AUTHOR=Murciano Celia , Lee Chung-Te , Fernández-Bravo Ana , Hsieh Tsung-Han , Fouz Belén , Hor Lien-I , Amaro Carmen 

TITLE=MARTX Toxin in the Zoonotic Serovar of Vibrio vulnificus Triggers an Early Cytokine Storm in Mice

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2017.00332

DOI=10.3389/fcimb.2017.00332

ISSN=2235-2988

ABSTRACT=<p><italic>Vibrio vulnificus</italic> biotype 2-serovar E is a zoonotic clonal complex that can cause death by sepsis in humans and fish. Unlike other biotypes, Bt2 produces a unique type of MARTX<sub>Vv</sub> (Multifunctional-Autoprocessive-Repeats-in-Toxin; RtxA1<sub>3</sub>), which is encoded by a gene duplicated in the pVvBt2 plasmid and chromosome II. In this work, we analyzed the activity of this toxin and its role in human sepsis by performing <italic>in vitro, ex vivo</italic>, and <italic>in vivo</italic> assays. First, we demonstrated that the ACD domain, present exclusively in this toxin variant, effectively has an actin-cross-linking activity. Second, we determined that the whole toxin caused death of human endotheliocytes and monocytes by lysis and apoptosis, respectively. Finally, we tested the hypothesis that RtxA1<sub>3</sub> contributes to human death caused by this zoonotic serovar by triggering an early cytokine storm in blood. To this end, we used a Bt2-SerE strain (R99) together with its <italic>rtxA1</italic><sub><italic>3</italic></sub> deficient mutant, and a Bt1 strain (YJ016) producing RtxA1<sub>1</sub> (the most studied MARTX<sub>Vv</sub>) together with its <italic>rtxA1</italic><sub><italic>1</italic></sub> deficient mutant, as controls. Our results showed that RtxA1<sub>3</sub> was essential for virulence, as R99ΔΔ<italic>rtxA1</italic><sub><italic>3</italic></sub> was completely avirulent in our murine model of infection, and that R99, but not strain YJ016, induced an early, strong and dysregulated immune response involving the up-regulation of a high number of genes. This dysregulated immune response was directly linked to RtxA1<sub>3</sub>. Based on these results and those obtained <italic>ex vivo</italic> (human blood), we propose a model of infection for the zoonotic serovar of <italic>V. vulnificus</italic>, in which RtxA1<sub>3</sub> would act as a sepsis-inducing toxin.</p>