What is the role of free iron in the pathophysiology of Vibrio infections?

Updated: Jun 21, 2021
  • Author: Hoi Ho, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

Several mechanisms contribute to the virulence of V vulnificus. Iron is an important growth factor. However, because free iron is virtually absent in humans, the organism produces siderophores that acquire iron from transferrin or lactoferrin and deliver it to the bacteria. Conversely, the inability to produce siderophores leads to reduction of virulence. Hepcidin, a natural cysteine-rich peptide, has recently been suggested to possess important antibacterial activity. It is possible that inadequate expression of hepcidin in patients with liver disease predisposes them to serious infections, including those caused by Vibrio species. [12, 13]

Clinical conditions associated with increased free iron, such as hemochromatosis or hemolytic anemia, represent a major risk factor for disseminated Vibrio infections. In addition, V vulnificus produces several other virulence factors, including proteases, hemolysins, and cytolysins. One in particular, a thermolysin-like metalloprotease, activates the bradykinin pathway, causing an increase in vascular permeability. This metalloprotease is far more efficient at activating human enzymes than those of other Vibrio species, possibly explaining why V vulnificus causes severe skin damage and necrotizing fasciitis. [14]

A study in mice, however, has shown that metalloprotease is not necessarily fundamental for the virulence of V vulnificus. The absence of protease activity resulted in increased cytolysin activity that may have contributed to the enhanced virulence. [15] On animal models, a protease-deficient mutant of V vulnificus was as virulent as the wild-type strain.


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