Abstract
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. Strain NMB-CDC was shown to be more hydrophobic than strain MC58 using hydrophobicity interaction chromatography and microbial adhesion-to-solvents assays. In conclusion, 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 which influence steps in meningococcal pathogenesis.
Highlights
Neisseria meningitidis is a Gram-negative diplococcus which is asymptomatically carried in the nasopharynx by approximately 10% of the adult population but is the causative agent of epidemic septicaemia and meningitis which results in 5–20% case fatality rates [1]
N. meningitidis strain NMB-CDC is the prototype sequence types (STs)-8 strain belonging to ST-8 cc while strain MC58 is the prototype ST-32 strain belonging to ST-32 cc
We sequenced and annotated the genome of strain NMB-CDC and used orthologous group (OG) clustering (OrthoMCL) analysis to show that this isolate is highly related to G2136 from the ST-8 cc [6] and FAM18 prototype strain of ST-11 cc but was least conserved with ST-32 cc representative strain MC58 (Figure S1)
Summary
Neisseria meningitidis is a Gram-negative diplococcus which is asymptomatically carried in the nasopharynx by approximately 10% of the adult population but is the causative agent of epidemic septicaemia and meningitis which results in 5–20% case fatality rates [1]. Based on the sequence similarity of housekeeping genes, N. meningitidis can be arranged into thirty-seven lineages of closely related sequence types (STs) termed clonal complexes (cc) which account for 61% of all strains collected [4]. Some of these clonal complexes are more often associated with carriage than disease (.2:1), while other clonal complexes have been deemed to be hyperinvasive as these strains are more commonly associated with invasive disease than carriage (generally .5:1) [5]. Despite the existence of carriage and hyperinvasive clonal complexes, the only common virulence determinants for invasiveness of disease causing isolates is encapsulation [7] and the carriage of phages [8]
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