Vibrio parahaemolyticus O4:K8 forms a potential predominant clone in southern China as detected by whole-genome sequence analysis

Abstract

Vibrio parahaemolyticus has been the most common food-borne pathogen in southern China, especially the O3:K6 pandemic clone and its serovariants. Recently, the serotype O4:K8 became more and more prevalent in southern China, which was different from the O3:K6 pandemic clone. Thus, the aim of the present work was to elucidate the molecular characteristics of the O4:K8. Some O3:K6 pandemic clone and its serovariants isolated in the same period were selected for comparative analysis, which were still dominant clone locally. The whole genome sequencing (WGS) was applied to characterize 20 strains of V. parahaemolyticus isolated from food-borne diarrheal cases and belonging to the serotype O4:K8, O3:K6 and O1:KUT (untypable), prevalent serotypes in recent southern China. The results showed that all these isolates were positive for the thermostable direct hemolysin gene (tdh), while negative for the TDH-related hemolysin gene (trh). We compared the V. parahaemolyticus strains to those of 31 strains isolated overseas and were available from NCBI genome database. A WGS-SNPs phylogenetic analysis of all the genomes revealed that the strains formed an important genetic lineage, which was genetically distinct from the O3:K6, O1:KUT and other internationals strains. Comparative genome analysis also revealed that all the O4:K8 strains carried the entire T3SS-1 and VpaI-7 (T3SS-2) regions, the most important virulent elements of the O3:K6 pandemic clone. However, all the O4:K8 strains lacked the entire VpaI-1 and VpaI-4 regions and carried only few ORFs of the VpaI-5 and VpaI-6, which were considered to be unique among post-1995 strains belonging to the O3:K6 pandemic clone. Our data showed that the O4:K8 strains possessed the virulence factors similar to the O3:K6 pandemic clone, which may have enabled them to become prevalent in southern China. Our study also revealed that WGS-bases analysis may help improve understanding epidemiology of this bacterium in food-borne disease surveillance.

Keywords: Phylogenetic analysis; SNPs; Vibrio parahaemolyticus; Whole genome sequence.