Direct cytotoxicity to host cells by the MARTX toxin underlies the hypervirulence of foodborne Vibrio vulnificus
Vibrio vulnificus causes severe necrotizing wound infections and life-threatening foodborne infections. While clinical isolates of V. vulnificus are well-established as human pathogens, the pathogenic mechanisms underlying the virulence of food-derived isolates, particularly in the case of wound infections, remain poorly understood. This study aimed to elucidate the pathogenic mechanisms of a highly virulent, seafood-derived V. vulnificus isolate. A molecular survey of 28 V. vulnificus isolates from Shenzhen identified four MARTX toxin types, with the D-type predominating (36%). We characterized a representative shrimp-derived isolate, Vv3, which carries a chromosomal D-type MARTX with an ACD-MCF-ABH-MCF effector architecture. Using a newly established mouse wound infection model, Vv3 induced 100% mortality within 12 hours, with high bacterial loads detected systemically. Pathological analysis revealed severe tissue damage at the infection site, marked by muscle necrosis, and significant distal organ damage. Strikingly, flow cytometry analysis of splenocytes showed a significant depletion of macrophages and lymphocytes, rather than a classic cytokine storm, which was supported by transcriptomic data. To dissect the molecular drivers underlying the pathogenicity of food-derived V. vulnificus, we generated isogenic toxin mutants. In vitro assays demonstrated that the MARTX toxin was the primary mediator of rapid cell death in both macrophages and epithelial cells. Deletion of the GD-rich repeat domain in the MARTX toxin (?rtxA-GD) significantly reduced cytotoxicity and allowed cells to maintain their morphology, while deletion of hemolysin (?vvhA) had a minor effect. Critically, In vivo mice wound infections indicated that MARTX-deficient mutants with or without deletion of vvhA is unable to cause mortality in mice. These results establish that the D-type MARTX toxin is the dominant virulence determinant in this foodborne isolate, driving mortality through a direct destruction of host cells. This study highlights the severe risk posed by foodborne V. vulnificus in wound exposures and informs that the GD-rich region serves as a potential target for intervention against V. vulnificus infection. Overall design: To further elucidate the host transcriptional responses, we conducted high-throughput RNA sequencing (RNA-seq) on total RNA extracted from the spleen and small intestine tissues from Vv3-infected mice.