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

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Abstract
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.