NOVELTY – Constructing an attenuated mutant strain of pathogenic bacteria involves expressing Gam protein, Bet and Exo of bacteriophage lambda present in plasmid pKD46, and promoting the recombination of linear DNA fragments target. HU gene is provided for encoding the recombination cassette for gene enhancement, and for elimination of accessory gene present in the recombination cassette. USE – Method for constructing an attenuated mutant strain of pathogenic bacteria of family Enterobacteriaceae, Vibrionaceae, Francisellaceae and Legionellaceae and Salmonella spp., Shigella spp., Escherichia spp., Yersinia spp., Vibrio and Salmonella enterica serovar Typhimurium (ST662) for use in vaccine vector for stimulating humoral or cellular immune response against an infection caused by a pathogenic bacterium and salmonellosis (all claimed).