Tissue-specific gene expression identifies a gene in the lysogenic phage Gifsy-1 that affects Salmonella enterica serovar typhimurium survival in Peyer's patches.

In vivo expression technology was used to identify Salmonella enterica serovar Typhimurium genes that are transcriptionally induced when the bacteria colonize the small intestines of mice. These genes were subsequently screened for those that are transcriptionally inactive during the systemic stages of disease. This procedure identified gipA, a gene that is specifically induced in the small intestine of the animal. The gipA gene is carried on the lambdoid phage Gifsy-1. Consistent with the expression profile, the sole defect conferred by a gipA null mutation is in growth or survival in a Peyer's patch. The gipA strain is wild type in its ability to initially colonize the small intestine and invade the intestinal epithelium. The mutant also survives and propagates at wild-type levels during the systemic stages of disease. The gipA open reading frame is homologous to a family of putative insertion sequence elements, although our evidence shows that transposition is not required for gipA function in the Peyer's patch. These results suggest that the bacteria sense and respond to the particular environment of the Peyer's patch, a critical site for the replication of Salmonella serovar Typhimurium.