Attenuated strains of vibrio cholearae with improved biological safety features in freeze dried formfor oral vaccination

The present invention discloses new live attenuated strains for oral immunization against cholera that are provided in freeze dried formulations for long term storage and administration to humans. These strains combine the two most important properties of live attenuated cholera vaccine candidates. One such property is being well tolerated by people ingesting them. This was achieved by virtue of mutations already described in the art. The second property is having enhanced environmental safety due to the absence of VGJ¦ DNA in their genomes and also due to null mutations in the mshA gene or other spontaneous mutations conducive to the lack of MSHA type IV fimbria on the bacterial surface. This was done envisioning that VGJ¦ is a filamentous phage able to recombine with CTX¦ and disseminate the cholera toxin genes. This VGJ¦ phage as well as the VGJ¦-CTX¦ recombinants uses the MSHA fibers as receptor. Being devoid of MSHA fimbria the vaccine candidates are protected from acquiring CTX¦ from the recombinant hybrid VGJ¦-CTX¦. Being devoid of VGJ¦, the vaccine candidates are impaired in the dissemination of CTX¦, via VGJ¦.