Research on pathogenic gienes and development of vaccine of Vibrio valunificus, a novel causative agent of foodborne infection

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Vibrio vulnificus is an important pathogens of foodborn diseases and wound infection. This pathogen causes fatal septicemia rapidly in immunocompromised hosts after they contact with contaminated seawater or seafood with this organism. The mortality rate is more than 50%. For the rapid progress and the high mortality,vaccination is considered an effective way to control infection with V. vulnificus in a high risk population. We applied Signature-Tagged Mutagenesis (STM) to generate attenuated mutants from a clinically-isolated virulent V. vulnificus strain, OPU1 which was isolated from a patient. Twelve insertion mutants were selected and the virulence of these mutants were determined by the minimal lethal dose (MLD) to mice. Several mutant strains showed lower virulence compare to the parent virulent strain. The DNA sequences flanking to transposon insertion sites in these mutants were determined and searched for homologies at DNA Date Bank of Japan. The transposons inserted genes were those for IMP dehydrogenase, UDP-N-acetylgulcosamin-2-epimerase, aspartokinase, and a conserved hypothetical protein. This suggests that these genes may be involved in V. vulnificusvirulence. One of the mutants was administrated for experimental vaccination to mice. The immunized mice were challenged with the virulent parent strain. All unimmunized mice were killed within 36 hr, but almost all immunized mice survived. In this experiment, we found that the attenuated have a potentiality as live vaccine candidate.