Spontaneous point mutations in the capsule synthesis locus leading to structural and functional changes of the capsule in serogroup A meningococcal populations

ABSTRACT

Whole genome sequencing analysis of 100 Neisseria meningitidis serogroup A isolates has revealed that the csaABCD-ctrABCD-ctrEF capsule polysaccharide synthesis locus represents a spontaneous point mutation hotspot. Structural and functional properties of the capsule of 11 carriage and two disease isolates with non-synonymous point mutations or stop codons in capsule synthesis genes were analyzed for their capsular polysaccharide expression, recognition by antibodies and sensitivity to bactericidal killing. Eight of eleven carriage isolates presenting capsule locus mutations expressed no or reduced amounts of capsule. One isolate with a stop codon in the O-acetyltransferase gene expressed non-O-acetylated polysaccharide, and was not recognized by anti-capsule antibodies. Capsule and O-acetylation deficient mutants were resistant to complement deposition and killing mediated by anti-capsular antibodies, but not by anti-lipopolysaccharide antibodies. Two capsule polymerase mutants, one carriage and one case isolate, showed capsule over-expression and increased resistance against bactericidal activity of both capsule- and lipopolysaccharide-specific antibodies. Meningococci have developed multiple strategies for changing capsule expression and structure, which is relevant both for colonization and virulence. Here we show that point mutations in the capsule synthesis genes substantially contribute to the repertoire of genetic mechanisms in natural populations leading to variability in capsule expression.

KEYWORDS:

• Neisseria meningitidis
• capsule synthesis locus
• genomic diversity
• herd immunity
• virulence

Abbreviations

BA	=	Bolgatanga District
DPBS-BSA	=	Dulbecco’s phosphate buffered saline – bovine serum albumin
CFU	=	colony-forming units
cps	=	capsule synthesis locus
ELISA	=	enzyme-linked immunosorbent assay
HPAEC-PAD	=	high-performance anion-exchange chromatography with pulsed amperometric detection
HR-MAS NMR	=	high-resolution magic angle spinning nuclear magnetic resonance
KND	=	Kassena-Nankana District
LPS	=	lipopolysaccharide
mAb	=	monoclonal antibody
MH	=	Mueller-Hinton
MLST	=	multilocus sequence typing
NHD	=	Nouna _Health District
SNPs	=	single-nucleotide polymorphism
ST	=	sequence type

Acknowledgments

We thank A. Bugri, A. Forgor, A. W. Hamid, A. Hodgson and S. Quaie (Navrongo Health Research Centre, Navrongo, Ghana), B. Coulibaly and A. Sie (Center de Recherche en Sante de Nouna, Nouna, Burkina Faso), J. P. Dangy, J. Hauser, J. Leimkugel, V. Pflüger and B. Rupinsky (Swiss Tropical and Public Health Institute, Basel, Switzerland), who were involved in establishing the original meningococcal isolate collections analyzed.

Disclosure statement

No potential conflict of interest was reported by the authors.

Trademark statement

Menveo is a trademark owned by or licensed to the GSK group of companies.

MenAfriVac is a trademark of Serum Institute of India Private Ltd.

Supplementary material

Supplemenatary data for this article can be accessed here.

Additional information

Funding

This work was supported by grant 310030_152840 of the Swiss National Science Foundation [Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. [310030_152840].