Construction And Characterization Of A Asd Gene Mutant Of A Strain Of The Attenuated Salmonella Typhimurium SL7207

Salmonella typhimurium is an intestinal and intracellular pathogen. Using invasive intracellular bacteria as a vectors to deliver gene vaccine is thought to offer considerable promise, because plasmid DNA can be directly presented to antigen presenting cells (APCs). Bacteria carrying DNA vaccine will be lysed within phagosome and released to cytosol and neucleus where these DNA vaccine will be expressed and induce both cellular and humoral immune response. The virulence of attenuated Salmonella is decreased while its ability to invade and replicate within host cells is not affected. SL7207 is one of the strains which is attenuated by deleting only one gene, aroA. Mutation of aroA makes SL7207 unable to synthesize arobic aminal acid. The attenuation was achieved because mammalial cells do not have arobic aminal acid leading to the limitation of its growth within the host cells.The attenuated strain SL7207 of Salmonella typhimurium is generally used as a vector to deliver DNA vaccine. Asd (aspartic semialdehyde dehydrogenase) gene encodes aspartic semialdehyde dehydrogenase, an enzyme involved in lysine, threonine, methionine and diaminopimelic acid (DAP) biosynthesis. DAP is an essential constituent of the cell wall of Gram-negative bacteria. Asd gene deletion mutant of Salmonella strains can not produce DAP leading to the lysis and death of bacteria. In this study, SL7207(asd-), the asd gene deletion mutant of the S. typhimurium strain (SL7207), was constructed by homologous recombination. The asd gene deletion mutant SL7207(asd-) was characterized by comparing its surviving and replicating both in vivo and in vitro with its parental strain SL7207.