Q-241. Distribution of the viuB Gene among Clinical and Environmental Vibrio vulnificus Strains Does Not Predict Virulence

M. Evans, V. Vedam-Mai, P. Thiaville, P. Gulig, A. C. Wright;
Univ. of Florida, Gainesville, FL.

Other researchers have demonstrated that the genes encoding vulnibactin siderophore synthesis (venB) and the outer membrane siderophore receptor (vuuA) are required for virulence of Vibrio vulnificus in animal models. However, comparison of siderophore expression in virulent vs. avirulent isolates is not consistent in the literature. Another iron uptake-related gene, viuB, encodes a cytoplasmic protein that has been shown to be involved in removal of iron from the siderophore-iron complex in V. cholerae. Recent publications indicated the presence of viub in V. vulnificus correlated with clinical origin, and they suggested that the gene was a virulence marker for this species. Our prior results showed that all strains examined produced siderophores; therefore, we speculated that the correlation of the presence of viuB with clinical origin was a consequence of polymorphic DNA sequences that prevented PCR amplification of this gene in non-clinical strains. Initial comparison of viuB sequence showed that the gene was highly conserved (97-99% DNA identity) among clinical strains, but that DNA polymorphisms were present at PCR priming site. When the PCR was repeated using new PCR primers derived from conserved sites in this gene, our results demonstrate that all strains (n=39) contained the viuB gene sequence in their genome. These strains were from both clinical and environmental origin and included highly virulent and less virulent phenotypes. Thus, although viuB may be essential for virulence in iron uptake, its presence cannot be used as a marker to predict virulence of V. vulnificus strains. DNA sequence comparisons and gene expression studies of highly virulent vs. less virulent strains are being used to determine the role of the viuB gene polymorphisms in the virulence of V. vulnificus.