Genomic and epidemiological analysis of Vibrio parahaemolyticus O10:K4, a newly emerging serotype in China.

Vibrio parahaemolyticus is a leading cause of seafood-associated bacterial gastroenteritis, which poses increasing public health challenges worldwide. Since its emergence in approximately 2020, VP O10:K4 has rapidly become the dominant cause of gastroenteritis in China. Serotyping classification against 76 clinical isolates from Shandong indicated that O10:K4 reached a detection rate of approximately 90% by 2023. We performed a genomic analysis of these isolates alongside publicly available genomes from China and other regions. Genomic characterization revealed that all O10:K4 strains belonged to the same sequence type, ST3, and most possessed a conserved virulence and ARG profile, while they were divided into five distinct cg-STs via core-genome MLST analysis with higher resolution, with cg-ST1163 being the most predominant, accounting for 70%. Moreover, through comparative analysis, two newly distinct geno-serotypes, O10v1:K4 and O10v2:K4, were characterized, and each correlated strongly with specific cg-STs and occupied separate phylogenetic clades, suggesting the presence of different evolutionary pathways. In addition, a subset of strains recovered from a single city of Zhejiang was found to completely lack O- and K-antigen gene clusters, which may lead to O- and K-antigen deficiency-a genotype and subsequent phenotype never reported previously. Furthermore, through phylogenetic and clustering analyses, we identified 15 potential outbreak clusters, indicating both local and interprovincial spread, with cg-ST1163/O10v1:K4 being the most widespread and transmissible. In summary, our findings illustrate the population structure, spread patterns, and genomic diversity of the emerging O10:K4 pandemic clone, providing key insights for food safety management, public health surveillance and risk assessment.