The role of the traT gene of the Salmonella typhimurium virulence plasmid for serum resistance and growth within liver macrophages.

The role of the traT gene of the Salmonella typhimurium virulence plasmid for the serum resistance of the bacteria and their growth within mouse liver macrophages was investigated. The gene product, the TraT protein, increased the serum resistance in E. coli HB101, which naturally does not carry traT. It also contributed to the serum tolerance of S. typhimurium. The capacity of an isogenic S. typhimurium TML strain triplet, differing in their ability to express TraT and in the quality of the traT gene expressed, to grow in vivo in the mouse liver indicated that, although TraT was dispensable for the net growth of the bacteria within the liver, the expression of a mutated traT gene reduced the growth rate. The traT gene was mapped on the virulence plasmid outside previously defined virulence determinants suggesting that other regions of the virulence plasmid are mainly responsible for the growth within mouse liver macrophages in S. typhimurium.