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

## TL;DR

Two new subtypes of Vibrio parahaemolyticus, O10:K4α and O10:K4β, have been circulating in Shanghai since 2020 and are now the dominant strains.

## Contribution

Identification of two distinct genotypes of Vibrio parahaemolyticus serotype O10:K4 co-circulating in Shanghai with unique genetic features.

## Key findings

- O10:K4α and O10:K4β subtypes emerged in Shanghai in 2019 and 2020, respectively, and are now dominant.
- The subtypes differ in genetic islands and O antigen-determining regions, showing closer relations to other serotypes.
- O10:K4β has a broader prevalence than O10:K4α, indicating a potential shift in strain dominance.

## Abstract

In this study, we conducted serotyping, virulence gene detection and whole-genome sequencing on Vibrio parahaemolyticus 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:K4α and O10:K4β) 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:K4α subtype first appeared in the Shanghai area in 2019, while the O10:K4β subtype first appeared in 2020. However, the O10:K4β subtype has a broader range of prevalence than the O10:K4α subtype. Upon comparison, it was found that both the O10:K4α subtype and the O10:K4β 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 V. parahaemolyticus, which is closer to the non-epidemic strain O4:K4. The SNP phylogenetic tree analysis revealed that the O10:K4α subtype has a close genetic relationship with the O10:KUT serotype strains, while the O10:K4β 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 V. parahaemolyticus genomes. The emergence of these two novel serotypes of V. parahaemolyticus is still in constant flux, so enhancing surveillance for V. parahaemolyticus is crucial for the prevention and control of foodborne illnesses it may cause.