Epidemiological and genetic charateristics of Vibrio vulnificus from diverse sources in China during 2012-2023

Abstract

Vibrio vulnificus is a significant zoonotic pathogen that causes severe vibriosis in humans and fish. The lack of a national annual surveillance program in China has hindered understanding of its epidemiological characteristics and genetic diversity. This study characterized 150 V. vulnificus isolates collected from diverse sources in China during 2012-2023, including seafood, aquaculture water, migratory birds, marine animals, and clinical patients. Most seafood-derived isolates and all 15 clinical isolates harbored the virulence-related gene vcgC and 16S rRNA type B. The isolates exhibited diverse virulence factors (VFs), including flagella, outer membrane components, RTX toxins, and multiple secretion systems. Genes associated with the Type III secretion system were identified in migratory bird isolates, while a unique Type VI secretion system (T6SS1) were identified exclusively within a specific phylogenetic sub-lineage. T6SS1-positive strains demonstrated an increased number of genomic islands (GIs) and VFs compared to T6SS1-negative strains. Enrichment of genes related to secretion systems and biofilm formation likely facilitated the expansion of the T6SS1-positive population. The novel association between T6SS1 and a specific sub-lineage underscores potential ecological and adaptive advantages. These findings provide new insights into the ecological and evolutionary dynamics of V. vulnificus.

Fig. 1. Global distribution of Vibrio vulnificus strains.

A The number of 150 newly collected V. vulnificus isolates in China over the past decade. B The percentage of isolates from various sources, categorized based on different molecular typing methods used in this study. C The number of V. vulnificus isolates reported by different countries over multiple years. D The geographical distribution of V. vulnificus sources worldwide. In (A) and (B), the term “environment” refers to aquaculture water samples.

Fig. 2. Phylogenetic analysis of Vibrio vulnificus strains using the maximum likelihood (ML) method.

The phylogenetic tree was constructed based on core-genome single nucleotide polymorphisms (SNPs). Metadata is displayed in the neighboring tracks (1 to 4) surrounding the tree: Track 1 represents the geographical region, Track 2 indicates the collection year, Track 3 denotes the host organism, and Track 4 includes virulence-associated gene types and 16S rRNA type. The presence of VFs and ARGs is indicated by darker colors. Shared VFs common to all 180 strains are not shown in the figure. Strains with names beginning with CNVV were sequenced explicitly for this study.

Fig. 3. BLAST ring comparison of reference V. vulnificus chromosome and plasmid with homologous sequences from isolates recovered in this study.

A Chromosome I; B Chromosome II. C Plasmid (reference strain Vv180806: GCA_014107515.1).GIs are highlighted in red in the outermost circle.

Fig. 4. Evolutionary history and KEGG enrichment analysis of V.vulnificus strains carrying T6SS1.

A Maximum likelihood (ML) phylogenetic tree of 128 T6SS1-positive strains and 402 T6SS1-negative strains. Branches representing T6SS1-positive strains are highlighted in blue. Adjacent tracks display metadata, including host organism, collection year, and geographical region. B Comparison of GIs carried by V. vulnificus in T6SS1-positive (n = 128) and T6SS1-negative (n = 402) groups. C KEGG enrichment analysis of differentially representative genes conducted on 193 V. vulnificus strains in Lineage L2, with absolute gene counts displayed. A significance threshold of P < 0.05 was applied. D Global epidemic trends of T6SS1-positive strains over time.The heatmap in (A) illustrates the presence of GIs in strain CNVV120 across global V. vulnificus isolates.

Fig. 5. Linear comparison of the T6SS1 genetic context among different strains in the Vibrio genus.

A Genetic environment of T6SS in various Vibrio strains. B Genetic environment of Hcp protein within T6SS. Arrows indicate open reading frame locations and transcriptional orientation. Blue cross-links highlight regions of significant sequence similarity, with identities exceeding 64%.