Expression of enterotoxigenicEscherichia colicolonization factors inVibrio cholerae

As a first step towards a vaccine against diarrhoeal disease caused by enterotoxigenicEscherichia coli(ETEC), we have studied the expression of several ETEC antigens in the live attenuatedVibrio choleraevaccine strain CVD 103-HgR. Colonization factors (CF) CFA/I, CS3, and CS6 were expressed at the surface ofV. choleraeCVD 103-HgR. Both CFA/I and CS3 required the co-expression of a positive regulator for expression, while CS6 was expressed without regulation. Up-regulation of CF expression inV. choleraewas very efficient, so that high amounts of CFA/I and CS3 similar to those in wild-type ETEC were synthesized from chromosomally integrated CF and positive regulator loci. Increasing either the operon and/or the positive regulator gene dosage resulted in only a small increase in CFA/I and CS3 expression. In contrast, the level of expression of the non-regulated CS6 fimbriae appeared to be more dependent on gene dosage. While CF expression in wild-type ETEC is known to be tightly thermoregulated and medium dependent, it seems to be less stringent inV. cholerae. Finally, co-expression of two or three CFs in the same strain was efficient even under the control of one single regulator gene.