Genetic basis of meningococcal capsular switching between serogroups A and B belonging to ST-7.

OBJECTIVES

Capsular switching from serogroup A to serogroups C or X has been documented, whereas it is rarely observed from serogroup A to serogroup B. This study aims to report and characterize a rare capsular switching event from serogroup A to serogroup B belonging to ST-7.

METHODS

Comparative genomic analyses were performed on ST-7 isolates across serogroups A, B, C, and X. Recombination analysis of the cps locus was conducted to determine the recombination boundaries. The fitness costs of capsular switching were assessed by comparing bacterial growth assay, adhesion and invasive capacities of capsular switching strains.

RESULTS

Phylogenetic and average nucleotide identity (ANI > 99.9%) analysis suggested that the serogroup A strain probably represents their common progenitor. Recombination analysis of the cps locus indicated that the upstream recombination breakpoints were at ctrE, rfbB, and galE, while ctrC served as the downstream recombination boundary. Pathogenicity analysis showed that four serogroup isolates exhibited different growth rates during the exponential phase. The serogroup A isolate exhibited significantly greater capacities of adhesion and invasion.

CONCLUSION

This study reveals the occurrence of capsular switching from serogroup A to serogroup B in N. meningitidis, which facilitates immune evasion yet incurs fitness cost.