Attenuated live strain of Salmonella Enterica Serovar Choleraesuis as a vaccine and vaccinal vehicle for swine livestock. The present invention provides a novel live and attenuated vaccinal strain, incapable of producing the alternative sigma factor (RpoS) and which, functions as a vaccinal vehicle for heterologous antigens. The strain is constructed by means of phase deletion of the totality of the gene which codifies the alternative sigma factor, rpoS, by means of homologous recombination. The strain is avirulent, genetically stable, lacks antibiotic resistance markers and is easily differentiated from wild strains.