Two different genotypes of Vibrio parahaemolyticus serotype O10:K4 have been co-circulating in Shanghai since 2020

In this study, we conducted serotyping, virulence gene detection and whole-genome sequencing on <i>Vibrio parahaemolyticus</i> strains collected from the Shanghai area between 2017 and 2021. A total of 369 genomic sequences of different serotypes were obtained, including 155 serotype O10:K4 strains. It was found that the O10:K4 serotype presents two subtypes (O10:K4_α and O10:K4_β) co-circulated. They were both pandemic strains. Since 2020, the serotype O10:K4 has become the new dominant serotype in the Shanghai area. Among them, the O10:K4_α subtype first appeared in the Shanghai area in 2019, while the O10:K4_β subtype first appeared in 2020. However, the O10:K4_β subtype has a broader range of prevalence than the O10:K4_α subtype. Upon comparison, it was found that both the O10:K4_α subtype and the O10:K4_β subtype carry different unique genetic islands, and the compositions of the O antigen-determining region are also different. The O antigen-determining region has low similarity with the O10 group of <i>V. parahaemolyticus</i>, which is closer to the non-epidemic strain O4:K4. The SNP phylogenetic tree analysis revealed that the O10:K4_α subtype has a close genetic relationship with the O10:KUT serotype strains, while the O10:K4_β subtype has a closer relationship with the O10:K60 serotype strains, which is consistent with the results of core genome multilocus sequence typing analysis using the public database of <i>V. parahaemolyticus</i> genomes. The emergence of these two novel serotypes of <i>V. parahaemolyticus</i> is still in constant flux, so enhancing surveillance for <i>V. parahaemolyticus</i> is crucial for the prevention and control of foodborne illnesses it may cause.