Abstract: The present invention relates to a recombinant Vibrio cholerae strain, a vaccine comprising said strain, the use of said strain, and methods for its production. The recombinant strain according to the invention is comprising DNA sequences coding for at least the ETEC pili CFA/1, CS3 and CS6, wherein the DNA sequences are operationally linked to one or more promoters. The strain of the invention may be used in a vaccine composition for immunization against ETEC and/or cholera. The present invention further relates to methods for enhancing the surface expression of ETEC pili in a V. cholerae strain.

Abstract: The present invention relates to live attenuated gram-negative vaccine carrier strains which are useful for expression and delivery of heterologous O-antigens (O-PS) from gram-negative pathogens. Said strains are deficient in the expression of homologous O-PS due to a defined genetic modification, preferably a deletion, and, thus, capable of efficiently expressing a desired heterologous O-PS in such a way that it is covalently coupled either to homologous or heterologous LPS core lipid A. The present invention furthermore relates to live vaccine carrier strains containing a heterologous gene or a set of heterologous genes encoding O-PS. Preferably, said strains additionally contain genes necessary for the synthesis of complete smooth heterologous LPS. The present invention also relates to live vaccines comprising said strains, preferably for immunization against gram-negative enteric pathogens.