Exocellulr toxic factors prowced by vibrio vulnificus

Vibrio vulnificus is an opportunistic human pathogen causing septicemia or wound-infections characterized by the formation of edema, necrotic ulcer and cellulitis on the skin. This bacterium produces various exocellular toxic factors, among which, 45 kDa protease and 56 (or 50) kDa cytolysin have been studied extensively. The protease is a zinc metalloprotease and degrades a number of biologically important proteins including elastin, fibrinogen, plasma protease inhibitors and complement components. It also enhances vascular permeability through activation of the Hag-factor-plasma kallikrein-kinin cascade and/or exmytotic histamine release from mast cells, and forms a hemorrhagic lesion which finally provokes severe dermonecrosis. Thus, the protease is the mast probable candidate for edema formation and bacterial invasion during the infection. Iron is an essential element for the growth of microorganisms. V. vulnificus is known to be able to utilize heme proteins such as hemoglobin as its sole iron source. Since V. vulnificus protease has the ability to digest heme proteins and to liberate heme residue fran globin protein, this enzyme may contribute to efficient heme uptake by the bacterium. However, V. vulnificus protease inoculated into a mmal is quickly inactivated by a 700 kDa plasma glycoprotein, alpha-macroglobulin, at molar ratio of 1 : 1. This plasma protein leaks fram the vascular system as a result of the permeability-enhancing and hemorrhagic actions of the protease, resulting in in situ inactivation of the protease by physical entrapment. It is therefore presumed that the depression of alpha-macroglobulin activity enhances the infectivity of V. vulnificus. V. vulnificus cytolysin can disrupt various eukaryotic cells, such as erythrocyte, mast cell and CHO (Chinese hamster ovary) cell, and an artificial vesicle, lipsome. Studies on its cytolytic action on the erythrocyte have shown that the cytotoxin initially binds to cell-surface cholesterol in a temperature independent mer. Then, some toxin molecules bound to the membrane aggregate and form a small (diameter of 53 nm) transmembrane-pore in a temperature dependent manner. Finally, the cell membrane is burst owing to the influx of extracellular substances including water via the pore resulting in the increase in the intracellular osmotic pressure. Some divalent cations (e.g. Ca2+ Mg²⁺ and Mn²⁺) block the final hemolytic stage by an unknown mechanism. This toxin also causes tissue damage and enhances permeability, perhaps due to histamine leakage from disrupted mast cells. Therefore, the cytolysin, like the protease, is also a putative factor for the development of skin lesions. Needless to say, the cytolysin seems to provide intracellularly stored-iron including hemoglobin to the bacterium. The gene encoding V, vulnificus cytolysin was cloned and sequenced, and this CNA fragment has been used as a probe for identification of the vibrio.