GENETIC MANIPULATION OF VIBRIO-CHOLERAE FOR VACCINE DEVELOPMENT - CONSTRUCTION OF LIVE ATTENUATED EL-TOR CANDIDATE VACCINE STRAINS

The recent spread of El Tor cholera to America augments the need for a n effective, safe and economical vaccine. In the present paper we desc ribe the construction of live attenuated V. cholerae strains by specif ically deleting the genes encoding cholera toxin and other putative to xins from the bacterial chromosome. To maximize the likelihood of expo sing protective antigens relevant to currently circulating vibrios we selected for genetic manipulation recent epidemic V. cholerae isolates from Peru. The mutant strains did not produce cholera toxin in vitro and in vivo. Deletion of the virulence cassette was accompanied by mar ked attenuation in the infant mouse cholera model. A selected El Tor O gawa candidate vaccine strain was refractory to acquisition of foreign genes by conjugation with toxigenic vibrios.