The pathogenic species Neisseria meningitidis and Neisseria gonorrhoeae cause dramatically different diseases despite strong relatedness at the genetic and biochemical levels. N. meningitidis can cross the blood-brain barrier to cause meningitis and has a propensity for toxic septicemia unlike N. gonorrhoeae. We previously used subtractive hybridization to identify DNA sequences which might encode functions specific to bacteremia and invasion of the meninges because they are specific to N. meningitidis and absent from N. gonorrhoeae. In this report we show that these sequences mark eight genetic islands that range in size from 1.8 to 40 kb and whose chromosomal location is constant. Five of these genetic islands were conserved within a representative set of strains and/or carried genes with homologies to known virulence factors in other species. These were deleted, and the mutants were tested for correlates of virulence in vitro and in vivo. This strategy identified one island, region 8, which is needed to induce bacteremia in an infant rat model of meningococcal infection. Region 8 encodes a putative siderophore receptor and a disulfide oxidoreductase. None of the deleted mutants was modified in its resistance to the bactericidal effect of serum. Neither were the mutant strains altered in their ability to interact with endothelial cells, suggesting that such interactions are not encoded by large genetic islands in N. meningitidis.Neisseria meningitidis colonizes the nasopharynx, from which it can seed the bloodstream before crossing the blood-brain barrier (BBB) to cause meningitis. In contrast, Neisseria gonorrhoeae colonizes and invades the epithelium of the genitourinary tract, where it can cause a localized inflammation; bacteremia, though frequent, is asymptomatic and dissemination is rare. Thus, both species are capable of crossing a cellular barrier at their port-of-entry but they differ in their abilities to subsequently disseminate in the blood. The ability to induce intense and prolonged bacteremia is one of the prerequisites for a bacterial pathogen to cross the BBB. In contrast, the details of specific interactions with the cellular components of the BBB remain unclear. Therefore, in order to understand the mechanisms that allow N. meningitidis to cross the BBB, it will be necessary to identify the genes that are involved in bloodstream dissemination and/or specific interaction with the cellular components of the BBB. Such genes might be present in both N. meningitidis and N. gonorrhoeae but differ subtly in sequence or regulation, or they might be present in only one of the two species.Results from in vitro models have shown that most of the mechanisms mediating cellular interactions are common to both N. meningitidis and N. gonorrhoeae. On the other hand, several determinants have been identified that are specific to N. meningitidis: the polysaccharide capsule (8), the enzyme rotamase (26), the RTX toxin-like Frp proteins (29, 30), and a glutathione peroxidase (20). Of these, the capsule locus is ...

SummaryA two-dimensional structural model was devised for the Opc outer membrane protein invasin which contains 10 transmembrane strands and five surfaceexposed loops. One continuous epitope recognized by three monoclonal antibodies was localized to the tip of loop 2 by synthetic peptides and site-directed mutagenesis while a second, discontinuous epitope recognized by a fourth antibody was localized to loops 4 and 5 by insertion mutagenesis. These monoclonal antibodies are bactericidal and inhibit adhesion and invasion. Most of the T-cell epitopes defined by Wiertz et al. (1996) were localized to the transmembrane strands. Oligonucleotides encoding a foreign epitope (ٌ) from Semliki Forest virus were inserted into Bgl II restriction sites created by site-directed mutagenesis. The ٌ epitopes inserted in all five predicted loops were recognized on the cell surface of live Escherichia coli bacteria by a monoclonal antibody and are exposed while ٌ epitopes in the N-terminus or three predicted turns were not. The results thus confirm important predictions of the model and define five permissive sites within surface-exposed loops which can be used to insert foreign epitopes.