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 sero var Typhimurium genes that are transcriptionally induced when the bacteria colonize the small intestines of mice. These genes were subsequently screen ed for those that are transcriptionally inactive during the systemic stages of disease. This procedure identified gipA, a gene that is specifically in duced in the small intestine of the animal. The gipA gene is tarried on the lambdoid phage Gifsy-1. Consistent with the expression profile, the sole d efect 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 d isease. The gipA open reading frame is homologous to a family of putative i nsertion sequence elements, although our evidence shows that transposition is not required for gipA function in the Peyer's patch. These results sugge st that the bacteria sense and respond to the particular environment of the Peyer's patch, a critical site for the replication of Salmonella serovar T yphimurium.