An Exocellular Cytolysin Produced by Vibrio vulnificus CDC B3547, a Clinical Isolate in Biotype 2 (Serovar E)

Vibrio vulnificus biotype 2, a primary eel pathogen, is also an opportunistic pathogen for humans. The strains in this biotype secrete a cytolysin into the culture medium. The cytolysin from the strain CDC B3547 (ATCC 33817), which was originally isolated from a human leg wound, can disrupt various kinds of eukaryotic cells including erythrocytes and mast cells, and artificial vesicles, liposomes. The cytolysin is a 50 kDa single‐chain protein and is categorized into the pore‐forming toxins. After binding tightly to the cell‐membrane cholesterol in a temperature‐independent manner, the toxin molecules assemble each other in a temperature‐dependent manner, forming a small transmembrane pore. When incubated with a metalloprotease from the same species, the cytolysin is converted to the nicked toxin composed of some peptide chains, joined with disulfide bond(s). This nicked toxin is more hydrophilic while maintaining comparable cytolytic activity.