Genomic Insight into Zoonotic and Environmental Vibrio vulnificus: Strains with T3SS2 as a Novel Threat to Public Health

<i>Vibrio vulnificus</i> is a significant opportunistic pathogen with the highest fatality rate among foodborne microbes. However, due to a lack of comprehensive surveillance, the characteristics of isolates in China remain poorly understood. This study analyzed 60 strains of <i>V. vulnificus</i> isolated from diverse sources in Shanghai, including shellfish, crabs, shrimps, throat swabs of migratory birds, as well as seafood farming water and seawater. Identification of the genotypes was performed using PCR, and cytotoxicity was determined using an LDH assay. DNA was sequenced using Illumina NovaSeq followed by a bioinformatic analysis. The results demonstrated that a majority of the strains belonged to the 16S rRNA B-<i>vcg</i>C genotype. All strains carried five antibiotic resistance genes (ARGs), with some strains carrying over ten ARGs, mediating resistance to multiple antibiotics. Five strains possessed a highly abundant effector delivery system, which further investigations revealed to be a type III secretion system II (T3SS2), marking the first description of T3SS2 in <i>V. vulnificus</i>. Phylogenetic analysis indicated that it belonged to a different genetic lineage from T3SS2α and T3SS2β of <i>V. parahaemolyticus</i>. Bacteria with T3SS2 sequences were concentrated in coastal areas and mostly within the genus <i>Vibrio</i> in the global prevalence survey. Our study provides essential baseline information for non-clinical <i>V. vulnificus</i> and discovers the existence of T3SS2 in several strains which may be more virulent, thereby posing a new threat to human health.