Genetic fusion of a non-toxic heat-stable enterotoxin-related decapeptide antigen to cholera toxin B-subunit.

A decapeptide highly homologous to the STa Escherichia coli heat-stable enterotoxin and to several other heat-stable enterotoxins was fused genetically to the amino-end of the B-subunit of cholera toxin (CTB) and the hybrid protein gene expressed from a tacP overexpression system. The STa-related decapeptide used, which was encoded by a synthetic oligodeoxynucleotide, contained a single mutation which substituted a disulfide-linked cysteine by alanine. After its fusion to CTB the decapeptide was able to both react with and to give rise to anti-STa antibodies. Expression of the decapeptide-CTB hybrid by non-toxigenic Vibrio cholerae resulted in its full secretion into the extracellular milieu from where it could then be readily purified by single-step affinity chromatography using immobilized GM1 ganglioside. Bacteria producing this non-toxic, immunogenic decapeptide-CTB toxoid might be useful for the development of oral vaccines against diarrhea caused by E. coli and other bacteria producing immunologically related heat-stable enterotoxins, and as a source of immunoreagents for methods used to diagnose disease caused by these bacteria.