The role of surface glycans in the attachment and invasion of Neisseria meningitidis into host epithelial cells

[Truncated] The major surface carbohydrates of Neisseria meningitidis include the capsule, lipooligosaccharide and the pilin glycan. Each of these structures are regulated and are variably distributed between strains of the species. Although alterations to the surface carbohydrates of the meningococcus are thought to aid in evasion of the host immune response, they also modulate virulence. As such the aims of this study were to examine the capsule, pilin glycan and lipooligosaccharide structure and regulatory pathways in the attachment and invasion of host epithelial cells.
We compared exemplar strains from two hypervirulent clonal complexes, strain NMB-CDC from ST-8/11 cc and strain MC58 from ST-32/269 cc, in host cell attachment and invasion. Strain NMB-CDC attached to and invaded host cells at a significantly greater frequency than strain MC58. Type IV pili retained the primary role for initial attachment to host cells for both isolates regardless of pilin class and glycosylation pattern. In strain MC58, the serogroup B capsule was the major inhibitory determinant affecting both bacterial attachment to and invasion of host cells. Removal of terminal sialylation of lipooligosaccharide (LOS) in the presence of capsule did not influence rates of attachment or invasion for strain MC58. However, removal of either serogroup B capsule or LOS sialylation in strain NMB-CDC increased bacterial attachment to host cells to the same extent. Although the level of inhibition of attachment by capsule was different between these strains, the regulation of the capsule synthesis locus by the two-component response regulator MisR, and the level of surface capsule determined by flow cytometry were not significantly different. However, the diplococci of strain NMB-CDC were shown to have a 1.89-fold greater surface area than strain MC58 by flow cytometry. It was proposed that the increase in surface area without changing the amount of anchored glycolipid capsule in the outer membrane would result in a sparser capsule and increase surface hydrophobicity. Capsulation modulated the surface hydrophobicity of both isolates however encapsulated strain MC58 was more hydrophilic than strain NMB-CDC. In conclusion, strain MC58 adhered less to host cells and had a more hydrophilic surface than strain NMB-CDC. Improved levels of adherence of strain NMB-CDC to cell lines was associated with increased bacterial cell surface and surface hydrophobicity. This study shows that there is diversity in bacterial cell surface area and surface hydrophobicity within N. meningitidis and that this phenotype can influence steps in meningococcal pathogenesis.