Survival of Vibrio vulnificus genotypes in male and female serum, and production of siderophores in human serum and seawater.

Vibrio vulnificus is an estuarine bacterium responsible for 95% of all seafood-related deaths in the United States. Several studies have demonstrated that V. vulnificus infections are enhanced when host iron availability is increased, such as occurs with chronic liver disease. Because of the gender difference seen in these infections, we examined whether there was a difference in the survival in both male and female serum by both the C (clinical) and E (environmental) genotypes of V. vulnificus. We further determined the significance of the catecholate and hydroxamate siderophores produced by this pathogen during both human infections and while in its natural estuarine environment. We found that only C-genotype strains were capable of growth in human serum, regardless of inoculum size, with growth in male and female serum being equal. We found the catecholate outer membrane receptor gene (vuuA) to be expressed significantly more than that for the hydroxamate siderophore (fhuA) when the cells were exposed to human serum, regardless of the genotype. When cells were exposed to natural seawater, fhuA showed increased expression over time, while vuuA showed decreased expression. Our data suggest that the catecholate siderophore is important during human infections, whereas the hydroxamate siderophore may be more important in the estuarine environment this pathogen inhabits.