The molecular characteristic of Neisseria meningtidis serogroup X strain emerging in Jiangsu province, China, 2022.

Invasive meningococcal disease (IMD) is always caused by Neisseria meningitidis, presents a significant clinical challenge with high mortality rates (up to 20%) and not only neurological sequelae, but also physical and psychological sequelae in survivors. While vaccination has effectively reduced the incidence of traditional serogroups like A and C in China, the emergence of serogroup replacement due to capsular switching-horizontal gene transfer of capsular genes-threatens ongoing public health efforts. This study reports firstly the identification of a ST-7 NmX strain (20220811) in Jiangsu Province, China, suspected to have arisen from an ST-7 NmA progenitor via capsular switching. Whole-genome comparison and phylogenetic analysis revealed a high degree of core genome similarity between the X strain and ST-7 serogroup A strains. However, a significant divergence was observed within the capsular gene cluster region spanning ctrC to rfbA (~ 10.6 kb), with recombination breakpoints identified near these genes. These findings strongly suggest the acquisition of NmX capsule through large fragment recombination. Meantime, virulence factor analysis indicated the absence of adhesion-related genes opa and pilC in the X strain, potentially reflecting a trade-off between reduced invasive capacity and enhanced immune evasion.