Hyperinvasive and quinolone-resistant meningococci cc4821 achieved immune evasion through capsule switching

Neisseria meningitidis stands as one of the predominant etiological agents of bacterial meningitis worldwide. Sequence type (ST) 4821 clonal complex (cc4821), notably linked to the hyperinvasive and quinolone-resistant clone China^{CC4821-R1-C/B}, has emerged and caused the epidemiological shift from serogroup A (MenA, mostly cc5 and cc1) to MenC in China since 2003 and the subsequent introduction of MenA + C vaccination. However, the evolution path of capsule in MenB China^{CC4821-R1-C/B} under the vaccine-induced selective pressure remains unclear. For phylogenetic analysis, nucleotide sequences of the capsular polysaccharide synthesis (cps) gene cluster were extracted from MenC and MenB China^{CC4821-R1-C/B} genomes in the Neisseria PubMLST Database. Recombination analyses were conducted using software MEGA and RDP. The capsule switching from MenC to MenB in China^{CC4821-R1-C/B} was conducted via natural transformation.

Phylogenetic analysis of the cps loci revealed that recombination events probably occurred in region A. Among MenB China^{CC4821-R1-C/B} isolates, isolate Nm119 (B: P1.7-2,14: F3-3: ST-9455 [cc4821]) was selected as the representative strain. Through sequence analysis, a potential donor strain (2061370; B: P1.19-1,15 - 11: F3-7: ST-269 [cc269]) was identified from 80 candidate isolates, with a 5,527-bp recombination sequence spanning the region between ctrG and cssA in region A. To further validate capsule switching from MenC to MenB, we performed biological experiments using a MenC China^{CC4821-R1-C/B} isolate (Nm044; C: P1.7-2,14: F3-3: ST-4821 [cc4821]) as a recipient strain. The recombination sequence identified in the transformant (Nm044Nm119_T20) was only 414 bp larger than the sequence predicted by the in silico analysis. Functional analysis of the transformant revealed that its capsular polysaccharide expression and serum survival capacity were comparable to those of the donor strain. The capsule switching pattern, exemplified by Nm119, could serve as a model for MenB China^{CC4821-R1-C/B}. Through MenC→MenB capsule switching, China^{CC4821-R1-C/B} isolates have gained the capacity to evade immunity induced by MenA + C vaccines.

The potential capsule switch from MenC→MenB in China^{CC4821-R1-C/B} isolates has been confirmed through both sequence-based analyses and molecular biological experiments. The MenB capsule likely originated from a cc269 strain. Given the potential of capsule switching events to compromise vaccine efficacy, enhanced surveillance of capsule variation in cc4821 isolates is warranted under current immunization strategies in China.