Suppression and inactivation ofVibrio vulnificushemolysin in cirrhotic ascites, a humanex vivoexperimental system

Regulation of the Vibrio vulnificus vvpE expression by cyclic AMP-receptor protein and quorum-sensing regulator SmcR

In Vibrio vulnificus, cAMP-receptor protein (CRP) and the quorum-sensing regulator SmcR are simultaneously and cooperatively required for the metalloprotease vvpE gene expression, rather than sequentially in a regulatory cascade. However, this study shows a new temporal and functional sequence between the two factors in regulating vvpE expression. A crp mutation inhibited vvpE expression with growth impairment from early stage. In contrast, a smcR mutation inhibited vvpE expression only at the late stage with no effect on growth. A crp-smcR double mutation severely inhibited vvpE expression with growth impairment from early stage. The inhibited vvpE expression was restored only at the early stage by a crp single complementation, but not at all by a smcR complementation. These results indicate that CRP functions as an essential activator, whereas SmcR functions in the presence of CRP for full vvpE expression.

Resveratrol modulates RTX toxin-induced cytotoxicity through interference in adhesion and toxin production

Host-parasite contact is a prerequisite for the acute cytotoxicity of Vibrio vulnificus, which is mediated primarily by RtxA1, a repeat in toxin (RTX) toxin. We found that resveratrol (at 10 or 30 microM), a natural polyphenol, protected HeLa cells from V. vulnificus cytotoxicity. To further characterize the underlying mechanism, the effect of resveratrol was investigated at the level of the host-microbe interactions. We studied the effects of resveratrol on adhesion, motility, cytotoxicity, and RtxA1 toxin expression of V. vulnificus. In addition, the effect of resveratrol on mouse mortality caused by V. vulnificus was investigated. Resveratrol inhibited V. vulnificus motility and the microbe adhesion to host cells, critical virulence traits for many bacteria. Resveratrol also down-regulated the expression of RtxA1 toxin at the transcriptional level and thereby protected the host cells from becoming rounded and damaged. In addition, resveratrol (20mg/kg) protected CD-1 mice from V. vulnificus infection. Taken together, these results suggest that resveratrol, a modulator of host-microbe interactions, has potential for development as a new paradigm drug to treat infectious diseases.

A widespread deferoxamine-mediated iron-uptake system in Vibrio vulnificus

Vibrio vulnificus can use the standard iron chelator deferoxamine (Desferal) for efficient iron-uptake via the specific receptor DesA, which is encoded by desA. We investigated the ubiquity of the deferoxamine-mediated iron-uptake system in V. vulnificus strains and the potential risk of the system. By polymerase chain reaction (PCR), desA was found in 10 of 10 clinical strains and in 9 of 10 environmental strains, and their growth was stimulated by deferoxamine. By reverse-transcriptase PCR, desA was expressed only under iron-limited conditions containing deferoxamine. V. vulnificus growth in the presence of deferoxamine was suppressed by desA mutation, and the suppressed growth was recovered by desA complementation. Deferoxamine stimulated V. vulnificus growth in iron-limited in vitro and ex vivo backgrounds containing transferrin-bound iron. Overall, V. vulnificus can use transferrin-bound iron via the widespread deferoxamine-mediated iron-uptake system; this cautions that deferoxamine therapy in patients with iron overload may increase the risk of fatal infections caused by V. vulnificus.