross into the bloodstream and the blood brain barrier, and cause inflammation of the meninges. The antiphagocytic capsular polysaccharide (CPS) aids in virulence. There are 5 serogroups based on CPS typing (A, B, C, Y, and W135). Serogroup B results in sporadic outbreaks in Europe and North America, and there is no vaccine currently. The use of a vaccine is hindered by the fact that the serogroup B capsular polysaccharide vaccine recognizes a common human carbohydrate, and vaccines against the surface proteins suffer due to the antigenic variability of those proteins. Pathogenicity factors include the surface proteins (porins and opacity proteins), and the type IV pilus (which is also found in Neisseria gonorrhoeae). The CPS is different in Neisseria gonorrhoeae as compared to Neisseria meningitidis and the CPS from Neisseria gonorrhoeae is not antiphagocytic. The type IV pilin subunit exhibits antigenic diversity through a cassette mechanism. There are 8 silent copies of the pilin gene in the chromosome, and these are recombined to create sequence differences which result in antigenic differences. Many virulence genes, especially those that code for cell surface proteins, contain homopolymeric tracts, which are sequences of high mutability. Slippage of the DNA replication machinery at these tracts results in mutation and potentially in antigenic variation. This organism, like Neisseria gonorrhoeae, is naturally competent, and protein complexes at the cell surface recognize the uptake signal sequence in extracellular DNA, an 8mer that is found at high frequency in Neisseria chromosomal DNA.
Reference Material:
https://www.ncbi.nlm.nih.gov/genome/?term=Neisseria%20meningitidis
