Virulence linked to polysaccharide production in serogroup BNeisseria meningitidis

Bacterial capsules, in general, are composed of polypeptides or polysaccharides and have been implicated in the virulence of a number of bacterial pathogens 1. Neisseria meningitidis does not elaborate a capsule which can be observed readily as a cellular organelle, however, the various serogroups do elaborate group-specific polysaccharide 2. This polysaccharide is a homopolymer of N-acetylneuraminic acid linked a (2 ~ 8), in the case of the serogroup B strains. Rough and smooth variants from a given strain have been observed and it has been suggested that the presence of polysaccharide on smooth variants could be associated with virulence 3. However, the biosynthetic pathways for polysaccharide production, their regulation, and the role that polysaccharide plays in virulence of N. meningitidis remain obscure. Spontaneous isogenic mutants of serogroup B N. meningitidis strain M986, which were deficient in polysaccharide production and release, were examined for their virulence for mice. The loss of polysaccharide biosynthetic capability in the mutants resulted in a dramatic loss in virulence for mice, which was regained upon reversion to the wild-type phenotype.