POTENTIAL FOR REACQUISITION OF CHOLERA ENTEROTOXIN GENES BY ATTENUATED VIBRIO-CHOLERAE VACCINE STRAIN CVD 103-HGR

The potential for reacquisition of ctxA genes by attenuated Vibrio cho lerae O1 vaccine strain CVD 103-HgR was examined by performing a serie s of mating experiments under a variety of in vivo and in vitro condit ions. We found no evidence that CVD 103-HgR could reacquire ctxA genes from wild-type V. cholerae O1 strains. However, if the donor V. chole rae O1 strains were genetically manipulated to add genes that allow ch romosomal gene transfer, then ctxA sequences could be acquired by CVD 103-HgR. The minimal excretion of CVD 103-HgR by vaccinees and the ref ractoriness to reacquisition of ctxA sequences suggest that this well- tolerated, highly immunogenic live oral cholera vaccine will have a mi nimal environmental impact.